compression test 550 maxim

ok, as some of you know, i have a firing problem. my two left headers stay cold. so i was told by (one of the best)....to try compression testing first. so i baught a tester that has the rubber fittings compared to the threaded ones. tommorow after work i will attemt to test all four , i guess cylinders? anyway, i have never done this before, so any pointers would be nice. its a 550 maxim motor, strapped into a atv frame. thanks guys.

 

The compression test is supposed to be done warm. So if you left two are not firing right and warming at the same level as the other two, they are likely to have lower compression numbers than the other two.

Just wanted to mention that so that you don't have a panic attack if they come in low if tested warm. I had one that was pretty low, but I found that it was running lean at idle which was how I was doing the warm-up. Got the adjustments more dialed in, and the compression number came up.

If you test them all cold, then they should be on the same par, but you will likely get numbers below spec. May be worth doing cold to see where things are and then warm it up and check again.

Just my experiences from what I have seen. Your mileage may vary...

 

thanks joe, is there anyone else with any pointers?

 

ok, i had the bike cold, and the guage jumped up to about 70 psi on all plug holes. that sound right? as i would crank the guage would go up to 70 and down to zero...........up to 70, back to 0.

 

Ok im not sure if the Model year matters or not but I have a 81 xj550 and in the Clymer repair manual your compression test at sea level with the motor cold should come in at 121psi standard and a minimum of 100psi with a maximum difference of 14psi between cyclinders

 

Make sure you have (WOT) wide open throttle during testing.

 

so even though i dont acually start the bike, open the throttle all the way while turning it over?

 

Yep.

 

thanks amoney, and everyone else , hopefully full throttle will increase psi.