Please Help The New Guy!

[deckard26]

My 1985 GS650GTZ is driving me nuts! Runs fine for about ten minutes then just dies. Feels like its struggling first, then power falls off and it starts to chugg, then dies. If I leave it for ten minutes or so it will normally restart but wont run for very long without cutting out again. Have checked fuel line,plugs and carbs but cant find anything wrong. Only thing that I can think it might be to do with is I started to hear the front disc brake dragging as this started at about the same time. Would this cause the engine to overheat and shutdown? Only had the bike four weeks and I love it, but need it for work so need to sort it out quick. Hope someone can help. Kevin.:???:

[tfb]

G'day Kevin,

Take it for a spin and when it starts to die, pull the choke on. If you get a momentary lift in performance before it dies, you have a fuel starvation problem for sure. From the sound of it this is your problem, but give it the 'choke test' to make sure.

If it is fuel starvation, check the following:
1. Clean out your tank and fuel tap if you haven't done so already.
2. Drain your carbie float bowls to make sure there is no backlog of rust sediment etc. blocking your jets.
3. If you have an inline filter, throw it away. They can easily cause 'vapour lock', a common problem in gravity-fed fuel systems. Besides, an inline filter is not needed as there is already a fine nylon gauze mesh as part of the fuel tap assembly.
4. Check and clean the vent that is inside your fuel tap. It may well be that you are not getting enough air drawn into the tank as your bike is using fuel.

See how you go with all that, and get back to us with a progress report!

[deckard26]

Still Driving Me Nuts

Removed the fuel filter and replaced the fuel line.checked the petrol tap and the carbs.Idled fine when I started it, took it for a spin, still seems slugish. Did about half a mile and it cut again.Revs raced up and then it died, choke had no effect. Restarted and then revs kept going high and then died again.Any ideas?

[chef1366]

Do you have a vacuum activated petcock?

[KEITH KRAUSE]

Sounds like two problems.
Clean out the gas cap venting. Classic poor venting symptom is a bike that will run for a short time but the lack of adequate venting will soon starve the motor for fuel. Can get worse with outside temps rising. Wait a little and the bike will run OK again for a short time. Easy to check and clean.
Your other problem sounds like an intake leak. If the bike idles significantly higher from cold to hot, it's an intake leak almost certainly. Most likely your manifold o-rings (if your model uses them) or the manifolds themselves. You may be lucky and just have loose manifold clamps or the carbs aren't "popped into" the manifolds correctly.

[deckard26]

Do you have a vacuum activated petcock?

THink so, not sure to be honest. How would I know?

[deckard26]

Sounds like two problems.
Clean out the gas cap venting. Classic poor venting symptom is a bike that will run for a short time but the lack of adequate venting will soon starve the motor for fuel. Can get worse with outside temps rising. Wait a little and the bike will run OK again for a short time. Easy to check and clean.
Your other problem sounds like an intake leak. If the bike idles significantly higher from cold to hot, it's an intake leak almost certainly. Most likely your manifold o-rings (if your model uses them) or the manifolds themselves. You may be lucky and just have loose manifold clamps or the carbs aren't "popped into" the manifolds correctly.

Ok, thanks. will have a look and let you know if it sorts it out. Thanks for the help.

[chef1366]

You'll have two lines coming out of your petcock. One to the engine and one to the carbs.

[deckard26]

Yes, I do. Took petcock apart, everything semms clean. removed inline filter, fitted new fuel line and cleaned vents in petrol cap. Still got same problems, any ideas?

[KEITH KRAUSE]

Intake leak is the most common cause of a high idle once warmed up. It could be a throttle plate or something mechanical in the shaft that connects the plates but it's probably an intake leak. The intake leak could cause the bike to stall.
If you also have a fuel flow problem and you suspect the petcock, try turning the lever to PRIME and test. This will bypass any failing petcock diaphragm.
If the petcock is good, I think the passages to the float chamber(s) or any screens above the float needle valves is partially clogged. Or you could have some sticking/varnished float valves or floats, but you said you cleaned the carbs or just checked them?
Also, how much fuel is in the tank? Enough to run on the ON position? You may be near reserve level?

[83GS750E]

Sounds like

not sure not a real bike repair expert, but if your bike runs for a lil while then stalls sounds like your bowls on your carbs aren't getting the fuel, your jets might be sticking. after it stalls turn it to prime n wait 2 mins or so let them fill up and try starting her again if it fires and runs for 5 mins or so, then you might wanna take another look at your carbs.

[Planecrazy]

Don't know if this applies to the 650's, but I've heard that on '80 550's there is a vent tube coming off the carbs that can cause this sort of problem. Some people have removed that tube and the problem disappears.

Good Luck!

[deckard26]

Ran it until it cut again, then opened drain screws on all four carbs straight away to see if they where empty but they are full so I think the fuel is going through. Also removed the tube like planecrazy suggested but that didnt help either. Did notice that when tap in primrary position no fuel appears to come out.So set to reserve at the moment.

[nabrams]

Sounds like you've eliminated the usual suspects.
So that leaves the electrics. Failing electrics (coils, igniters, charging components, etc.) can run fine till they heat up and then they shut down. I (and others) have had this problem. Your charging system may have a short that heats up after a bit and robs all your juice so that bike won't fire the plugs. So detach the charging system, headlight and tail-light (your bike will run for several hours on a fully charged battery with lights off) and see what happens.
Another thing to verify at the point of failure: Visually verify spark (immediately after the bike dies). Of course, you'll need to carry the necessary tools on the test ride. Now, if it won't spark at that point (with the charging system having been detached and a fully charged battery before the test ride), you'll know for sure that either your coil or igniter is the culprit. If both coils won't fire then it's almost certainly an igniter problem. If one will fire but the other won't then it is a coil problem or a poor/corroded connection in the wiring leading to that coil.

[deckard26]

You where right, CDI unit is corroded and burnt out. Trying to get new one now. Thanks everyone for all the help. Much appriecated.
Regards
Deckard26