Lots of vibration, any ideas why?

[Anonymous]

I would appreciate some opinions on this subject.
I'm getting lots of vibration over 3000 rpm in my 81 GS 650 GL. I sure feel it in the seat, pegs and handlebars (obviously these are the points at which I am in contact with the bike).

The bike has 60,000 km (37,000 mi).

I have:
- sync'd the carbs twice
- set the valve clearances
- tightened all nuts/bolts on the bike
- replaced the grips with new foam ones
- cut off the original exhaust just behind the driver's pegs and replced with slip-on megaphone style (original ones rusted out)

I have not:
- balanced the tires (not until I replace them)
- cleaned the carbs since I've owned it (1 yr)

I know the compression is getting down a bit (125psi on all 4), but the bike starts, idles and runs pretty good.

I've read a few of the vibration posts saying that some of the GS models are just notorious for buzzing.
Should I accept this as normal or is there other things I could be looking into to smooth it out?

Your suggestions are welcome.

[Anonymous]

Sometimes it can be as simple as low tire pressure. Check to make sure it is up to spec and make sure none of the balance weights have come off. This happened to me once and I noticed the vibes big time.
GY

[Motorcyclemodeller]

I agree you probably lost a weight somewhere along the line, get them re-balanced and remove all doubt. Also bad steering head bearings can also cause bad vibes.

Hope this helps,

8) Andre 8)

[Anonymous]

Also, put a wrench on all of the motor mounts. If you have a book torque them to specs. Very often it`s the little thing overlooked that causes the problems.

[1100ED]

if you are sure it is a function of rpm then it will happen at 3K in any gear. that would mean it is the motor then.. First see if it is not related to speed--then you can look at the wheels etc.

[Anonymous]

Thanks for the replies.

I haven't had a chance to ride it again since I posted, but I will today. I have a feeling it is motor related because the vibration starts above 3000 rpm, regardless of the gear or speed.

Maybe I got cheap slip on exhaust?

I'll take it for another spin and try to provide more detailed info.

[Anonymous]

Sorry I haven't replied in a while.

I am now certain that the vibration is either engine or exhaust related. I have ruled out it having anything to do with the tires or frame.

What besides carbs out of sync would cause vibration in the engine?

Does anyone with slip on exhaust have experience with vibration as opposed to stock exhaust?

I have checked every nut, bolt and fasterner on the entire bike. Maybe their too tight?

I am out of ideas.

[cbxchris]

clutch hub?? loose front sprocket? Loose rear sprocket? engine mounts loose?? have you removed stock bar wieghts? skipping on one cylinder? Can`t think of anymore at the moment.

[cbxchris]

Wheel bearings? warped brake disc? 8O

[Anonymous]

It is a shaft drive so sprockets are out. Engine mounts are okay. It looks like the stock bar weights were in there when I changed grips.

The bike doesn't seem to miss. I don't know about the clutch hub, I've never been inside to look. The most I've had off the engine is the valve cover to check the valves and replace shims.

Like I said before I really don't think its related to the wheels/tires/frame at all since it seems to be rpm related regardless of speed or gear.

I do appreciateyour thoughts, it helps to have another opinion.

[Don Lobacz]

A plugged main jet, a bad carb boot/o-ring, a malfunctioning pickup advancer, a bad spark plug cap would be guesses not yet mentioned.

[Anonymous]

One thing I know has probably not been done in a while is taking the carbs off and disassemble/clean them.

Maybe there is something going on in there.

I just don't want to take the bike out of commission right now in the middle of summer. But I guess if I want to find the solution to the problem...

I don't know what a pickup advancer is, but I could check the plug caps/wires.

I sprayed WD-40 around the carb boots and there was no change in idle.

Thanks again, this is exactly what I need, fresh ideas.

[Don Lobacz]

The pickup advancer is a centrifical unit attached to the ignition pickup rotor (where the points would be if you didn't have electronic ignition). The rotor mechanism spinning on the crank advances the ignition timing as RPMs rise. You should be able to lightly turn the rotor (the smooth cylinder with a raised notch) with 2 fingers against a light spring tension and it should snap back. If not, the mechanism and rotor may need lubed.

[Dink]

After a very thorough carb cleaning get the carbs synched , if that doesnt help look at worn cluych plates or springs.
Dink

[Anonymous]

WOW!

Thanks for all the advice. Its great of everyone to take the time to throw an idea at this problem.

I sync'd the carbs last week, but that probably doesn't mean much if something is plugged or gummed up in there.

A carb cleaning seems to be the next logical step.