I've previously had overheating fuel problems on my 75s. I had the local trades guild cast a cooler out of aluminium but it only worked at speed not where I needed it in traffic.  I have a laser temperature gun and started recording temperatures at the top of the tank the bottom of the tank and the fuel rail. Fuel rail temperatures were roughly twice the tank temperature. So I concluded the problem was in the fuel rail, one of the engineers came up with a plan to cast a new fuel rail with a built in cooler. I was going to go down that path until I came up with another far simpler plan.

Pre cooler temp.  Ambient     Top of tank    Bottom of tank     Fuel rail

                         27C            39C              44C                     79C

                         28C            40C              45C                     90C

                         29C            44C              47C                     86C

I recorded seven times but these were the highest readings on the fuel rail.

Cooler fitted.       Ambient      Top of tank   Bottom of tank      Fuel rail

                         24C             31C             31C                      26C

                         29C             30C             34C                      26C
         
                         26C             30C              33C                     26C

The above was recorded this morning at different times and has me stumped a bit as the rail is now cooler than the tank and the tank temperature has dropped by 10C. I will continue testing but it looks like the new cooler is working and as the boiling point of fuel is 100C there is a very good margin. The prototype can be improved on
cost me $8.00 Au.

Regards Martin.

The initial boiling point of petrol is 35°C with a final boiling point of 200°C. Water boils at 100°C but because petrol is made of many different chemicals each has its own boiling point.  Usually you will see petrol actually boiling and bubbling at around 45°C.

waiting for the picture martin
by the sound of it you have placed it in the high pressure line before the injector rail ?

good results none the less

At the moment I'm just running the prototype. The whole set up is really simple piece of aluminium sheet with holes drilled to match the fuel rail and the mounting holes. I glued double sided reflective fire resistant foam onto the back of the aluminium. I then removed the fuel rail and injectors, and separated them. I placed the aluminium heat shield on the rail and clipped the injectors back on. A small amount of insulation has to be removed to allow the clips to be fitted. The whole assembly is then pushed back on with the aid of a bit of silicone grease around the "O" rings. A small bend has to be placed in the heat shield just above the injectors. No mounting screws are needed and everything is quite firm. The MK 2 version will have smaller mounting holes in the aluminium be shaped a bit more on the trailing edge and possibly be painted black. I'm still scratching my head on how effective it has been. The temperatures aren't high enough to test it fully that will have to wait, however I did give it a bit of stick and it still didn't make any difference. I looked up the boiling point online and I came up with 95C to 100C on four sites.
Regards Martin.

Hi Martin, following this thread with interest. Curious to know what the fuel temperature problems were with your K75 as I have one too. Was it the normal "hot tank burning the insides of the thighs" syndrome. 

I have been lucky in that in my normal riding position I sit with my legs slightly away from the tank and only grip the tank with my legs when I am in fairly serious go hard mode. Don't know why I sit like that - just happens, so don't feel the hot tank as much as some of my friends.

Cheers

So... here's an obvious suggestion  . Make one in the shape and size of the fuel injector cover that Motorworks sell?

[Edit]. Idiot. That wouldn't work because it would be mounted on the anti-vibration rubbers.

Dai once I had done it, it seemed so obvious. And I wondered why it had not been done before? I got the idea from my hot Holden phase where we used to make aluminium heat shields to go under the multiple carbies to stop vaporisation. Gaz my tank did get hot, but the main problem was vaporization from riding in stop go traffic in Queensland summer days 30C+. The way it is now working is that the fuel rail is now cooling the tank. Comparing the two 29C days there is a drop of 13C + in tank temperature. The rail temperature has a massive 40C drop. There are a couple of problems still to be solved. You can't clean around the injectors before you remove them, with the possibility of debris entering the injector holes. I've come up with two possible solutions a small hose and try and vacuum as much as you can before you remove it and vacuum the injector hole after removing. Or some large heat resistant foam rings around the injectors to stop the dirt getting around the injectors.
Regards Martin.

I love it when people solve problems that might or might not exist. I would never try to cool fuel down that was too hot till I know what was deemed as too hot. BMW must have been aware of fuel temperatures when they designed, tested and built the K, but to my knowledge has never published the figures, so how do you know that it is too hot?
My RS tank used to get hot on the inside of my knees when riding in shorts in the summer, 35c+, but the inside of my legs are not an ISO standard measurement of heat. 
Fuel under pressure after the fuel pump has a much higher boiling point than fuel in the tank.

