Took my K100 to the store about 7 miles away on Friday. Seemed to be running just fine. Leaving the store, I hit second and pinned the throttle. (It's a straight section of rural 2 lane road with little traffic so I wasn't being a dick in traffic, just having some fun.) When the bike made it to about 6500 it just died completely and I coasted to a stop on the shoulder. Tried several starts. No joy. My first thoughts were ignition switch or fuel pump connector but those seemed OK and then I noticed a nice puddle of gas under the bike where the headers mate with the exhaust can.  

When I got it home I swapped in another L-Jet thinking that might be the issue but the bike still made a nice gas puddle in the garage.  Since the injectors were fairly recently refurb'd I doubt it's sticking injectors so I'm guessing fuel pressure regulator. Does the FPR sound like a likely culprit?

The road is a fairly popular MC road so I was able to hitch a ride home to get my trailer pretty easily but the worst part was that I had to ride bitch on a Harley.

I am always a believer that the most recently done job could go wrong and the symptoms do possibly point to injectors......

But what about the vacuum take off beside no 4....goes to the fuel pressure regulator.....

duck wrote:....

The road is a fairly popular MC road so I was able to hitch a ride home to get my trailer pretty easily but the worst part was that I had to ride bitch on a Harley.

Bugger. Did he make you wear a singlet? Those bitches always wear a singlet.

Test the earth connection on the temp sensor. FICU #13 to #10. If its gone open circuit due to corrosion the FICU will be pumping the gas in.

cracked fi hose , before it hits the regulator ?
or a holed injector rail ? or injector seal oring cactus ?

good luck

You also would have disturbed all the fuel lines. If one cracked it could leak down at the point you are describing, especially the one between the rear of the injector rail and the fuel pressure regulator, this would cause a pressure drop at the injector rail.

Holister's check is an easy one and a quite likely one as its very high on the suspect list.

fuel pump relay?

Haven't done anything to it recently other than converting it to paralever which has no impact on the engine.

Fuel lines, filter and vacuum line all more or less new. 

Ordered a brand new FPR (can't hurt) and I'll get back to solving this issue when that shows up in a few days and I install it.

Pull the vacuum line that goes to the FPR, and check for fuel. A couple of bricks have suffered hydraulics locks bending con rods, possibly due to fuel leaking through the vacuum line.
Regards Martin

Busted fuel line is my guess. Around the area of the FPR to be leaking to that area

duck wrote:I had to ride bitch on a Harley.

Hang your head in shame.  

I have a very strict 'no skirt, no ride' policy that I have adhered to for 45 years. Any bloke wants a double, he gotta wear a skirt. No takers to date...

You do realise that 'leak' is a British euphemism for urinating... perfect usage in this case!

Easy to visually check the return fuel pressure. It should be just bubbling out as opposed to a gush which you get at the rail.

One item I found can happen.....damage to the drain pipe from the filler cap drain hole that goes down through the tank....and supposedly into a drip tray sitting on the frame in front of the relay box....

Pipe damaged inside tank? Fuel out the drain hole. Tray missing or no drain pipe fitted....fuel on top of the engine......

I also had an issue where petrol (gas) was dripping onto the exhaust at that same point where the headers join the silencer. When I stopped and put the bike on the side-stand it was pouring onto the exhaust and initially I though it was water and got a surprise when I tasted it. Anyway, it was because the return fuel pipe to the tank from the FPR had a fracture where the pipe had been rubbing on a jubilee clip for one of the rad hoses.
That's one possible explanation for your leak but doesn't explain why the bike cut out.

Dai wrote:You do realise that 'leak' is a British euphemism for urinating... perfect usage in this case!

Same in the US. "I've gotta take a leak." is a very common expression.

When the Harley guy came over to look at my bike I told him it was pretending to be a Harley.

IainM wrote:I also had an issue where petrol (gas) was dripping onto the exhaust at that same point where the headers join the silencer. When I stopped and put the bike on the side-stand it was pouring onto the exhaust and initially I though it was water and got a surprise when I tasted it. Anyway, it was because the return fuel pipe to the tank from the FPR had a fracture where the pipe had been rubbing on a jubilee clip for one of the rad hoses.
That's one possible explanation for your leak but doesn't explain why the bike cut out.

Mine is definitely coming out of the exhaust as the top of it is bone dry.

My new FPR shows up tomorrow.  Figure it doesn't make sense to tearthe  thing apart until that shows up since I'm going to install the new one whether it needs it or not.

If you are 200% positive it is coming out of the exhaust it must be getting into the engine somewhere.

I had this trouble on mine too, I could see fuel staining on the header where it met the block. I got new injectors a few weeks ago and this stopped it. Can only have been a stuck open injector. No other way in and there were no external leaks.

