Question1982 Suzuki GS 650G bought new with 70,000km missing badly up to 3500 rpm (lurching) and fouling plugs (oily black). Bike was running great last fall when put away for winter and OK on start up with problem developing very quickly. Carbs and ignition seem OK but 2 outboard cylinders test around 90psi compression. Otherwise the bike is in excellent condition and I love it. Would love to keep if practical to correct the problem. Suzuki dealer won't touch the bike due to age but says it sounds like rings have failed.
AnswerBob, with compression that low, it probably needs a full valve job, with guides and piston/rings after a bore job.
If you have access to a leak-down tester, that would tell you just the source of the pressure loss.
If you have lots of oil smoke coming out the exhaust and excess crankcase pressure pumping fumes into the airbox, then the rings probably need replacement.
I would check the valve clearances first, to see if there are tight ones. If all clearances are within specs, then the top end has to come off for repairs. Not only do you have to consider the cost of pistons/rings/reboring and a full valve job, the camchain tensioners and rollers are probably needing attention. Add in a gasket set and seal kit and you are in it over $1,000 easily, probably more towards $1,500, depending on shop rates, parts availability, etc.
When you put it away for winter, perhaps valves on the 1 and 4 cylinders were opened and moisture got into the cylinders causing the rings to stick and/or valve seats to corrode.
Once the top end is off, you will have to check the condition of the carburetor intake manifolds, adding to the parts bills. Some of this stuff may be obsolete and not available, so I would check parts sources first, before yanking it all apart.
Bill Silver
