compression problems

i have a tomos bullet w/ a a-3 engine on it w/ compression problems. it is reading 90 maximum pressure. so i replace the piston, cylinder, and rings. unfortunately im still only reading 90 on compression. is there any were else i may be losing pressure that i may have not checked? any help will be appreciated.

Re: compression problems

Don Pflueger /

there's only a few places compression can be lost.


head and cylinder mating surfaces

cylinder to engine case mating surfaces

crank seals


loose spark plug

lack of or missing exhaust exhaust

Re: compression problems

Steamboat Aka J. R. Stevens /

Hey Donp, as you pointed out, the compression may increase after break in of the new rings and cylinder. Jim

Re: compression problems

Don Pflueger /

yep, it might. 90 is a little too low tho. does it run? if so, i wonder if the guage is bad?

Re: compression problems

Don Pflueger /

i dont know why i didnt think of this before. must be slipping in my old age.

do you have the throttle held wide open when checking compression?

not opening the throttle limits the amount of air drawn into the cylinder and will give you much lower readings.

also, if its still low with wide open throttle. take the bike to a lawn mower shop or automotive shop and ask them if they can do a leak down test. this will tell you exactly where your compression is going.

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