Is 110psi too low for a cold engine? 89 KX250

**crispy** · 9th March 2014, 09:00

Hey all so when I first bought the bike about 10 months ago, (maybe more) It wasn't running due to a spark issue. While it was playing up i decided to do a cold compression test on it. This was 175-180 psi. Now that I've had it running and riding it a couple of times the compression test has come back at 110-120 psi. Bearing in mind the bike hasn't really had a lot of riding, twice on gravel . once being over xmas holidays and it played, up didn't start after I stopped it. Then last weekend out at Mcleans island for an hour or 2, ran like crap thanks to my s2% fuel I was running. In my mind the fact the compreesion is lower says to me this woud cause hard starting. Any ideas from people?

**Akzle** · 9th March 2014, 16:27

i view compression as more of a yes/no thing. So id say your shits fine.

**crispy** · 10th March 2014, 05:26

Ok, just kicked it over yesterday on the first kick it kicked back, 4th kick it fired up. The issue I have is being the engine has unknown history, other than looking through the exhaust and intake ports inspecting the piston and barrel and giving it a compression test, is when it's warm or been sitting after being run it's a bit hard to start. I thought this was due to engine wear or maybe a float issue. (I did clean the carb out reset the float to factory spec (15-17mm) and now it's got this issue. I thought I may drop it to where it was (19mm) which when it was like this, started on third kick with choke after sitting for 5 minutes.

**Akzle** · 10th March 2014, 05:59

a small 250 kicked back?
You need to work on your technique. Youre probably flooding it.
Dropping the float may lead to starving when youre doing wheelies at wot

**Akzle** · 10th March 2014, 06:09

5 minutes wont cool an engine, you shouldnt need any choke to re start it.

**F5 Dave** · 10th March 2014, 16:35

Originally Posted by Akzle

a small 250 kicked back?
. .

Not much time on motocross bikes huh?

**F5 Dave** · 10th March 2014, 16:37

Ignore compression readings, they are virtually bull on a 2 stroke. You only need some oil puddle (common) to throw up the bore when kicked to root your readings.

Those carbs wear (watch slide & emulsion tube can ovalise) and need a clean out if sitting (pilot etc), but always a new plug when in doubt even if old one sparks in fresh air doesn't mean its good. Powervalve can be an issue on these but this won't affect starting really.