Bob I used a laser temperature gun to determine the temperature of the tank and the fuel rail. I determined that the fuel was getting too hot when it would stall and die in traffic on 30C+ days to the point where it was dangerous and I nearly got rear ended, multiple times. The temporary cure was to run with a full tank of fuel which stopped the fuel from overheating or avoid traffic on 30C+ days. 30C + days on the main roads were never a problem.
Regards Martin.

too hot is when you have to wear high insulation pants to prevent scorching your skin bob

the ambient temps around this area during summer , including the high humidity  do not make for a very cooling effect to anyone on a k bike , especially when the fan kicks in blasting 90 + c temps though out the system past the end of the fairing lowers

there is no lower fairinged k bike that has "some" cooling offered to the fuel system ...its all passive insulation reactions,  worth little out here at all especially after the "cooling air" passes through the radiator .

30 +_ means nothing  ...was  a pleasant 32 c out here just yesterday but the cooling effect of low humidity , different to our summer of 90 +% meant that it was delightful riding weather for us . rather than the radiant heat off the road at over 40 + c (closer to 50 +c ) from November till April 10:00 hours till 18:30 hours just as an indicator .

Dai mentioned the injector cover mounting solution ...would be great idea  if the cooler was outside of this ...the cover would offer some insulation properties from the behind radiator heat effect …  just the amount of cooling btu units available outside the cover could make this work well ...


possibly a tube outside of the radiator directing air to the fuel rail could be a thought ??

What I am asking is what temperature is being used as a datum? BMW will probably not give you that temperature so taking readings means nothing.
Heat from the engine is directly proportional to the amount of fuel being burned, and that heat should be directed away from the rider if possible. The more fuel you burn then the more heat will be generated. As said BMW did some testing with the K when they designed and built it and would have run in very hot and very cold climates. I am sure that fuel temperatures were not a concern. If you want to get rid of more heat then fit a bigger radiator, and treat the cause rather than the result.
You want heat, then try riding a Ducati 939 Supersport on a day when it is 40c, the inside of your legs will fry from the exhaust on the rear cylinder. My K is cool in comparison.

Bob I'm not worried about the engine cooling system, it copes fine in traffic. I'm not worried about a hot fuel tank. What's not fine is getting rear ended in traffic, because the bike cuts out as you take off. I'm not alone with this problem there are quite a few people running various types of coolers.
Regards Martin.

BobT wrote: If you want to get rid of more heat then fit a bigger radiator, and treat the cause rather than the result.

 fitting a bigger radiator will not get rid of more heat ...it will just retain the heat whilst the thermostat passes fluid above a certain temperature then it closes ..is the design that bmw employs on the k bikes
there is a bypass pipe utilizing the feature of passing cooler fluid till the engine fluid reaches thermostat temperatures ...then as it approaches running temps it closes ...passing more hot fluid through the radiator as it reaches the thermostat temp
ye gods 
what were you thinking ?

typical


the cause is that the fairinged bikes were designed to retain heat ...the bubble created behind the fairing does just that ...there is nill designed airflow through the fairing proper to cool the rider ..in fact they designed and fitted fork diaphrams below the yolk to stop air passing.. all for autobahn riding experience   and nothing to do with city commuting  .you do over think the design and market they were trying to attract ,,its a typical bmw ploy to gain sales no mater what the cost .

latter mods included cups to attempt to direct air into the fairing headstock , behind the forks ..but this Is all a failed design flaw  yes good at highway speeds but in traffic with little airflow zilch effect .they even reduced at the same time the heating effect of the radiator by reducing the cores in the radiator from 3 to 2 … in fact anything below 80 kph (in traffic ) around here does little for cooling 

so I took my fairing lowers off .added a fuel cooler in front of the radiator  , reinstalled a 3 core radiator , made a duct to direct air up into the lower tank and fairing area and dropped the riding temperatures by at least 10 - 20 c degrees at the tank ...actually the tank is at atmos temps and the bubble of air behind the screen is 3 degrees above atmos ...very different to the high 50 degree + tank temps and burnt inner thighs that I experienced  before modifying … 

 if you want to find the solution you gotta think better than just a bigger radiator
yeah it looks like a dog ...but works for me ...perhaps one day the lower fairings will go back on ...with a bit more experimenting


 ……. ATGATT

charlie99 wrote:

BobT wrote: If you want to get rid of more heat then fit a bigger radiator, and treat the cause rather than the result.

 fitting a bigger radiator will not get rid of more heat ...it will just retain the heat whilst the thermostat passes fluid above a certain temperature then it closes ..is the design that bmw employs on the k bikes
there is a bypass pipe utilizing the feature of passing cooler fluid till the engine fluid reaches thermostat temperatures ...then as it approaches running temps it closes ...passing more hot fluid through the radiator as it reaches the thermostat temp
ye gods 
what were you thinking ?

