Backfiring at 3/4 to full throttle

[trashedbanshee]

I just finished rebuilding the top end, have a pro design coolhead with 20cc domes, I have removed all the roughness from casting in the intake and exhaust ports, v force 2 reeds, fmf fatty exhaust, stock 26mm carbs with 270 main jets, k&n filter and no air box lid. Im riding in south jersey at about sea level and it was near 50 degrees yesterday. I have loss of power from 3/4 to full throttle. My low end is pretty responsive, mid range could be a bit better and top end it just dies and backfires.

 

Before the top end was rebuilt i had a stock head, fmf reeds, and stock intake and exhaust ports running 260 main jets and it ran good. I bought a dyon jet kit it comes with new needle jets, 270, 280, and 340 main jets. I also have a set of keihin 34mm pjs.....i took them off awhile ago b/c i couldnt get my quad to run right with them and went back to stock carbs. So anyway any help, tips or suggestion to get it running to full potential would be great. thankyou

[chevy7398]

your way lean on top with those mods and 50 deg out, need to be probally at least a 300 main with those mods and maybe a 310 with it being that cold

[akita8]

Make sure you have the choke crossover tube between the carbs.

[trashedbanshee]

The choke crossover tube is on, I'll even double check. If I change the main jets to a 300 or 310, would you suggest I change anything else? Should I change my needles to the ones that came with the jet kit I bought and what position should I put the clip in. Should I adjust the pilots? I really think that its starving for gas on top end, I just wasnt sure how much bigger of a jet I should use and if anything else was going to have to be changed.

[chevy7398]

when steeing your jettingyou have to startat the top and work your way down, (mains then needles, then pilots and air screws) as everything above will affect everything below, so get a 300 or 310 in your main and ride it, if its runs great from 3/4 to full then your main is good but do a plugchop to check, then go to your midrange, that is adusted byyour needles, then go adjust your pilots, with your mods i would bet that a 300 main, stock needles with the clip in the center slot, and the stock pilots with the air screws about 2.5 turns out would be damn close if not perfect.