How much compresion?

[GS750]

Was standard on a GS750B?

I would think that they would be around 190Psi when new, am I correct?

[Nessism]

Was standard on a GS750B?

I would think that they would be around 190Psi when new, am I correct?

I don't have the specs but most stock engines run less than 190psi even when new.

If you are trying to determine if your engine is still good warm it up first, take out all the plugs, makes sure the battery is fully charged, and then take the compression readings with the throttle wide open. Anything in the 150psi range is excellent. If they are lower, or inconsistent between cylinders, dump 1 teaspoon of engine oil into each cylinder and check again. If the readings come up you have bad rings. If the readings stay the same you may have a valve problem. Check those clearances. Of course, you should varify the valve clearances before checking compression if possible.

Good luck.

[ptm]

I believe new (but broken in) would be more like 165 psi or so. Per the factory manual, the lower limit is 100 psi and no two cylinders should be more that 28 psi different.

[SPARKSS]

Was standard on a GS750B?

I would think that they would be around 190Psi when new, am I correct?

190 psig would equate to at LEAST 12.9:1 compression ratio (near sealevel) while cranking IF the camshaft is only 180 deg duration approx. If it's longer duration (typical for high rpm engines), you'll see less while cranking (pump back past BDC). I'd be more inclined to expect cranking compression (unmodified engines expected to run on pump gasoline) to be in the 120-130 psig range while 100-115 psig isn't abnormal (while cranking) on higher mileage engines (assumed valves sealing ok)........look for consistency etc as others have mentioned.