typical


the cause is that the fairinged bikes were designed to retain heat ...the bubble created behind the fairing does just that ...there is nill designed airflow through the fairing proper to cool the rider ..in fact they designed and fitted fork diaphrams below the yolk to stop air passing.. all for autobahn riding experience   and nothing to do with city commuting  .you do over think the design and market they were trying to attract ,,its a typical bmw ploy to gain sales no mater what the cost .

latter mods included cups to attempt to direct air into the fairing headstock , behind the forks ..but this Is all a failed design flaw  yes good at highway speeds but in traffic with little airflow zilch effect .they even reduced at the same time the heating effect of the radiator by reducing the cores in the radiator from 3 to 2 … in fact anything below 80 kph (in traffic ) around here does little for cooling 

so I took my fairing lowers off .added a fuel cooler in front of the radiator  , reinstalled a 3 core radiator , made a duct to direct air up into the lower tank and fairing area and dropped the riding temperatures by at least 10 - 20 c degrees at the tank ...actually the tank is at atmos temps and the bubble of air behind the screen is 3 degrees above atmos ...very different to the high 50 degree + tank temps and burnt inner thighs that I experienced  before modifying … 

 if you want to find the solution you gotta think better than just a bigger radiator
yeah it looks like a dog ...but works for me ...perhaps one day the lower fairings will go back on ...with a bit more experimenting


 ……. ATGATT

+10 Exactly thanks for saving me the time of typing it Charlie

Thanks Charlie and Rick. Although the heat shield has worked and has gotten down the fuel rail temperature to ambient temperature, I am also working on a back up. In traffic at 40C I'm assuming (hoping) that the drop has been enough to stop the vaporization. I'm off to the Trade Guild this morning and I'm going to see if I can cast a bar of copper. I'll then mill it down to fit tightly over the fuel rail, and mill cooling fins into it. If the shield does not work enough this summer. I'll then either attach it by silver soldering or clamp it on after coating it with heat sink paste. I'd appreciate fuel rail and tank temperature readings from inmates with coolers fitted, with this information I can do a comparison.
Regards Martin.

Can you clarify this approach?  If the radiator is passing heated air back over the fuel rail and/or other segments of the system, wouldn't any heat sink or whatever it's called just pick up that air's heat and conduct it to the fuel passing through the pipe?  
It seems to me that a solution to the problem must somehow pick up cooler air from in front of or otherwise apart from what passes through the radiator.

BR I found that when I took temperatures with a laser temperature gun the fuel rail temperatures were approximately twice the tank temperature. And I thought the simplest way to get rid of the heat was to isolate the rail from the engines heat. The aluminium shield has double sided reflective foam glued on the back. Heat from the engine is now blocked from the rail by the shield. Back in the dark ages when playing with souped up cars with multiple carbs they could suffer vaporization. The fix was to make an aluminium heat shield to go between the carb and the manifold.
Regards Martin.

martin has a k75 s model ...so its a bit complicated
but does have the advantage that the fairing doesn't wholly cover the engine area  and some of the injector path is open to the air , albeit it is behind the radiator  to a fair degree

will be interesting to see the results and what he comes up with

ill try and do some running measurements martin , the remote sensor on the temp gauge has about 1 metre of lead length so I can strap it almost any where ...but the range of measurement is unknown at this moment on this gauge  ,  the range of what is happening on the fuel rail should be ok ...just have to isolate the intermittent air going past from the wash off the radiator affecting the sensor at different speeds etc  ...blue tac to the fuel rail  perhaps ?

I do have an ir gun at the office , but at the moment the borrow options have changed with the management  crew in place .

Charlie I'm about to head of to the Trades Guild and there are a couple of hopefully cluey engineers. I'm going to get their opinions on what's going on.
Regards Martin.

forgotten if you have a belly pan on martin , I seem to recall that you do ?

had though that a tube from between the bottom of the radiator and engine could be fitted to direct cooling air past the throttle body lowers at the injector rail ? at least ventilate it ?? effect would only be whilst moving forward though .

My tank used to get hot enough to literally burn me. I bought a generic oil cooler radiator on eBay, ran the fuel return line through it so it’s not under pressure in case of a stone hit and mounted in front of the radiator. 
No more burnt thighs and a lot more comfort even in summer. 

Bill

Something about Martin's temperature readings on the rail doesn't sound right to me.  Not seeing how he took the readings I suspect that his IR gun is picking up background heat from the cylinder head.  It might be worthwhile to retake the rail temperature readings with a shield to block the heat from the cylinder head.  If that was done, I would wager that the rail temperatures would not be quite so high.

