I just finished rebuilding a 1980 GS750L. After having the head trued (it was warped so the machine shop took off about 0.024in. - mostly from the outside parts of the head) I put the engine back together using two head gaskets. I did a compression test, which was rather low and I noticed the two center cylinders were 20 lbs lower that the outside two cyls., i.e., 110, 90, 90, 110. The bike starts fine, and runs very well over 4,000 RPM. But, it seems rough from 1,500 to 4,000. Plugs look normal, bike idles fairly well, acceleration is fairly quick and smooth, top RPM obtainable in 1st & 2nd gear, compression does not drop with time so I feel rings and valves are OK. Maybe I am being picky, but I want the bike to be smooth at all RPM ranges, especially during the low to mid range.
So ? my question: what should I try first from the list below and in what order (or do you have another suggestion not given)?
1) Should I be worried about the low compression reading and the difference between the cyls. or the fact that so much was removed from the head (it is over the recommended amount of 0.009in.) and install another head?
2) Should I remove one head gasket in an attempt to get the compression up and see what that does?
3) Should I synchronize the two center carbs with a little more vacuum gauge reading since the cylinders are not ?pulling? as much compared to the two outside cylinders? Has anyone ever synched carbs relative to their respective compression reading?
4) Should I raise the jet needle slightly more on the two center carbs (giving them a bit more gas at mid RPM)?
5) Should I even give a crap and just ride the hell out of the bike for the next 20,000 miles?
Thanks for your opinions. I know just enough about ?mechanen? to get into trouble, but not enough to get out!
Paul C.
So ? my question: what should I try first from the list below and in what order (or do you have another suggestion not given)?
1) Should I be worried about the low compression reading and the difference between the cyls. or the fact that so much was removed from the head (it is over the recommended amount of 0.009in.) and install another head?
2) Should I remove one head gasket in an attempt to get the compression up and see what that does?
3) Should I synchronize the two center carbs with a little more vacuum gauge reading since the cylinders are not ?pulling? as much compared to the two outside cylinders? Has anyone ever synched carbs relative to their respective compression reading?
4) Should I raise the jet needle slightly more on the two center carbs (giving them a bit more gas at mid RPM)?
5) Should I even give a crap and just ride the hell out of the bike for the next 20,000 miles?
Thanks for your opinions. I know just enough about ?mechanen? to get into trouble, but not enough to get out!
Paul C.
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