2003 KX250 compression too high????

[svttodd]

I have a 2003 Kawasaki KX 250 that suddenly started to have a strange bog off idle, when getting on the gas. Well, I checked the compression and it seemed way high (I don't remember the numbers right now). I put in a new plug and the problem resurfaced, but the plug looks clean and normal colored (I have looked at several on-line photos of 'good' and 'bad' plugs, and mine looks 'good'). Well, I took the bike to a shop and the mechanics said 'holy mackerel, your compression is really high!' They tested it again and again with the same 'really high' compression numbers. They recomended a complete tear down to lower the compression. My question is...Is there anything simple that could be causing a false 'high compression' reading? The bike was running fine, then all of the sudden got really high compression? That doesn't make sense to me, usually the compression would go lower with wear and age, right, OR... is there something like maybe the power valve or something that is stuck, dirty, etc, and making a bad/high compression reading? PS: The bike's kick starter is very hard to push through its cycle, but the bike seems to start just fine otherwise. HELP. Thanks. -Todd

 

[kshackleton]

My 2001 KX 250 has 176 lbs compression and it runs fine. I suppose that carbon buildup on the piston could cause high compression. Have you pulled the head off to have a look? Perhaps a sticking exhaust valve?

If it was me, I'd pull off the head, since that's simple...then I'd redo the top-end if there was nothing obvious. When was your last top-end and how many hours are on the bike?

 

[CBRob]

It would take a WHOLE lot of carbon to bump up compression very much.
My guess would be a clogged pilot air circuit, which you could ID by doing a plug check with the throttle cracked about an 1/8th of the way. It would help you rule out "too high compression" if you could get the actual compression test numbers, and see how close to 175psi you are.

 

[kshackleton]

I'm confused...how could a plugged pilot circuit have any effect on the compression test readings.....I am assuming from the OP that the bike shop performed an actual compression test....yes?

 

[CBRob]

I was suggesting that the compression was normal, but considered high by the mechanic. The pilot could be the culprit for the sudden bog off idle.

 

[CBRob]

If you still suspect carbon buildup, you can get a visual by removing the pipe.

 

[svttodd]

I still don't have the numbers... it was a few months ago and I forgot them since the tests were done. I will re-test to get the numbers soon. I got frustrated with the bike and I just put it aside and started riding my 2005 Husqvarna TC450, man I love my Husky...anyway... I think that the compression was around 220-240psi (!), but I can't remember the exact number. I tested it with a proper guage, and the shop tested it with their equipment. The shop owner even checked it after the mechanic because it was so high, and he was suprised.

I originally took a look at the bike because it was running fine, then all of the sudden started this nasty bog. You would whack the throttle and it would bog, nearly throwing me over the bars, then it would clear itself and the thing would suddenly haul butt and try to throw me off the back. Not a good thing for woods riding. Anyway, I thought that it was jetting, but nothing had ever changed in the jetting, fresh gas, same mix ration as always, no different weather, no new mods, plug looks nice, etc., so I thought that it was very weird about the sudden bog. I checked the compression just in case, and thats when I got the high compression. I then took it to the shop to see what they would say. The shop tried to fix it but then said that they would have to fix the overly high compression first before they could properly tune it. What the heck would make the dang compression suddenly be really high, whne nothing else is new? The bike has low hours on the motor and shouldn't need a rebuild, but I will do one if needed though.

 

[Chokey]

220-240 psi is very healthy, but not excessive for that engine. My brother-in-law's '03 tested at 220 last month, with about 2 hours on the piston and rings. My '02 usually is around the 215-220 mark. I have a friend with a '05 YZ250 that regularly tests at @ 245 psi.

 

[trial_07]

The numbers aren't important! Mechanics have been surprised by the test results so we are talking about something abnormal.

Did your bike suddenly started to bog or was that a progressive thing?

 

[jumpingjoe628]

Make sure your reeds are not broken.

 

[svttodd]

I think it was a kind of sudden thing with the bogging. It was running fine, then it started to bog on one ride, then the next ride it was really bad, as opposed to happening over many rides.