checking compression

[kilabeez0]

My compression guage came with attachments for smaller spark plug threads for like for my 110. It also came with extra little needles for the end of the guage hose. The hose itself already has a little needle installed in the end, it looks like a valve stem. My question is, if I add an attachment onto the end of the hose do I need to add an additional valve stem in it? Or is the one coming off the end of the hose itself enough? Basically if I add an attachment with a valve stem in it, the compression would pass through 2 valve stems.

Or did my kit just come with extra valve stems as a precaution?

[kilabeez0]

another question I have is how do you check compression on a motor that is out of the trike? I know your supposed to have the throttle wide open other wise it'll only read half the actual compression. Correct me if I'm wrong, but that's what I figured out after testing my other motors in the bikes. If I didn't have the throttle wide open it only read half.

But how do you check a motor that doesn't have a throttle cable installed? Just double whatever you get????

[Kevo225dx]

If you don't install the valve in the end of the hose, you readings will be low. The added volume of the hose doesn't seem like it would matter, but, it does.

As far as holding the throttle open; I have never noticed a big difference with it open or closed.

[bigreddaddy]

You can probably just take the carb off and check it.

[bigreddaddy]

By the way, when I first checked compression on my 250es I did it without holding the throttle open and it read 90psi. Checked it again with the throttle wide open and got 156psi.

[TrailerRider]

Why does holding the throttle wide open make a difference?

[NOS_350X]

It lets air into the cyl for it to pump it into the checker. No air no reading.

If you cant figure out any to open a carb to let the air in just take it off its only a hose clap or 2 nuts.

[kilabeez0]

so taking the carb off and testing it will provide accurate results?

how about if a motor is jammed in a gear? any way to test that? the motor that was supposedly the stock motor is jammed in a gear and wont go to neutral.

[Erics350x]

It should still crank over fine in gear with the engine out