I had problems with boiling fuel in the tank on my K75RT along with slow roasting my thighs on hot days.  My solution was to locate a fuel cooler in front of the engine  and tap into the return line from the fuel pressure regulator to the tank.  Without taking readings I can say that this cooler allowed me to ride in relative comfort without boiling the fuel in temperatures well above 40C. 

Unfortunately, my solution only works with K75 models that don't have engine spoilers(belly pans).  The extruded cooler is too large to work in the space behind the front wheel on K100 models and in front of an engine spoiler on any K bike.

The cooler I have and the one Charlie has are meant for a power steering cooler and is 6in x 4in and mounts on the left upper side of the protection screen in front of the radiator. Not sure but I think I identified it as a Davies Craig brand.

I've no intention of high jacking this thread, but will say I've taken an interest in this challenge.  I didn't quite understand what all the fuss was about when I owned the K100RS.  The 1996 K1100LT runs a whole lot hotter!  
I think I still have a three row radiator in the shed.  Do you think that would make any worthwhile difference?  I ask because is seems to me that the easier solution might be a thermostat that opens sooner.

Just got back from the Trades Guild. Had a talk to a couple of engineers one a ships engineer and a heat engineer. I showed him what I had done and how and where I was testing and he said it was fine. I then asked for an explanation of the dramatic difference between before and after. He went into a technical explanation about insulation from heat sources versus cooling after it had heated up. However he also stated that as the daily temperature rises I might have to add cooling to the fuel rail. I told him I had already thought of casting  a finned copper heatsink. He came up with another more efficient method using copper sheet. He did say that I should wait until summer and take more readings and that I should paint the shield black. This morning took some more readings ambient temp 14C Top tank 18C Bottom tank 23C Fuel rail 18C. After being left out in the sun getting stuck in traffic and giving it a bit of stick on the short 15 min ride home Ambient 27C Top 35C Bottom 38C Fuel rail 33C Cyl Head 66C. All temperature readings taken in the same places the fuel rail temperature reading was taken in the centre of the rail. Gryph the rail temperature is now low, and Charlie you are correct I do have a belly pan. I don't have the small plastic bits that go on the lower edge of the fairing fitted.
Regards Martin.

brickrider2 wrote:I've no intention of high jacking this thread, but will say I've taken an interest in this challenge.  I didn't quite understand what all the fuss was about when I owned the K100RS.  The 1996 K1100LT runs a whole lot hotter!  
I think I still have a three row radiator in the shed.  Do you think that would make any worthwhile difference?  I ask because is seems to me that the easier solution might be a thermostat that opens sooner.

Its the heat coming from the radiator that is a lot of the problem

just an up date ..on the way home from the office   left work with ambient at about 35c ….soon after whilst travelling cooled to about 28 c ...an hour in the usual stop go  traffic idling at lights  continuously  almost all the way home ….funnily enough heading south in the afternoons is travelling with the wind .. its the way it works around brissy with the late afternoon prevailing winds onshore up the river

fuel rail was highish temp at 38 c  (likely heat transfer from the head  so close and compression heating effect of the fuel rail under pressure and so long times idling rather that moving  ) ...temperature readings from the return flow to the water pump in the 90s …..but tank temps about 4 degrees above ambient   which for this old goat means its doing its job ...about 3 - 4 litres left in the tank ...so not a lot of cooling going on with the fuel flow back to the tank as the transfer has no time to settle ...not to mention the likely heating cycle of the radiator heat transfer to the tank ...and legs

tappet cover after stopping for about 3 mins was in the mid - high 40s ...head temp was in the high 60s  closer to 70 c .. tank temp  a mere 28 c …..ambient  about 24 c ….in other words ..quite comfortable  (hate to mention that just a few years ago tank would have been in the high 40s under the same situation )

ill give it another run ...with a near full tank which should even out the temperatures in the tank with a larger mass of cooled fuel moving through the system ...imagine this on a highway with good airflow all the time ...its got to be worth it  for us lot ...as rick g  and others have mentioned  already

there maybe other ways of achieving the same result ...lets see

Thanks Charlie, if I'm in the mood I might try and paint it tomorrow. I was going to modify it slightly with the MK2 version. But the general consensus at the guild was to leave it but paint it black.
Regards Martin.

Martin, when you paint, try for the thinnest film that gives a solid coat.

Thanks Gryph will do. Too much time on my hands, so I did a bit of thinking which can be dangerous. What the guy at the Guild said makes sense, is it better to try and cool something down after it has heated up or try prevent it from heating up in the first place. The source of heat in the engine comes from the combustion of fuel in the cylinder head. Besides the injectors which are partially insulated from the rail ( no metal to metal contact) the main entry of heat into the fuel has to be via the fuel rail. If you insulate the FPR and the lines and shield or insulate the rail you should eliminate most of the sources of heat entering your fuel system. I will have another conversation with him now that I have mulled it over. Besides the reading I took on my own rail it would be good to see other rail temperature reading from Bricks not fitted with fuel coolers and their ambient temperatures at the time. And I could be mistaken but weren't some Bricks at some stage fitted with insulation over the fuel rail. Not sure whether this was OEM or aftermarket.

