ive been trying differnt jetting combos,the one problem i havent been able to solve is after making a long full throttle pass,say 1/4 mile,and then dumping off the throttle,i get a long steam of backfires out the pipe,if you hit the gas there is nothing,acts like its out of gas,putting the choke on doesnt seem to help either.if you just wait 5-10 seconds then hit it itll run fine.im running the dynojet kit with no lid,146/148 main jet,clip in #3 and 25 pilot,i have went up to a 27.5 pilot didnt seem to help,just rich at idle,also went up to a 148/150 main seemed rich,also have moved needle up and down doesnt seem to help,pulls through entire rpm range best with currrent jeting.i have been told the yz426 can have the same problem,what i was told is when you dump the throttle that back preasure from the motor blows the gas back through the carb?some guy in town builds a boost bottle type a deal to cure thison the 426,anyone got any ideas? my elevation is 3500ft

 

You are lean. I'm running a Ctpipe,open airbox, and a foam filter. Nothing else is done to my quad. I have the stock pilot jets in and my air screws are set at 1 3/4 and the other is 2 1/4. The needles are set at the third notch. Main jets are 170 and 175. I would say I'm at 3000 Ft.

 

Just my suggestion. Put the needles on clip #4 and open the air/fuel mixture screw 3 turns on each and your backfiring upon dump of throttle should dissapear. jmo

 

im running the dynojet jet kit thats why the jet # is small,also ive tried it with DJ148/150 mains and the needle in #4 clip and a 27.5 pilot jet, still does it and doesnt pull as hard because its too rich,also ive adjusted the fuel screws,with the 27.5 pilot to the point it was way rich at idle and it still does it

 

Derbyking,

I'd say dump the dynojet kit and get the round Mikuni jets with stock pilots, needles and airscrews. 170/175 Run that with air screws out 2 3/4 turns no lid. Pulls great at 3500 feet. Thats my set up and I've never had aproblem backfiring.

 

Make sure they are small round mikuni jets.

 

you are bottom end lean, make sure your air/fuel screws are a 3 out, and the same on both sides, also check for air leaks in the boots or header pipe

 

i think i found it.the head pipe from the left side doesnt make a good fit into the other,i swelled the end when i installed it and used high temp sealer,but t looks like it blew out,couldnt find anyone in town with a pipe exapander small enough so i heated the end and drove a socket in to swell it deeper.made a reall tight fit,havent got to try it yet but thats probably what it was,

 

Check the floats. You may be running it dry on your long wide open runs? Just a thought.

 

what's up? does mikuni not carry 175 or 185 jet sizes? my mechanic and the polaris/yamaha dealer here both say that they can't get those sizes. so i ordered a 170 to go with my 180. not really what i wanted to do. lashraptor, what's your take on this? i noticed your description listed what i need. where did yours come from?