Do you think a fuel injector injects the same amount of fuel as normal when the pressure in the fuel rail is higher than it is supposed to be?  Despite the name, a fuel injector doesn't really inject anything. It is a valve that opens and closes.

The injector is only a valve. The amount of time its open is controlled by the FICU. If pressure behind the injector, in the rail is twice the normal pressure then you'll get twice the amount of fuel delivered.


If its actually leaking from the headers, I can only think of three possible causes.

• The FPR would need to be jammed shut for the rail to be over pressurised and over-fueling. A quick check of the return hose would tell you what's happening with the FPR.
  
• The Tempo sensor earthing may be open due to corrosion. [pin #10 to earth] FICU sees infinite resistance and pumps a sh!t load of fuel.... but this may only happen at startup.
  
• The injector earthing may have a 'closed short' either in the wiring to the FICU [pin #12 to earth] or in the FICU itself. This would mean the injectors are continually open.
  

Holister wrote:If pressure behind the injector, in the rail is twice the normal pressure then you'll get twice the amount of fuel delivered.

It's nit-picking but this is not at all true.  Yes, higher fuel pressure will push more fuel through the injectors but the relationship between pressure and flow rate is not linear.

Fluid dynamics is much more complicated than that and involves fluid properties, flow characteristics, injector design, injector pulse width and several other variables.

(I studied fluid dynamics in depth while getting my engineering degree. It's a very complicated field that involves lots of calculus and many non-intuitive concepts.)

If the diaphragm is ruptured in the FPR fuel will flow down the vacuum line and into number four cylinder or number three on a K75.
Regards Martin.

duck wrote:

Holister wrote:If pressure behind the injector, in the rail is twice the normal pressure then you'll get twice the amount of fuel delivered.

It's nit-picking but this is not at all true.  Yes, higher fuel pressure will push more fuel through the injectors but the relationship between pressure and flow rate is not linear.

Fluid dynamics is much more complicated than that and involves fluid properties, flow characteristics, injector design, injector pulse width and several other variables.

(I studied fluid dynamics in depth while getting my engineering degree. It's a very complicated field that involves lots of calculus and many non-intuitive concepts.)

Correct on both counts duck. It is nit-picking and flow and pressure are not directly related. I actually knew that... just a brain-fart. Fact is you'll get a significant increase in fuel thru the injectors which would be enough to stall the motor. Probably not enough tho to cause fuel to leak from the headers once the motor stopped.

So I did the calculation.
The square root of 'high pressure' over 'normal pressure' multiplied by 'normal flow-rate'.... as far as I understand it. But I'm definitely no expert. I just like to have a go.
So if you have an over pressurised rail at 60psi your flow rate would go from 103cc/min to 145cc/min... roughly

I'm liking MartinW's suggestion above.

Finally got around to fixing this yesterday.

Decided to replace the FPR just for the hell of it.

Moved air box out of the way and replaced FPR.

Checked resistance between L-Jet pins 10 and 13. Nothing. Open circuit.

Went to check temp sensor and the connector fell off! For some unknown reason it was missing the wire clip.  Looked around and the wire clip was nowhere to be found. Must've been abducted by space aliens.

Replaced the clip from a spare harness I had. Then I had about 2K ohms between 10 and 13.

Put top half of air box on.

Fired right up. No longer flooding.

But I'd hit the radiator hose behind the fan and after it warmed up it had a slow drip on that hose. Worn out after 30 years. Ordered replacement silicone hoses.

PROBLEM: Temp sensor connection was loose. (At least it had the decency to come loose when I was only a few miles from home.)

30 Years! why do you always buy junk

I am going to confess my complete and utter ignorance here - how would the missing temperature sensor connector cause the massive fuel discharge?  Is this a causal fallacy? (yep, university for me was philosophy, nothing 'practical').

Glad you got that sorted though.

Infinite ohms from the ECU's temp sensor, meaning cold engine.  ECU would be told to enrichen the mixture, causing longer opening times for the injectors.  But the temperature never rises so the ECU continues to dump fuel. Bingo, flooding.

Mine has done it twice in twenty years, although never to the extent of dripping fuel. I finally cleaned the connection properly and smeared heavy silicone grease around the connector. A temporary on the side of the road fix can be had by removing the fuel pump fuse (No 6 Kraffstoppe)and starting the bike on the existing fuel. As the bike starts to die ram home the fuse, a second person helps. You my need to pull the spark plugs and dry them out.
Regards Martin.

Thanks Robert, your explanation makes perfect sense.  It amazes me how these bikes were engineered.

Woodie wrote:Thanks Robert, your explanation makes perfect sense.  It amazes me how these bikes were engineered.

They're just basic cars on two wheels.