Regards Martin.

MartinW wrote:...The source of heat in the engine comes from the combustion  of fuel in the cylinder head. Besides the  injectors which are partially insulated from the rail ( no metal to metal contact) the main entry of heat into the fuel has to be via the fuel rail. If you insulate the FPR and the lines and shield or insulate the rail you should eliminate most of the sources of heat entering your fuel system...And I could be mistaken but weren't some Bricks at some stage fitted with insulation over the fuel rail. Not sure whether this was OEM or aftermarket.

Regards Martin.

Martin,

Interesting post... 

On my K100LTs (2 + donor), all the fuel rails are insulated, so I suspect that this is an OEM fit as standard. These are all European models, so not designed for running in especially hot climates. The insulation is easier to see in the pics of the fuel rail off my donor bike (yes, it is awaiting the paint treatment). 

The insulation effectively wraps 3 sides of the rail and just clips around the bottom side (about 3-4 mm thick).

Pic 1: Underside (uninsulated)


Pic 2: Fuel rail top side (held in as-fitted orientation with those come in handy ear plugs)


Pic 3: Outboard side (furthest from engine)



Pic 4: Underside of rail (held in vertical orientation)


...and a few blurry pics 
Pic 5: As fitted. Aft end of fuel rail not insulated and external to fairing lower assembly)


Pic 6: Centre section of fuel rail as viewed between lower left rear fairing vent



Pic 7: Fwd end of fuel rail as viewed through front left fairing vent


It makes sense that the heat in the fuel is being picked up as it is circulated through the fuel rail. The fuel pump and Fuel Pressure Regulator should ensure that the fuel rail is always full of fuel under pressure, which either is squirted into the cylinders when the fuel injectors open and burns (creating power and waste heat from combustion) or is sent back to the fuel tank via the return line.  Once the engine block is up to normal temperature, with little natural air cooling (particularly on fully faired bike) in the vicinity of the fuel rail, it is not surprising that the fuel rail also heats up - mostly though convection (being surrounded by hot air) rather than by conduction (metal to metal contact) as the two mounting bolts are insulated from the fuel rail (as shown in blurry pic 4 above) and, therefore, the fuel within the fuel rail will also heat up. The now heated surplus fuel returns to the fuel tank where it will mix with the, initially cooler, bulk volume. After a period riding, the temperature of the fuel in the tank will start to increase due to the constant flow of hot fuel back to the tank - and the longer you ride, the volume of fuel in the tank will steadily reduce, which means the remaining fuel is going thorough the pump-rail-return cycle more frequently and therefore getting steadily hotter. Of course it can never get hotter that the engine block temperature, but that is unpleasantly hot and this will be noticed by the rider as the fuel tank starts getting above 45 deg C.

Here in the UK (as evidenced by Audi Bobs post on burnt London legs), we have had an unusually hot spell of weather this summer - typically 27-32 deg C and, even with insulated fuel rails, I have noticed the fuel tank heat through my normal riding gear (with winter thermal layer removed) and the tank is physically very warm to the touch and it certainly gets more noticeable when down to less than half a tank of fuel. I appreciate that these temperatures are nothing compared with those experienced down under - for most of the year, but the fuel heating effect is still noticeable. In the winter, of course, it is a bonus!

So what has your add on device achieved? I suspect that it is acting more as a heat shield/baffle than a cooling fin - i.e it is simply channeling the wild heat from the engine block away from the fuel rail so the fuel rail doesn't get quite so hot, rather than taking the heat from the fuel rail. If that is the case - painting it matt black would actually make it less effective as it would probably absorb more heat from the engine (unless you had it shiny on the inside to reflect the engine heat and matt black on the outside to absorb any convected heat from the fuel rail - although, in hot climes, matt black could add an unwanted solar heating effect to the fuel rail, especially if the lower fairing has been removed). 

So what's the solution? The add on return line fuel cooler is a good option (as per Rick & Charlies set ups) for physically reducing the fuel temperature before it goes back to the tank. Screening/insulating the fuel rail is a must-do to try and reduce the convected heat heating up the fuel rail. Also worth checking that the insulating arrangements for the fuel rail mounting points are in good shape - if a previous owner has removed them and allowed a metal to metal contact, you will definitely have a much worse problem!

