## Checking for Compression

How do I check for air leaks and make sure I have good compression if I can't even get it to start?

thanks!

## Re: Checking for Compression

I usually pull in the clutch bring my piston to full exhaust stroke and pedal forward (while clutched) feeling the pressure on the metal and an ear around the cylinder. Compression gague is the correct way of doing this. I'm just a broke ass backwoodsman. not saying this is the RIGHT way just A way.

## Re: Checking for Compression

I put my thumb on the plug hole. If you can't hold the pressure back by pressing your thumb down as hard as you can then it should have enough to run.

## Re: Checking for Compression

Aaron i'm taking my right as an American citizen to disagree. Just because it pressed your thumb off doesn't mean it can hold compression. could be pissing around the ring or gasket. Thats just an initial shock, that means nothing for holding any sort of compression. Granted you will always have leaks around the piston and such. I used to do that untill my lawnmower had a cracked jug and still Seemed to have compression. Once again N00bies 2 cents. To each their own though.

## Re: Checking for Compression

Y'all are arguing about what the best way to do something wrong is?

## Re: Checking for Compression

Piss in a cup and drink it. Point Proven.

## Re: Checking for Compression

Make sure to NOT use one with a rubber extension... it'll drive you crazy!

^^^ fact

## Re: Checking for Compression

OK, so I've been wondering: is there a way to factor in the rubber hose part of the gauge? Can you calculate how much it will reduce your reading by based on the volume of the hose? I'm bad at math, but it seems like this should be doable with some number-crunching, right?

## Re: Checking for Compression

figure out your corrected compression ratio(after the exhaust port is closed), make sure to add the tube's volume to the combustion chamber's.

Then do the math. For example if you came out with 5:1CCR the math would be 5 to the power of 1.4, multiplied by whatever atmospheric pressure you have, sea level is 14.7psi. With a little oil in the cylinder to help seal your rings the gauge should show the same number your math came out with.

## Re: Checking for Compression

I cut a 1/4" extension off so I could chuck it in a cordless drill so I could spin the motor to feel the compression.

This is also a wonderful way to start the bike when your tuning it and don't want to pedal around like a madman while trying to set points, jetting the carb...etc.

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