G1 compression testing, correct way?

[dwmmatt23]

Ok Ive searched and found mixed results, what is the correct way to compression test a G1 motor? My cart will not start, just spins but will not fire and first thing I did was screw in compression tester and crank over motor, read @70#. Some say doing this on a cold motor and not having carb tied wide open will get a negative read? Trying to make sure before I tear into motor. I already jumped ahead of myself and removed motor but will only take 10min to put it back in if I need to re-test

[Field6565]

A reading of 120psi is new. Except 82 motors. They had somewhere around 90 psi. With a reading of 70psi? Thats not even close..... I don't think it matters how you checked it. That's low. By the way nice cart. Any more pictures to share?

[dwmmatt23]

Others have said this way would give a false reading, so the way i did it is correct? Also if i pull the fuel line off the carb from the fuel pump it pumps out alot of gas, ive read with low compression it doesnt have enough to pump the gas?

and heres the link to my sig pic build with more pics
http://www.buggiesgonewild.com/membe...uild-pics.html

[slonomo]

So is this for a G1 motor or for your sled motor? I'm confused....

Anyway, I have had alot of trouble with compression testers. I've tried 3 different brands from 3 different sources. NONE of them tested higher than 60 psi....? My cart starts right up and purrs like a kitten and goes 26 mph. So I guess the gauges aren't right....? BTW I used the warm engine, oil in cylinder, WOT procedure.

If it's your G1 engine, I'd check spark also. If it looks good then you might want to pull the jug and check it out. You'll prob find a broken ring.

[dwmmatt23]

This is for a g1 motor in a new project

[slonomo]

Yeah you've got it right, warm engine, a little oil in the cyl, WOT. As long as your gauge is better than mine you should get an accurate reading.

[technoid]

Originally Posted by dwmmatt23

Ok Ive searched and found mixed results, what is the correct way to compression test a G1 motor? My cart will not start, just spins but will not fire and first thing I did was screw in compression tester and crank over motor, read @70#. Some say doing this on a cold motor and not having carb tied wide open will get a negative read? Trying to make sure before I tear into motor. I already jumped ahead of myself and removed motor but will only take 10min to put it back in if I need to re-test

The best method is the Aircraft mechanics way. Its called a leak down test. You apply air pressure into the cylinder with the piston held at TDC compression stroke. The leak detection of lost air lets you know where your loss is. Valves or rings. Leak down testers are a set of gauges. One tells you supply pressure and the other says loss. More than 10 psi loss is bad.