Okay, so my trx70 has needed to be rebuilt for some time. So I decided it was time to finally do it. So I ordered a rebuild kit which came with a new cylinder, piston, and ring. Everything went very smooth. The head looked great and the valves looked good, they seemed to seat well. Anyways, after getting everything together I start it up and let it idle to warm up, then I go to take off and when I put it into gear and tried to give it some gas it died.....so I started it back up and tried to rev it in neutral and it just started sputtering and backfiring a bit. Immediately I thought carburetion and tried changing the air/fuel mixture. It seems to run better leaner and by making it leaner I have been able to at least make it move. But it has no guts. When you pull the pull start you can feel the compression and the engine isn't making any noises at idle to about 1/4 throttle, but past that it sputters most of the time. I am stuck, I am thinking carburetion but am not sure...

EDIT: Oh, and if you slowly rev it up it will rev up, but never seems to reach full RPMs and does sputter a bit.
Oh! I should also mention before rebuilding it it did have a bit of an issue where if you just went 100% throttle all at once it would try to die.

 

Well, after cleaning the carb it now doesn't sputter anymore, however it still won't reach higher RPMs....I have tried different jet settings with no avail.

 

My WAG is you got your cam timing off. You can double check that and also do a compression test.

 

No, I checked the cam timing and I don't have a compression tester...Also, sometimes it idles beautifully and other times it sounds like it wants to die and does. Would the cam timing do that anyways? I would think that would be more ignition timing. If it was cam timing wouldn't it run a lot worse in the lower RPM range? Hmm, anyways, I guess I could try advancing the timing a tooth and maybe taking it back a tooth and see what happens. It is an old quad and maybe the timing chain is stretched a bit.

 

It depends if the cam timing is advanced or retarded. Because if you have the cam timing advanced it will have no top end at all. If you retard the cam timing you will have no bottom end. Technical Specs & Information


It could also be ign timing but everything I have worked on was fixed as long as the key was good.


Why play with carburation if it was running good before the rebuild?


Something was changed during the rebuild process. Problem is there are a lot of things that could go wrong during a rebuild. Just an example is: Were the rings put in correctly? If not, you're going to be way down on compression and that will cause problems and there is no way to determine this because you don't have the tools to check.


In any event good luck and let us know what you find out.

 

I put the rings in according to the manual and made sure the writing was up, I spread the gaps out and I even oiled them.