I have a 1985 K100.I bought it in November as a non runner.I finally managed to get it to fire up today after replacing the fuel pump and relay.My problem is that it runs rough and stops after a few seconds.If I try to open the throttle it stops.The rpm is very low(less than 200),as if it was only running on a couple of cylinders,which is probably why it's stopping.However all the exhausts are hot,all the plugs are firing(and in the correct order) and all the injectors are working,but it won't run as it should.All the filters have been renewed.Any ideas please? Best wishes.John

Did you it a new fuel filter in the right direction? This could be a few things, like dirty injectors, a not working fuel pressure regulator, badly seated ECU plug, etc. What was wrong with the fuel pump/relay?
Normally the bike starts and runs up to above 750 rpm after which the ECU takes over, so continuous running at 200 rpm is strange.
Is the airbox properly connected? I mean the elbow between the filterbox and the plenum.
These bikes are very sensitive to electric issues, nothing difficult, but one of the first things you need to do is properly clean all the electrical connections, only then can you really start fault-finding.

hi john.... welcome to the forum

possibly a couple of things ....things we have seen recently of a similar mature


first check the tank fuel pump connector located under the right hand side cover ....known to be intermittent


fuel filter and rubbers inside the tank ....

fuel presure regulator (behind the throttle bodies ) could be stuck shut ...or open ...highly likely as it sounds like you are starving fuel presure


temperature sensor on the fluid stub (behind the radiator )

air temp sensor ( its a small thermistor on the inlet of the afm (inside the top cover of the air box )) could be dirty ?

high tension leads / coils there are 2 one for 1 and 4 one for 2 and 3 measure the leads in pairs you should get about 18000 ohms from one end to the other its not unusuall that they have a open circuit some where in the coil pack or leads ...

hall effect sensors behind the timing cover at the front of the engine they have been noted to go faulty and heat apears to be the indicator of failure... but unlikely

air breather between the plenum and the engine crankcase (only about 18mm thick tube but odd angles ) ...often get cracked and need replacement ...the motor idles like crap with this fault

if you do a "search" in the forum propper you will find many threads about all these possible faults

but by far the best thing to start with is to get some deoxit and clean up all connectors throughout the system

oops renez covered some of these already

Thanks for your replies. The fuel filter is in the right way. The fuel pump relay wasn't sending power to the pump.A replacement cured this. The old fuel pump had seized and ,I suspect,took the relay with it. Before replacing the pump and filter I gave the tank a thorough clean out. I was careful to connect the airbox correctly,though I'll double check tomorrow. The injectors spray fuel when the engine is turned over but weather it's enough I wouldn't know. They all disperse the same amount as far as I can tell. The fuel pump runs when the engine is trying to run and, when the engine stops running after a couple of seconds the pump stops,so I figured the pressure regulator was operating and stopping the pump. I checked and cleaned all the electrical plugs whilst I had the tank off. Thanks for your points Charlie. I'll check them out and browse though the rest of the forum. Many thanks. John

john the presure regulator maintains the system presure ...not the pump ...the pump has the ability to go up to 60 odd pounds of presure should the flow path get blocked a really rich smell from the exhaust and plug fowling would be likely under this sceario

good to hear that the pump is running all the time till it expires

i would be measuring the voltage getting to the pump whilst running after hearing about the relay going faulty ...if low check the tank power connection (use a couple of aligator type clip leads to get test points outside the tank )

I have come across this same issue on another forum and the cause was badly split and leaking throttle body rubber connectors letting a heap of air into the system after the Mass Airflow sensor causing a very lean situation. Check all the places that air can get into the intake system including the crankcase PCV tube which is at the back of the plenum chamber and goes to the crankcase breather via a Z shaped tube about 3 inches long. One of the dead give aways is an oily mess there.

Maybe relevant when you did oil change have you tightened oil filler? or is the washer missing as it sucks the guts out of it when loose ( well mine did )

Many thanks for your replies on this topic.

Today I checked the fuel return to the tank as good.Took the airbox off and checked the crankcase breather and the vacuum hose to the pressure regulator.Whilst the airbox was off I removed the air monitor to check it.Found the flap was seized and applied loads of WD40 and got it moving real sweet.Reassembled everything and fired it up.Now running perfect so it looks as if the air monitor flap was the problem.Thats the first time it's been running for 5 years!.

Very many thanks for your support on this matter.Oh and the voltage at the tank connector for the fuel pump was 11.43volts.

Best wishes to all.

John

Good one! Have fun with it, they're worth a bit of TLC.

Next time you are in there you probably should put some alternative lube on as WD40 after a while does not leave much lubricating residue.
Regards,
K-BIKE

aye! ...excellent suggestion k bike .

good finding there john ....

enjoy the riding part ....yahoo !!!!