Low compression By kymcove21 (Read 1,781 times)

[kymcove21]

Well...... The issue was the wrong plug on why the tip was white. Secondly, she sounds like she's running fine and hitting high rpm's but the performance (speed and quickness) are still not there. So your saying that I have to electric start for 5 seconds to get the reading? Wish small engine and scooter shops didn't charge an arm and a leg to work on these things.

[Bashan]

I posted a link on how to do the test in my previous post. It's much simpler to read it.

[kymcove21]

Couple of questions, first why do I need to electric start on a compression test? Wouldn't the pressure build in the engine regardless to a point where the engine can't hold anymore? Secondly if I open to full throttle when starting i will flood my engine and carb. How does that make any sense that I have to use electric start which builds pressure similar to kickstart and I have to keep the throttle open? Just looking for some explanation here... Thanks!

[kymcove21]

Hello all. After first compression test I got to 150psi. Second test I added a tiny amount of oil in through spark plug hole and got to 190-210psi. Also posted is the picture of the engine code. Please any input on what's going on will help.

[Alleyoop]

To get a good compression reading you have to allow the motor to get as much air as possible and that is why you hold the throttle wide open. Otherwise the compression reading will be low due to not much air to be compressed which is what your attempting to find out if there are any major leaks.

Just an F.Y.I 150 PSI is very good and your motor is healthy. The reason it went up with a little bit of oil in there is oil seals any little leaks around the rings.

And yes that motor is a version of the 139QMB motor and parts are interchangeable.

Seeing as how it has good compression I would look at the CVT for the problem of loosing speed, weights are worn, belt is worn etc..