Last year I picked up a GS750 that had been sitting for about eight years. It had electrical problems, but the previous owner (who was giving me the bike for free, so had no reason to lie) said the engine ran great, but the battery wouldn't charge and he'd lose spark occasionally, so he parked it. The first compression check I did showed 90-100 psi across the board in all cylinders. The engine was cold, the rings were rusty, and it'd been a long time since the crank had seen anything over 10 rpms. It didn't worry me a bit. Once I got the bike running, I didn't worry about compression, because everything was running fine.
After seeing this thread, I checked compression on cylinders 1 and 4 last night for giggles. Both were at 140-145 cold. That reading would probably be 10-15 lbs higher hot.
I know that everybody reads the 128 psi minimum compression then rebuild thing in the manual, and then they flip out when a new bike doesn't make it there. Truth is it may never get there, but usually after running for a while, breaking the rings free and getting them reseated into the cylinders, they usually do.
Your bike has a lot of other issues that are easier and much cheaper to address than a top end rebuild to raise compression. That may or may not fix itself once you get the bike running, but the bike won't run without sorting out carbs and ignition first.
There's no point sending the dog into the foxhole if the fox ain't there.
After seeing this thread, I checked compression on cylinders 1 and 4 last night for giggles. Both were at 140-145 cold. That reading would probably be 10-15 lbs higher hot.
I know that everybody reads the 128 psi minimum compression then rebuild thing in the manual, and then they flip out when a new bike doesn't make it there. Truth is it may never get there, but usually after running for a while, breaking the rings free and getting them reseated into the cylinders, they usually do.
Your bike has a lot of other issues that are easier and much cheaper to address than a top end rebuild to raise compression. That may or may not fix itself once you get the bike running, but the bike won't run without sorting out carbs and ignition first.
There's no point sending the dog into the foxhole if the fox ain't there.
) Find your spark issue, fix it. And while you're at it, check your charging system. At LEAST check the valves, you're a fool not to. They need checked every 3k miles, anyway. If the motor turns over and you see NO BLUE SMOKE, and the valves arent burnt from neglect, and are adjusted, you do NOT need a top end rebuild. After you check your valves, clean your carbs, assure there are NO air leaks in the airbox and intake boots. Check that the head bolts are torqued down per spec. Then you should be golden. Refusing to do these things, you might as well park it back out in the yard with a for sale sign on it, or maybe it DOES make a nice lawn ornament...
