Dear All
help please.  My 1984 k100 has a bad habit of dying on the freeway.  
Here are the contributory factors:
1. ambient temp over 25 degrees C
2. Hot run over 20 minutes including 5 minutes over 5000 revs
3.  Fuel tank down to 5 litres (ish)

Symptoms:
a.  Uneven revs on steady throttle then engine dies as I pull to a halt.
b.  wait for a couple of minutes and will restart on choke!
c.  dies again regularly until allowed to properly cool down.

Other information:
i.  running on 98 unleaded
ii. previously solved problem by upgrading fuel grade to 98 and running some injector cleaner through system but it comes back when conditions above occur.
iii. the bike has done this consistently since I bought it  10 months and 240000kms ago.


Any ideas?
edmate

Hall sensors?

Not picking up the last 5 litres of fuel in the tank due to filter or positioning of pick up?

A frustrating problem but unlikely to be an expensive on I think.

Doesn't quite meet the Hall sensor caper I think. They usually are very definitive about not restarting till cold.
Try a new fuel filter as the injector cleaner will clear some of the crud from the filter and let it run for a bit longer.
Could be the fuel pump I have seen similar symptoms from one when it was dying.  To me it sounds like a fuel problem.

Fuel in the tank getting too hot and vapour lock, lack of insulation under the tank.  If you can feel your fuel rail, how hot is it getting.  Has it only just started doing this or you've only just discovered it?

I had an 85 that did this on a regular basis, but not as low as 25C.  The other factors were the same though, low fuel and hard running

Al

If you decide it's the hall effects, I have a 2nd hand plate here from motorworks that I didn't use.

I have to agree with AL-56 . My 84 K100RT left me standing on the side of the road many a time on a hot day +28c The fuel would start to perculate in the tank and I would have to waite 10 minutes for it to cool down Started the problem once the fuel level was less than half. Fitted a small oil radiator from a Jap bike to the fuel return line to the tank and that was the end of my problem. Do a search of the forum and you will find my article together with a lot of other members ideas.
Lazyboy

I fitted a fuel cooler to my K1100 a short while ago and the temperature of the fuel in the tank is considerably lower.  Mine was so bad that I would get a huge heat rash on my inner thighs, I fitted knee pads which stopped the rash but not the hot tank.

I've had the same problem with my outfit 3 times in the last 5 years. I thought I had cured it when I cleaned and tightened the plug that powers the fuel pump but It happened again only last week on a trip up to Yorkshire.
I'm not sure of the fuel levels each time, but it was fairly low on the last occasion with about 3 litres left.
Each time the ambient temperature was never very high...well it is the UK!

I'll be watching this thread in the hope that someone finds a definitive answer, but, as with all intermittent faults, all I can do is clean various contacts, not knowing if the problem will recur or not.

Paul.

I was doing some work on the RT at the weekend.

I had noticed that the tank was getting extremely hot at the rear by comparison with the LT. When I had the tank off I noticed the air baffles were not correctly in place and in fact were directing hot air up under the tank instead of blocking it. There is a left to right baffle across the intake plenum and air filter that closes off this air passage forcing hot air out the side vents instead of allowing it to travel back under the tank and heat up the rear part. Make sure this is correctly in place.

Secondly there is also a plastic deflector plate under the frame tubes, above the radiator/intake plenum that comes back as far as this air baffle, this stops hot air getting up to the tank and also protects the wiring from excess heat.

Third point is there is a protective insulating sleeve over the fuel rail return pipe........don't be tempted to leave it off.

Edmate wrote:..... the bike has done this consistently since I bought it  10 months and 240000kms ago.

  holy crap! you've done 240,000km in 10 months? That's 6,000k a week.

I think the problems are just your bike indicating it wants a bit of a rest

When was the last time you replaced the fuel filter?

First and foremost I have limited experience in maintaining these bikes. However my ride is 1987 K100RS and my recent acquisition is a 1985 K100RS that is missing a few things including the gas cap assembly. Somewhere on the internet I was told not to buy the original gas cap but to purchase a newer style. I was told that the original 1985 gas cap was prone to causing vapour lock under certain conditions and the later version corrected that by properly venting the tank.
In my research for a replacement gas cap this was the information from a dealer/wrecker "The 1984 & 1985 K100, RS, & RT had a push-button cap that was well known for vapor-locking. I probably have one lying around if you are searching for the OEM cap they left the factory with. I recommend against using the old style, but if you have to have it, call the shop and we can set you up."  I also found on the internet the following " '85 models... * got a revised final drive breather vent * had the spring removed from the fuel tank check valve (due to noise) Mid-1985 models got: * a flange on the end of the engine output shaft, while earlier models had locating circlips. * springloaded fuel cap instead of pushbutton style"
Best of luck to you

Shep

Dear All
The bike died again tonight on the way home, under all the usual circumstances, it being a 30 degree day, the tank almost empty and within 2 k's of my usual stopping point.  At least it is consistent and it was still faster than the train.  The problem first occurred the week I bought it and has occurred several times since but not over the winter months but now things are warming up it's back with a vengeance..
Thank you for your suggestions as a result of what you have said I will be:

1. putting in a new fuel filter ASAP (last one went in 25,000kms ago)
   
2. checking out fuel pump prices 
   
3. checking the fuel rail heat- my engine is getting extra hot at the moment-I was going to flush the radiator and replace the thermostat as well.
   
4. studying the fuel return oil radiator option on the fuel return line
   
5. Checking my air baffle positions and
   
6. getting hold of a new fuel cap
   
7. reading up about Hall sensors
   

I'll be doing 1, 3, 5 first, then 6 followed by 2 and 4, based on the "do the simplest and cheapest first" and see how it goes. 
I am also going to take the "Old Road" on hot evenings.  I am also going to look into buying a stand in bike whilst I sort out the old girl. but I need something cheap cheerful and reliable for less than AU $4k that will not add to my woes.  For example does anyone have an opinion about  the  1994 model K1100RS on BikePoint for $4000? 
 I don't mind living with the occasional stop by the road, it's part of riding an old bike, but I'd prefer to break down as a hobby on a Sunday, rather than professionally during the week
 Thanks again excellent advice every body I'll keep you posted
Edmate

By the way it was only 25000km not 250000 - fat finger syndrome and my rear drive gearbox oil was creamy when I changed it yesterday - after 25,000 k's somethings leaking!