Sound like fueling ..check the fuel tap it could be blocked or not turning on correctly, you could blow back through the tap with an air line
..I've seen this on motor bikes ....make sure the new fuel filter is not restricting fuel flow cheap ones are crap ..
don't forget about the spark plug ..I've had dogy ones out of the box on several occasions

 

You said you tried his carb on your quad, but did you try it the other way around, your carb on his machine? If his will run fine with your carb that really narrows it down. And if it does, I have to go along with CED and suspect your reeds.

 

I have taken my whole carb off lines hoses everything that attaches to the carb and swapped it with my friends carb and all his hoses. I put mine on his, and his quad ran fine, I put his working carb that ran fine on his on my quad and mine still did this. It runs about 15 - 20 feet wide open then sputters, boggs out, and then will eventually die, if I throw it in neutral it will run fine, also if I flip the choke it will get me by for about another 10 feet then if I keep it in gear it will die, but if I put it in neutral it will continue to run. Is it possible I have a partial plug in my exhaust that may only be effected when I get on it wide open, but will allow air to flow freely when I am not wide open??? I am just really reaching for ideas at this point.
Thanks

 

I can see why you asked for help! Since your friend is obvious a god one to let you borrow his carb, how about borrowing his pipe and muffler as well? They aren't that hard to take on and off. Also, when it dies have you tried immediately afterwards to turn the engine over, in gear, maybe with the pull starter, to make sure your drivetrain isn't binding. That seems unlikely but at this point you might be willing to try anything.

 

I don't think it's an exhaust problem. If it was restricted it would lack power but it wouldn't kill the engine.

 

I have seen mud get in the exhaust outlet hole and cause this same problem run a screw driver up in it and make sure it is open

 

Since it's a fresh rebuild, double check the torque of the cylinder base nuts. A couple of them are kinda tough to get at, but snug them up since it's been heated up. Also do like CED said, check your reeds, and check the condition of your carb boot....sometimes they can get a crack/tear in them.


Ken

 

I have a95 Xplorer 400 2- stroke and had the same type of problem and there was 3 items i found:1. muffler section had blockage, 2. Trash in main fuel valve ( where to turn your gas on and off), 3. The throttle and chock cable was not properly set. The chock adjustment on the carb body was the main problem, it's was not bottoming out when the chock was off. the bike ran great until you opened it up. Hope this helps.. it's what i ran into.
hunt

 

I have the same problem with my 2001 sp500 H.O.
Mine is in the shop they checked everything that you did and no luck. I am going to call him and tell him to check the exhaust and the tank valve also air in the fuel line. I sure inderstand the frustration I just want my Wheeler to work again.
Please keep us posted to what you find.
Thanks Shedhead

 

backfiring sounds like ign, weak spark. i am sure you have been told to check vent in cap or something restricting fuel flow in tank. also seen vibration from loose mounts on big bore bikes do same thing