Motorcycle Repair: GR650 Vibration, bikebandit com, flywheel system

Question
Hi Bill.

I have a '83 Suzuki GR650 Tempter with 4100 miles.  It has developed a high frequency vibration that I start to feel
in the bars, tank and foot pegs at about 2500 rpms.  The faster I go the faster and more intense the buzzing gets.
I feel it a bit more in the left grip and left peg.  It also subsides a bit when there is more of a load on the
engine (as when I start to go up a grade on the highway) but it is right back when the engine load goes back down.
As well when I chop the throttle to slow down there is a strong buzz.
The previous owner put engine guards on it and when I reach down to touch the left guard it feels like a tuning fork!
I use 10W-40 oil.

I don't know how to diagnose the source of the vibration.
 
Somebody mentioned a carb sync but I would think there would be other symptoms with that.

Need help Bill!

Thanks,
Pete

Answer
Pete, I had to look up info on this model, as it is not a Honda and not a model I have encountered before. Barely remembered it at all, really.

I found a GR650 forum:

http://hotel.messageboard.nl/3669/viewforum.php?f=2

I am reminded that this motor has a centrifugal extra flywheel that is supposed to kick in at low speeds and disengage at higher rpms. The engine is a 180 crankshaft design, so pistons go up and down in opposite directions. The engine has a gear driven counter-balancer shaft to offset most of the vibrations. It appears to be bolted solidly into the chassis, so no rubber mounts to deteriorate, I guess.

I would start by checking all of the engine mount bolts to ensure that nothing has loosened up there. Remove the engine guards temporarily. If the whole motor seems to be bolted in solidly, then the other systems to check are the flywheel system for the clutch and perhaps the balancer shaft. There are some gears bolted to the crankshaft and elsewhere inside, so perhaps something is loosening up internally.

http://www.bikebandit.com/1983-suzuki-motorcycle-gr650d-tempter/o/m5979  for some illustrations.

Carb synch can improve idle smoothness and part throttle issues, but I can't see it being a major contributor to massive vibration issues.

Magazines tests mention changing gearing up a couple of teeth to lower the overall engine rpms on the highway. This will reduce the frequency induced vibrations to some degree. It could be that the extra flywheel is not disengaging. Drain the oil and look for signs of metal or contaminates in the oil and filter that might indicate some internal engine issues. If it is all clean inside, then it may just be the nature of the beast.

In some cases, on some makes/models, loosening the exhaust system completely and then tighening it from the header flanges to the rear mounts can help with frequency issues, if the components are in a bind. If you find that the rear muffler mounts are not lining up with the holes and/or there are gaps between the mounts, insert washers to take up the spaces, rather than force parts into a bind.

That's all I can share with you on this bike's issues.

Bill "MrHonda" Silver