... not mention feeling pretty stupid at this point.

I spent much of the winter working on the GS: new jets, progressive springs, katana rear shock, valve adjustment and a million other little things. Everything thing I did made a noticable improvement, easy start and quick warmup, way better suspension, but something was missing. It didn't have any giddyup, no get up and go when I twisted the throttle.

Note that I don't think it was any worse than before I worked on the bike. This is primarily my wifes bike so I hadn't ridden it much and have only vague memories of how it ran before.  I guess I thought that the rejetting would have also made it peppier.  Its certainly ridable, and I can get up to freeway speeds of 85mph, but there's no reserve power left in the throttle.  I don't think I'd be comfortable making a pass on a two lane road.

So I did a compression test on the bike after it was warmed up. The numbers were 140/145, basically at or below the bottom of the specified range.  I then added a squirt of oil into the spark plug holes and tested again, 165/165.

So here are my questions. BTW, its a '93 with 25,000 miles on it:

1.  Are my symptoms consistent with those compression numbers, or should I be looking at something else?

2.  The manual says that if the compression rises a significant amount after adding a teaspoon of oil, that means the piston rings are probably worn, as opposed to a problem with the valves.  Does my increase after adding oil constitute a "significant amount", thereby making the piston rings the suspect component? Or does it still need a leakdown test?

3. How hard is it to replace the rings, or how much would a repair shop charge for such a job?

4. Anything else I should be checking?

I'm bummed that I put all that work and money into a bike that may still need some major work. I feel stupid for not having made a compression test before doing the work, or even before buying the bike.

u think u got it bad my compression is alot worse, without oil it's bearly 90 with oil in both cylinders it's just under 100, i think i need an overhaul nooo and to rehon the cylinders

Forgot to include the following info, that may be relevent:

Pilot jets: 40, Main jets: 125, One washer, Air screw: 4 turns out
Cobra slip-on exhaust
Stock air box with UNI foam air filter

No leaks at the intake manifolds. Little vacuum o-rings on top of carbs in place (new in fact). Valves adjusted.

Question to mayz2010:  How does your bike run at that compression level, or does it?

bit sluggish when i crack the thottle open and at low rpm, once i get to high revs and speeds doesn't pull aswell struggles to get to 108 and i know i get faster. but i'm doing a engine rebuild soon so i'll rehone it then and get some new piston rings and then do a nice FAST break in not what the manual say's break in, hope that helps what symptons do u have.

Pretty much the same symptoms as you. No real power at any RPM. Pulls like a scooter.

40K miles and I make 155 or so hot in either cyl... the 7K 91 also made ~ the same... test it hot and test it with the throttle WFO. Mine does have decent power... but its weaker than the 91 and both the 91 and the 89 are weaker than my 90 was... 1700 miles to 6K miles was when I had it.
Cool.
Srinath.

ok i need an overhaul and my bloody rev counter went just as i looked at hit 8000 rpm and then justwent to zero, while doing a group ride today.

Your tach cable may have just come loose.

Srinath and I had fun fighting over his high mileage turd.  compression was the same as mine.  but you really need to warm it up to get proper clearences for a true operating compression ratio
also either remove carbs or WFO to get as much air as possible in there

he kept telling me his rings were shot and that was the cause of oil consumption.....
more likely bad valve oil seals after 40k...

140 isn't too bad. Shouldn't make the bike noticably more sluggish, especally if all you did to the motor was rejet and valve clearance check.

Now did all you do is check the valves or did you have to change any shims? If you did change any shims did you do them with the cams in place or did you dismount them? Are you positive you got the valve timing correct?

If you do have to redo the cylinders, you can look at it as an opportunity to bump up your displacement a bit. With 25K on it I wouldn't try to just replace the rings, there may be too much of a gap.  Its fairly easy to order 1mm or 2mm overbore piston kits from Suzuki (but they cost a bit).

The high mileage turd is a 1/2 decent bike once you get it going... It is down on power on the 7700 mile one... but its oil useage isn't that high once you dont do long distance runs... I now only make ~ 12 miles at a time... and its oil useage is down drastically. Its got tons of blow by and quite a bit of valve seal leak... and even a little leaking out the alternator cover, but hey I aint fixing it... its cheaper to clean the driveway... Just kidding... Once I locate a starter clutch... I'll do it all at the same time.
Cool.
Srinath.

GEE, I might have one of those....check to see if a GR650 one will swap....but the starter clutch and get the rest of the engine for free
:mrgreen:

OK off to biker bandit I go...
Cool.
Srinath.

Replying to questions from several different posters. Keep the ideas coming.

My compression test was done after a 5 minute warmup ride, not a very hard ride.  Would a 20-30 minute ride make a big difference? I discovered that I've got to rebuild the front brake caliper due to a leak and didn't want to ride too hard if I couldn't stop.  

It was done with WOT.  Should I remove the airfilter to get more air. That was not mentioned in the manual.  Should choke be on or off or no diff.

If you don't think 140/140 is that bad, what else could contribute to a general sluggishness?

I replaced my fuel hoses with 1/4" ID hose, which is just slightly smaller than the stock 7mm.  Any chance that could be the problem?

One valve was too tight and I replaced the shim with valves in place.

I had reoiled the foam air filter. I don't think I did, but if I oversaturated it, what would be the symtom?

Are gel seats slower than stock seats? :lol:

think i have one wired together as a set, gear and sprag set, little surface rust but nothing major, fact i know i have one on a crank that spun a bearing just got to yank it.

Say what???

Quote from: joefromsfSay what???

He's talking about the starter clutch from 2 Srinath posts back.

If you oversaturated your oil filter you should be running rich, and your spark plugs should look a bit dark - or even wet.

Thanks Kerry.

Spark plugs look good, light tan.

Quote from: joefromsfReplying to questions from several different posters. Keep the ideas coming.

My compression test was done after a 5 minute warmup ride, not a very hard ride.  Would a 20-30 minute ride make a big difference? I discovered that I've got to rebuild the front brake caliper due to a leak and didn't want to ride too hard if I couldn't stop.  

It was done with WOT.  Should I remove the airfilter to get more air. That was not mentioned in the manual.  Should choke be on or off or no diff.

If you don't think 140/140 is that bad, what else could contribute to a general sluggishness?

I replaced my fuel hoses with 1/4" ID hose, which is just slightly smaller than the stock 7mm.  Any chance that could be the problem?

One valve was too tight and I replaced the shim with valves in place.

I had reoiled the foam air filter. I don't think I did, but if I oversaturated it, what would be the symtom?

Are gel seats slower than stock seats? :lol:

Ok compression test after a good 20 + min ride... 5 mins woint even get it hot enough to warm your toes... especially in SF in winter/early spring. Also screw in compression guages are better than those conical press in rubber boot thingys... Fuel hose... right size id very important... wont affect compression but running yes... especially high speed... The bike has enough fuel flow resistance wihtout you adding to its woes.
Tight valves will eat compression... but in 1 cyl ... you might still be at 140 in the other... = uneven = bad.
Air filter over oil wont affect much... might smoke a little in the first 1000 miles or so.
Cool.
Srinath.