1985 trx125 rev help?

[ParaNormalAudio]

I have a 1985 trx125 engine on my buggy. Just got it in trade. Its never ran 100% right. At first I just thought its a carb problem easy fix. Ive cleaned and retuned the carb 3 time and nothing has gotten any better. Im worried I may need to rebuild it.

Motor runs great at idle. Starts no problem.
Will not run anymore than half throttle without choking out.
If I pull the gas all the way it chokes and if I dont let off it will stall.

Carrying a person even in first gear it wont get up to 1/4 throttle. Sometime it will make it to half then bog back down seconds later.

Not sure how else to describe my problem. If you think you can help please any questions you need to. Any help is appreciated. Thanks in advance.

[Here 2 help]

Check the compression (throttle held open) - should be about 120psi

If the compression is OK, the problem is probably; (a) carb (b) cam timing (c) spark timing.

If the compression is low (below 100) check the valve clearence and recheck the compression. If still low, do a cylinder leakdown test to find out where the compression is leaking out. If the cylinder leak down is OK - the problem is probably low valve lift caused by damaged cam and rocker arms.

[ParaNormalAudio]

Ok Ill be able to check compression later today. Ill post what I find out.

Im hoping there is no problem other than in the carb. It has a cheap replacement carb from ebay on it. ISO Performance I beleive. Maybe thats the problem.

Other than that and a uni airfilter the engine is stock. Never been opened for any reason so I could see with its age it needing a rebuild. New piston and some block honing im willing to do. most likeky anything other than that or valves
im just going to sell it as is.

[ParaNormalAudio]

Ok got it running "better" still not where it should be.never did get a chance to compression test it.

I took the air box tube off. Now it runs alot better. Took it up and down the street carry me and my brother just fine.


So I tried it with the tube in place just no lid. Still the same problem. I think my air filtet is just to thick. Its all foam but like 5-6" thick.easily 2" around the center. Im going to try a thinner filter tomortow.

[Here 2 help]

It's hard to troubleshoot blind - sounds like someone jammed a piece of foam into the airbox in place of the filter. If you are going to try "thinner foam", make sure it is open cell foam - better yet, get a real air filter designed for the application.