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Discussion Starter · #1 ·
Hello I have a Chinese kazuma 50cc quad that I am only getting about 40 psi compression.
I have new cylinder head assembly( with new valves, rocker arms and valve springs), new piston with rings (seems like a tight correct fit) and timing appears correct. Usually that would fix the compression issues.
Any ideas on what to try next?
Tried putting a little oil in the cylinder and still no change.
thanks
 

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Well if the oil made no difference, then the rings are presumably ok, so... the valves are leaking/not closing. If you had compressed air you could introduce some into the sparkplug and listen for air escaping out the inlet or exhaust.

Generally, even with badly worn rings, the oil will raise the compression quite a bit(as I'm sure you know). So.. it would seem to be the valves. Did you lap them in ? And check they were sealing by putting a bit of petrol in the combustion chamber with the head upside down ? Are you sure about the clearance, and are you sure about the cam timing ? If you could slip the cam chain off, close both valves, then turn the crank by hand, you should get compression.
 

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Discussion Starter · #3 ·
Thank you for the help I appreciate it. I’m going to do another leak down test. I’m thinking that the intake valve could be sticking open occasionally.
 
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