I guess this is always going to be a problem with fuel injection - constantly churning fuel around a system until it eventually gets burnt. You wouldn't have this problem with carbs (but plenty of other problems instead). Net result is the whole fuel system steadily heats up as you ride.

The bit that still puzzles me though, is your symptoms of the bike dying (and nearly getting rear ended) when riding in hot conditions. You put this down to the fuel vaporising (in the fuel rail?) and therefore starving the engine of fuel. ("but the main problem was vaporization from riding in stop go traffic in Queensland summer days 30C+"). The fuel pump and FPR are designed to keep the fuel rail constantly full off liquid fuel - hence you should not be getting vaporisation within the fuel rail. As Bob T mentioned, the boiling point of liquids increases with increasing pressure (this is how we operate pressurised water nuclear reactors - substantially increasing the water pressure increases the temperature at which the water boils and therefore we can keep it in the liquid phase at temperatures well in excess of the normal boiling point of water which is better for removing the thermal energy from the fuel and provides more energy to heat a secondary water supply to create steam for power turbines). So, if you are getting vaporisation in your fuel rail, that suggests to me that you have some other problem over and above just the fuel heating issue. 

As suggested in previous posts, the boiling point of petrol is typically about 95 deg C at ambient pressure (1bar) but individual components that make up your particular blend of petrol will boil at lower and higher temperatures. I recall that the FPR controls the fuel rail pressure at just over 2 bar (36 psi), so this will probably increase the petrol boiling point to something like 115 deg C. Therefore, unless you are getting really hot...it is unlikely that the petrol will be vaporising in the fuel rail. Are you running at a reduced pressure (FPR problem?) - that would certainly exacerbate your problems and give poor running. The other option is have you started using a different grade/brand of fuel? If your particular grade has a higher level of components with lower boiling points, then you could experience vaporisation of these components at much lower temperatures which could cause vapour locking of fuel lines or the fuel pump impeller - both of which will effectively interrupt your fuel supply temporarily. Another thought, have you fitted an after market fuel pump that has a higher volumetric flow rate - i.e. churns the fuel around the system quicker than the OEM pump (net result, even more heated fuel going back to the fuel tank by the return line than normal - offset to a degree by less stay time in the hot zone of the fuel rail)

Sorry - rambled on long enough and I've probably confused more than helped!

yes agree with bae

insulation of the rail is stock , additional insulation of the fuel lines does help indeed
until just recently all my fuel lines were additionally covered with air conditioning type insulation (about 16 mm thick )

the return fuel lines still have it fitted from regulator back to the tank (via fuel cooler )

and , for looks I have stripped the injector rail of its insulation ( I imagine that that contributes to the heating of the injector rail )

but will apply insulation again on the pressure feed from tank (just behind the radiator ) to the fuel rail  and remeasure the effects

its been 8 years (or more ) since that piece of hose has been installed and is now showing some cracks in the outer  
 and the reason for stripping the insulation off  it just lately .

as said I believe it will make some difference

interesting to note with the cooler in front of the radiator on applying  the fan to cool the radiator whilst sitting in traffic I do see a lowering of the fuel rail temp by a couple of degrees and after a couple of minutes operation , likely due to the low fuel load in the tank

I imagine that the pressurized fuel from tank to regulator moves fairly slowly so is exposed to additional heating for quite some period  a minute or more ? depending on pump flow characteristics at pressure ?

the insulating of the fuel lines has been discussed a few times previously . with good results noted by many in the hotter climates ...lower us states etc as well as my self ...maybe some 6 years or more ago

so I suggest to martin if he hasn't already done so, to look at this as a contributing factor (its cheep to do and does work to a degree at keeping the tank, fuel cooler  )

I don't believe my 75s has ever had rail insulation, and I can't remember ever seeing it on any OZ bricks. All my mates bike are free from rail insulation 2 x 75 RT's 1x 75s and 1 x 100 RS 16v. If it was fitted it was probably removed by previous owners. I have insulation on my return line, but none on the FPR which I will look at doing. The rail mounting insulators are in place. The FPR has not been modified and is running at 36PSI. The shield that I fitted has double sided reflective outer with a fire resistant foam core fitted on the engine side. The underside of the tank has also been fitted with the same reflective foam. Picture number two shows the reflective foam.

The cutting out symptoms on a hot day in traffic could be eliminated by running a full tank, I estimate that the problem would occur when I had about 7-8 litres left in the tank. this was occurring before the low fuel light activated. This has only occurred the last three times that I tried to go into Brisbane  on 35c + days. I have previously never really driven in traffic in that kind of temperatures. This was occurring before the low fuel warning light activated.  The bike would cough, splutter and sometimes cutout  mainly on take off sometimes you could keep it alive by manipulating the throttle. The last time this happened I pulled into a service station and filled it up, the traffic was even worse but the problem did not reoccur.

