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Compression of 120psi, how bad is that?

Redman

Redman

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Working on this GS1100GK I got recently (only 28K). Compression check shows 120-130-120-140 with engine warm and throttle opened. I know that is less than normal yet above the "service limits", but what I dont know is just how bad is that? Any comments? That bad enough that it will be more like a 400 than an 1100?

I also checked compression with a couple tablespoons of oil in each cyclinder - much higher, like 170 to 180 or 190, so that tells me the rings and/or cyclinders are worn, right? Might this need more than new rings? Or cant tell untill measure cyclinder bore?

Probelm I am having is that on startup two pipes dont warm up aas fast as the other two. Pipes #3 & 4 warm up first, #1 warms up slower and #2 will still be cold when others are warm. During warm up it doesnt run smooth, boggs if try to rev up, slight back fire out exhaust while warming up. Have tried pinching off the petcocks vacuum line - no difference. After it all warms up it still doesnt rev/accelarate like I think it should, wants to bogg. All this sounds to me like carbs need cleaning.

Have looked at sparks, all sharp snappy sparks.

PO says it "hadn't been rode much in 3 years" when he got it, he had it a year, then advertised it as "ready to go". I see it has new coils and new petcock.
NovGK_auction.jpg

It looks good, but is an other bad flea-bay story.
 
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Compression readings don't seem all that bad to me. More important is how even your compression is across all cylinders.

Does that number 2 cylinder stay cool...does it ever fire? Most of the time in my experience, a plug that will fire when tested and not when its in the bike is in a cylinder that is running too rich......If its not firing, then your bike will "bog" and not run well when its warmed up.

By the way, that's a great looking bike. Hope you can get it running well.
 
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Well if it's not leaking or blowing oil all over the place then I'd ride it like it is. Cause once you crack one of these puppies open you might be replacing alot more parts too. Somethings are best unknown.

I use to say if it can make it to the stop sign down the street then it can go cross country and believe me it did.

Sounds like you might be having a bad coil on 1&4.
 
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If its been sitting up for three years, I think it would need loosening up and reseating to some extent. Internal corrosion may be a factor. Also, dirty carbs, out of synch carbs and poorly adjusted butterflies will cause inaccurate compression readings. The reading you have are not wonderful, but they are not that bad either. I suspect soaking/cleaning and rebuilding the carbs will make a major improvement and eliminate about 98% of your problems.

Earl
 
Try and pour some marvel mystery oil into all the cylinders for a few days, turning it over by hand once a day. You may just have stuck rings or carbon build up.
 
PO said it "didnt get rode much in 3 years", but that was when he first got it. It was run for the year he owned it, but dont know how much.

Marvel- Mystery- Oil. Tell me more. That stuff specifally for loosing up stuck rings?

I am wondering if "didnt get rode much in 3 years" really means "sat neglected for 5-6-7 years in a damp barn" and cyclinders rusted up, then somebody just started it and wiped the rings.

So, you guys seem to be saying that 120-130-120-140 really isnt all that bad.

I quess, since I dont have any snow to shovel, I will proceed with pulling the carbs and seeing what I find there.
Jan02_05GK.jpg
 
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It works, My neighbor resurected a 56 Chyrsler last year with it. Brought the compression up enough to get it running again and stopped oil burning
 
Carbs 1& 2 probably need cleaning ??? Check the #2 cyl for rich condition, look for fuel in the vacuum line to the petcock.
 
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