I am a new member of this site although I have been lurking for about 1 year now. Last week I purchased a 1994 TRX300WD. It is a clean looking unit from the orgininal owner. He seems to have used it mostly for yard work including snow plowing. I changed all the fluids and cleaned everything up and everything looks good. Last night I finally ran a compression check and repeated measurements read like this: Cranking the starter brings the compression up to 75 psi where it levels off. Stopping and restarting the cranking raises the compression from the 75psi to 105psi. Squirting oil into the cylinder increased the compression to about 85psi. What does this mean? The ATV starts extremely easily (even without the the choke) and runs great without smoking. Also, the kickstarter kicks hard without using the compression release but it possible to kick it over without using the compression release. I have not performed a valve adjustement yet and plan to do so this weekend. Can anyone help interpret the results? Thanks, Brett

 

On a fresh engine, you should get around 140 psi (I believe it is a 10:1 system) - measured cold with the throttle held wide open (this gives the highest volume of air intake). Your highest reading was 105, which means it can produce 105, even though you got the 75 & 85. Oil only boosted you 10 psi, so your rings are not that weak.

IMO, since it does not smoke, and starts and runs fine, I would check your valve adjustment and then leave this issue for a later date and time when things are not working properly.

 

Ujoint's reply reminded me that the throttle needs to be held open when running the compression test. With the trottle held open it reads a little over 180psi. Mystery solved. Thanks! Oh, and the valve adjustment showed them to be a little loose.