Compression Test

[Dragmeistr]

I know that this has been brought up previously, but I am at a loss. I have an '03 CR250 and did a compression check on it last night. It only read 100 PSI. I re-ringed the Wiseco piston prior to my last ride and did not have the guage at the time to do the check. I opened the throttle all the way and cranked the thing until my foot hurt. The most I could get out of it was 100 PSI. I know that my cylinder and rings cannot be that wore out. Am I doing something wrong? I did leave my silencer plug in when I cranked it, but that should not affect compression right? Your thoughts and help are appreciated.

 

[marcusgunby]

Im guessing a faulty guage -try taking the plug out and do another test

 

[Studboy]

If you can't get air in and out, I think that it will affect the compresion reading. If not, I would look at your gauge. A 250 would be pretty weak with that low of compression.

 

[gwcrim]

How long was your ride? Did ya take it easy for a while to let the ring seat?

 

[A-RustyDemon]

Are you saying it runs with 100 psi reading on your gage? Pull the silencer plug and try it again. If it is running and your still getting the 100 psi reading, check for carbon plugging up the intake in the gage and test it with another gage that is know to be in good working order. Because it should not start if your only making 100 psi.

 

[TRAIL]

it shouldnt kick start with 100PSI i dont think

 

[Dragmeistr]

I pulled the plug out and tried it again. 100 PSI again. I know that the guage works ok, I used prior to this on my dragster. 12:1 pistons was reading right around 180 PSI, so I know the guage isnt that far off if any at all. Funny part is the bike starts first kick, and runs great. I outran an 01 CR and an 02 KX on the long straight pretty handily. Mysteries of the universe I guess. I will just put my usual 20 hours on the bike and have everything check everything when I rebuild it again.

 

[marcusgunby]

Also how about trying it on a friends bike as a comparison.

 

[Dragmeistr]

Good Idea....Thanks for all of your help fellas.

 

[jmics19067]

is there a lot of change between a cold test and warm?

 

[marcusgunby]

a small change from hot to cold.

 

[Studboy]

There is no way that you are smoking 02 KXs and 01 CR's with 100 PSI!!! So....you must be getting an inacurate reading.

 

[cr25096er]

wouldnt a 12-1 compression ratio be higher than 180 psi?

 

[Dragmeistr]

I would depend on your deck height, chamber CCs etc.

 

[speedfrek]

Hook your compression tester to your air tank and see how far off it is from your air compressor gages