[roger777]

I just bought a 150 yamaha sx150xtra and did a compression test.. 99-100 on all 6. The way I was taught to take test was to pull all wires from plugs so motor doesn't start then break all plugs and one at a time pulling, test and replace plug. I here some people start the motor instead of pulling wires so it doesn't start.. Is either way the right or wrong way? Pros and Cons? Would my comp. test have been higher if I didn't break all the plugs before pulling off 1 at a time.. I hear 120-125 readings on these motors.. Just want to make sure I dont have low comp.
Thanks

[JB]

Correct procedure is to remove all spark plugs, Roger. The ignition can be disabled by pulling the kill lanyard or by simply leaving the key in OFF and operating the starter with a simple jumper at the solenoid.

Actual readings vary a lot because of differences in guages and technique, the important number being the spread of readings among the cylinders.

I would accept the readings you got as a healthy engine because you left the plugs in. With the plugs out you probably would have gotten readings a bit higher.

[roger777]

Thanks JB
I am going to pull all plugs out just to see if the readings are higher..
Roger

[rodbolt]

correct procedure will also ask for a WOT condition and the engine at operating temp.
however like JB said what we are looking for is consistent readings with a consistent test pattern.