Hello to all here. I've been hanging around here for awhile, and seen some pretty decent trouble shooters hang out here. Maybe you can help me with my issue. The quad is a 1987 TRX200SX. It was bought new by me in the Fall of 1986, ridden for like 5 or 6 years and stored until a year ago when I decided to rebuild it for my nephew. Neways, I've bored it out, re ringed it, new piston, new valves, valve job, new valve springs, new timing chain, clutch springs and discs...etc and everything went easy and right. Neways, everything was fine, it was running pretty good at that point.
This morning I rebuilt the carb (after it soaked in carb cleaner overnight, and blew it all out with compressed air) changed the plug, and changed the stock exhaust out for A Cobra "Performance" exhaust system. It started right up when I finished and runs really strong. (a heck of a lot better than it did before I started)
My problem is that it pops back through the muffler when I let off the gas from full throttle. I have checked the timing, checked the plug (it looks right), and played around with the carb air adjustments,
checked the valve lash settings, and changed the plug out. I suspected that maybe the exhaust was leaking so I also re torqued the exhaust connections. I also played around with the pilot jet on the carb, lean or rich it makes no difference, still pops. I'm running a 50/50 mix of Sunoco Race Gas and Premium gasoline, if that makes any difference. (I'm more of a car guy, specifically Dirt Track Racing Cars) This quad runs a lot better than when I started, now if I could get rid of the pops. Thanks for any insight you can provide.

 

Was there a crush gasket on the manifold? Might try putting a new one on. Do the pops diminish with the choke on once it is warm? Popping on decel, especially throttle off is a lean condition somewhere I would think.

 

Yup...I replaced the Copper crush gasket with a new one.
Hmmm...I don't know about the choke on when warm.
I haven't used the choke to start it even, because it starts right up without it.
That would make it run richer, which would tell me if it's too lean. That's a good idea.
Yeah....that's the way it is with cars as well...I thought it was lean as well,
but I went down a notch on the pilot jet, and it did nothing maybe I need a bigger main jet
due to the bore and new exhaust. Do it in NY!
Thanks for your input.

 

Maybe you just didn't write what you meant, but try going up on the pilot. If you went down in size from where it was stock, then that is almost certainly your problem.