Bad Stutter

[Anonymous]

I have a 1981 Suzuki GS750 and just recently it devoloped a bad stutter. It will only do it in 4th and 5th gear on the highway. As soon as i pull the clutch in it will idle and rev smoothly and in 1 2 and 3rd gear there are no problems. I have checked all my fuel lines and have takn the carbs off and cleaned them and the problem is still the same as before. I am not sure what else to check. Is it possible that it could be an electrical problem? i am stumped

[flyingace]

I don't see how the gear you are in could make a difference unless it's a transmission problem. Besides that, I don't know what a 'stutter' is. Do you mean the engine misfires?

If so, see what RPM you are at in 4th gear when it misfires and run it to the same RPM in 3rd or 2nd gear. Does it misfire then?

Ace.

[Anonymous]

At what rpm and or speed? CV carbs tend to have slight flat spots. When was the last time you pulled the carbs and cleaned them?

[Anonymous]

Mabe it is more of a surge than a stutter....it will accellerate smoothly through the first 3 gears and i can get the bike going 120 kms pretty easy but when i shift to 4th and 5th it begins to surge. I can usually hold my speed near there but it will not accellerate past. When i shift down the problem seems to go away. I took the carbs off and cleaned the main jets and float boals out but nothing changed. The carbs didn't look dirty at all to me.
still confused

[flyingace]

It sounds as if your bike is struggling to pull against the wind at high speed. When you shift down, it's more in the power band and it runs OK.

This could be a lot of things. Is this bike old and tired - do you know its compression readings? Is it starving for air - as in the air filter needing cleaning? It doesn't sound related to carb or ignition since everything is OK in lower gears.

[Anonymous]

Well.....I tested all the spark plugs and found a 2 of them to be putting out a really weak spark so i changed them again (i put new ones in about a week ago) and now the bike seems to run alot better although it does misfire or surge every once in a while which is much better than all of the time like before and now the bike seems to have alot of the power back. I would still like to get that bit of surging out though. It does not seem to have a pattern to it....it will only do it at high speeds and misfire for a bit for a bit then will be fine for a long time. The last time it did it i just let it misfire for a bit then shut it off quick and felt the exaust pipes and the one on the number 4 cylinder was alot cooler than the other three.
Just came to mind too....when i had the carbs apart i did notice the number 4 main jet was a slightly different jet than the ones in the other carbs. I don't know if that could make a difference since i bought the bike last summer and rode it all summer without a problem.

any thoughts?

[Anonymous]

make sure all the jets are the same, one cylinder running too lean can cause interanl engine damage. Sync the carbs after your done with them. Also, lose the paper filter and install a K&N filter. one other thing, check the (CV carbs) carb slide diaphragms make sure they are working right. one little pin hole and they are trash. Might look into some new coils. OEM coils tend to break down with age, I put some accel coils on my bike and felt a huge difference.

[Jethro]

Been through this. Here is my suggested check list:

1. Take the bike out and make it stutter or surge. Pull the choke during it and see if that improves it. That tells you if it's a lean condition which may be caused by an intake leak or a patially clogged main jet, etc.

2. Check your float heights and make sure the floats are still buoyant.

3. Make sure the gas cap vent is clear.

4. Check for arcing of the wires. Pull the tank, attach an auxillary fuel tank and start her up in the dark. Look closely at the wires and where they attach to the coils.

5. You may have to pull the valve cover. Check that the timing chain isn't stretched. Make sure the valves are gapped in tolerance. Check the compression at some point.

6. Check the petcock screen. Got an additional fuel filter? Throw it away.

I'll add morw when they come to me.