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Compression check numbers

  • Thread starter Thread starter dennisht
  • Start date Start date
D

dennisht

Guest
1980 GS750E 16 valve Speedo shows 26k (don't know if this is correct) Took compression check/test today on warm engine, all plugs out and throttle fully opened.

#1 = 175 #2 - 145 #3 - 150 #4 - 175

Any message here? Forgot the percent of difference in numbers that is ok before trouble. Any experience out there on these numbers with you GS 750 bike mechanic's?

Thanks,

Dennis
Oregon
 
Did you adjust the valve clearances first? If you didn't it doesn't mean much.
 
check your valve clearance, adjust, then do another compression check.
 
Jeez guys, dumb me, forgot to do that. Valve check is especially needed since I have no history of bike, just that it was really neglected. Thanks for the quick answer. Will do valve check tomorrow and get back with new compression numbers if they still show a difference.
 
Without the valve clearance check, those numbers don't look all that bad.

I appreciate the fact that you mentioned "warm engine, all plugs out and throttle fully opened".

You say you don't have any history on the bike. I am presuming you mean the maintenance history, how about the riding history? If it hasn't been ridden somewhat regularly, or recently, the cylinder walls might not be in prime shape for the rings to seat against, resulting in lower numbers.

Adjust the valves, change the oil, do any other maintenance necessary, then ride it for several hundred miles and check the compression again.

.
 
Thanks Steve for more information on what to do. Bike would win award for ugliest and worst appearance for sure. It has sat for several years (I think outside) not being ridden. I bought it to make into a cafe racer type bike since to put it back to all original would not be cost effective by a long shot. It had the main things I was looking for: cheap ($300), clean title, no frame or fork damage, great condition gas tank, smooth & quiet & strong & no smoke what so ever running motor and tranny shifted great up and down. The rest of the bike will not be used. Plus I needed a winter project to keep me busy. Had done a Honda CB750 Cafe Racer before so I know what I am in for. Had a knowledgeable friend clean carbs for me and replace necessary parts. Bike runs great without a hick up. BUT, since no air filters on (am going to use pods) it craps out at 4500rpm and has to have choke (enricher) on in order to run good. I will be changing clip position on needle, increasing sizes on pilot jets and main jets to overcome this running condition. Will keep you posted.
 
Dennis, those carbs, if stock, don't have adjustable needles. You will need to buy a Stage 3 jet kit & the APE or K&N pod air filters if you want to do it right. Ray.
 
Thanks Ray, the carbs are stock and I did not take them apart to see the needles so just assumed they would have the slots for richer, leaner adjustments. Looks like the Stage 3 will have to be done.
 
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