The couple of things I didn't do was check any temperatures as I didn't have my temp gun.  I also didn't check the tank for boiling fuel which has been documented by other brick owners. I did have a problem latter with a collapsing return line but the symptoms were totally different. I will now have to wait for hotter days to see if it still occur with the shield in place the temperature gun has now earned a permanent spot. The temperatures taken on a 28C day minus the shield showed a rail temperature of 90C a 29C day with the shield show a rail temperature of 26C which must have a slight error as it is under ambient. But even with that error it is a third of the pre shield temperature.
Regards Martin.

Mine has the insulation on the fuel rail but it only covers 3/4 of the rail, almost like it was designed for a K75

just a word of advice marc ,  take the insulation off and check the rail for corrosion , and pits in the metal

have seen a couple near eaten through    after cleaning and stabilizing-filling   the insulation can go back on




ooops ...better pic


good luck

I certainly don’t discount the effect of heat coming into the system via fuel lines and fuel rail.
However, when I was experiencing burned legs from my tank, my forum research pulled up a lot of references to heat going into the tank from it’s underside, and the importance of the factory insulation there being in place and even added to. 
Given that a lot of heat given out by the radiator goes to the space under the tank, this makes sense, even allowing for the various plastic parts restricting direct air flow to the bottom of the tank.

Again, not doubting the truth of the vapour lock and engine faltering issue I’m at a loss to understand it, as the entire feed side of the fuel system is under pressure which raises the boiling point.
Even at it’s leg-burning worst, my red RT never had the issue even at 43C temps in outer metro traffic and all fairings in place. 

Bill

That's a very good point you raise Bill, about the fuel being under pressure. The only times I have had problems were on extreme heat days, the most memorable being a few years ago on the Northern Tablelands ride when I thought I had pump problems and replaced the pump after which it ran well but in the time it took to change the pump the fuel cooled down. The fuel was so hot I had to wait about an hour for it to cool before I could get my hand into the tank to get the pump out.
I still don't really know if it was that the fuel was hot enough to create a vapor lock or that the pump was failing and I replaced it when it was not needed.  This was when I had a small cooler in the fuel return line.
Getting back to the fuel being under pressure so making it that it should not vaporize as easily I have yet to see any explanation that does tick all the boxes.

Bill there are a couple of things that point to a heat issue. The problem only occurs on 35C + days in traffic and with approximately a third of a tank left. When the problem occurs pulling into a servo and filling it up alleviates the problem. Never happens when not stuck in traffic even at low speeds 50 Kph. I've yet to experience a really hot day with the heat shield in place. The closest I came was the other day 34C in moderate to slow traffic about a third of a tank left and the fan cut in on auto. No sign of fuel problem ambient temperature was 34C top of tank 41C bottom of tank 47C and fuel rail below ambient temperature 29C.

There are a couple of engineers at the local trades guild, one who is a heat engineer and I'm going to ask about why the rail temp is running lower than ambient. He has previously checked on how and where I'm checking temperatures and said the way I am doing it is fine. The bottom of the tank is insulated with fire resistant double sided reflective foam the FPR is insulated with reflective tape the line from the rail to the FPR is insulated with foam insulation as is the supply line. The return line from the FPR has thinner insulation and will be upgraded to the thicker foam. I am currently waiting for a 35C + day to go further testing in traffic. Also the next time I go for a group ride I'll take the temp gun and take reading from other bikes. On one of the other brick sites there were pictures posted of fuel boiling in a tank.

Regards Martin.

According to the Haynes manual, in extremely hot weather the RS and RT/LT versions suffer from fuel evaporation in the fuel rail. I think I have suffered from this as I used to loose power after long periods on full throttle then using it in stop go traffic. If I stopped for a while the engine would run properly for a while then the symptoms would return. I now have a problem when my fuel level drops to 6 litres. I think I have crap in the bottom of the tank, I need to get the bike to the garage with low fuel, then I can remove the tank and clean it.

