Check the compression and use a timing light to see if the plug is firing inside the combustion chamber - note: use a new spark plug for testing.
I will try this today. I was told that there are a lot of CDI's that are not as they should be, I ordered one from amazon that was said to fit this trx125 and it did fix the no-spark problem, but now my friend has me wondering if the CDI is an aftermarket that will not fire as it should, I do know that it is smaller than the CDI I originally had taken off. Could this also be the case?It's a weak spark - if the plug is new, try removing the resistor spark plug cap (it screws into the coil wire) and see how far the spark will jump from the wire to the engine - at least 1/4 inch in normal and if it will jump 1/2 inch it even better - some ignitions will jump a spark more than an inch. You might want to check the grounds too - between the engine and frame and coil to wiring harness or frame depending on it's mounting.
What should compression be on this? It is a 1987 Honda TRX125Check the compression and use a timing light to see if the plug is firing inside the combustion chamber - note: use a new spark plug for testing.
Ok, what would cause it to have only 35 psi? I really would like to fix this issue.Throttle wide open about 120 psi - throttle closed it might get to 120 with a few minutes of cranking, but throttle open should get there within about 5 or 10 strokes
How do I fix it if the valve is stuck open? It ran well when parked, but sat up for months.First suspect is the valves - valves lose clearance during normal operation and eventually get tight enough that when the engine cools a valve may be open. Generally the problem occurs gradually. The engine gets progressively harder to start when cold until it simply will not start. If it's not the valves and the engine spent long periods of time idling, then the cam and rocker arms might be worn out - worst case, the rings are worn out.
Also, can it be done without pulling the motor?How do I fix it if the valve is stuck open? It ran well when parked, but sat up for months.
Bad news all the way around - the engine has to be removed to remove the cylinder head and the cylinder head has to be removed to fix the valve - now the really bad news; the valves are no longer available from Honda and neither are gaskets to reassemble it. The gaskets may be available on the aftermarket, but the valves are another story.Also, can it be done without pulling the motor?