Thanks Stumpy. The part is under Fuel System And Lubrication 6.9 in part 13 titled Tank Insulation.
Regards Martin.

yeah we covered quite a bit on that under tank insulation … a long time ago now

but its imperative for any riding in moderately warm to hot climates to get that insulation fixed up ...in many cases there was chaffing etc that had lifted the insulation barrier or affected the coverage of the under tank ..enough to make a difference at least

a few good solutions were found along the way

maybe worth searching the forum for those finds

from memory just one contribution was by old goat ...restoring  his "bismark" fabulously with great work and quality thought in the build \\there were two parts    starts here  https://www.k100-forum.com/t1941-85-rs-restoration-part-1 

but the posts are in here some where ...just need to get creative and search for the right qualifier for under tank insulation  I guess

good luck

MartinW wrote:At the moment I'm just running the prototype. The whole set up is really simple piece of aluminium sheet with holes drilled to match the fuel rail and the mounting holes. I glued double sided reflective fire resistant foam onto the back of the aluminium. I then removed the fuel rail and injectors, and separated them. I placed the aluminium heat shield on the rail and clipped the injectors back on. A small amount of insulation has to be removed to allow the clips to be fitted. The whole assembly is then pushed back on with the aid of a bit of silicone grease around the "O" rings. A small bend has to be placed in the heat shield just above the injectors. No mounting screws are needed and everything is quite firm. The MK 2 version will have smaller mounting holes in the aluminium be shaped a bit more on the trailing edge and possibly be painted black. I'm still scratching my head on how effective it has been. The temperatures aren't high enough to test it fully that will have to wait, however I did give it a bit of stick and it still didn't make any difference. I looked up the boiling point online and I came up with 95C to 100C on four sites.
Regards Martin.

So now, one year later, what does the current version of this heat shield look like, and what are its improvements? Inquiring minds want to know...

It's still the same, I was going to paint it black but it might have interfered with heat dispersal. As far as a mark 2 version I don't know what to improve.  It's actually working well and there has been no reoccurrence of the overheating of last summer on really hot days in traffic. On comparisons with other Bricks K100's it is running 30-40 C cooler. The hottest I've seen on the fuel rail was 55 C which is well under the boiling point. When summer hits again I'll keep doing temperature comparisons. I hope that the Cane Toad will give me a chance to find a K75s to compare temperatures with. Not many 75's around these days.
Regards Martin.

Martin, have you considered polishing or painting the fuel rail silver or white?  That could make it less heat conductive and maybe lower the fuel rail temp a few more degrees.

Duck if this hadn't worked as well as it did, it was on the list of further mods. A few other ideas were to add copper cooling fins to the rail. Another idea was to cast up a new rail with built in cooling fins. But it seems to be working well so far as it is. I'm looking forward to comparing it to another 75. The only bikes that I have done a direct comparison with is Matts K100 and I think it was a difference of 40 C for the same ride. 
Regards Martin.

Easy way is when you pull up at the servo 

Grab a bag of ice throw 1/2 into your pannier to keep the tinnes cold and tip the other half of the bag into the tank 

This will keep you fule nice a cold like an esky

A good place to look for material to insulate gas lines, fuel rails etc is at a auto store that supplies stuff to the racing or hot rod crowd.  They have several different ways you can insulate lines etc. Some of it even has velcro closures so it is easy to work with. I looked at some today that had velcro closure and you could just cut out the portions to clear the injectors and wrap the rest of the fuel rail. They are made of reflective material and designed for the purpose of insulating hoses.

This winter I plan on adding a cooler to the return fuel line and will put some of the insulation material on the fuel rail.  Not good with pictures but when I get it done I'll try and upload some.

All my external fuel lines have been covered in 13mm ID 13mm thick foam insulation since May. Bought it from Bunnings for around $4.50 Au a metre.  It was a tight fit and required coating in talcum powder to get it over the hose. When we did the Kane Toad Rally some pretty high temperatures were encountered and after one stop my dash thermometer was showing 49 C which dropped to 41 C when on the move. Since doing all the mods and encountering some pretty high daytime in traffic temperatures my brick has shown no signs of vaporization. However I am thinking of maybe remounting my fuel cooler or another one as it did work at speed and therefore may be of some additional benefit.
Regards Martin.

I insulated the return line with Armaflex foam tube.
It's somewhat awkward to install but in the end this worked very well.

Last summer three of us did the Paul Bellthorpe memorial motocross ride on a really hot day. The Bricks got a real workout on what is a vey hilly rough four wheel drive track. Both Paul and Mick complained of excessive tank temperature while mine was still comfortable. After running the heat shield for 2 years with no more overheating problems, I decided to build a Mk 2 version to fix a inherent problem with the Mk1 version. 

While the Mk1 version cured the overheating problems, it added a couple of problems. In order to balance the throttle bodies/idle adjust the fuel rail with injectors has to removed and the heat shield removed. You then have to refit the rail/injectors and balance the throttle bodies, and then remove the rail and refit the heat shield. 

At the moment I'm in the process of doing a modified heat shield that is in two pieces the bottom part slides under the rail and the top half screws onto the tabs on the bottom half via Nutserts. While the bottom part of the shield will still be fixed the top half will be removable allowing access for maintenance. If it works I'll post some pictures, it's in a design as you build stage at the moment.
Regards Martin