80ci evo sputters at 4000rpm

I have a 80ci evo with a set of vance and hines pipes they are the long staggered pipes with 1-3/4in head pipes and 2in mufflers with a K&N filter my plugs look perfect when i pull them just a slight rust color after about 15k miles but for some reason i am having problems at 4k rpm it pops and backfires is this something i can fix by rejetting the main jet? at low rpms and mid throttle it seems fine just at 4k and heavy throttle and it hasnt always done this it use to run fine all the way past 4k so is there something i should look at or needs adjusting? any help would be appreciated... Thanks, Ray

Bag,

If what ur sayin is it was runnin fine before the pipes and filter and ur havn probs after the changes and at WOT then u probly want to bumb up the main jet. Iv heard that some evos came with jets as low as 160 so you prolly want to try a 170 and see how it goes. Ifn you are haveing probs at closed throttle then you want to bumb up the idle jet.

Ifn you had a cam like a EV27 then I know you would want a 45 or 46 idle jet and a 190 or 195 main. I say this because my evo has pipes, Intake, SE heads, and EV27 cam and Im runing 46/190 and I may go to a 195 when the weather warms up.

I had the same problem, my ignition coil was going bad, replaced it with screaming eagle coil, and cleaned the fuel filter in the tank, solved the problem, u should check the ohms reading in your coil, my fuel filter was partially clogged...

ok great thank you...i thought that might be the case but wanted to get some advice before i started going crazy on the carb...thanks again

And while yer at it and and have the Air cleaner off grab a V-DUCTOR and slap it on - cheap HP, Acc. gain. Also well whole the money.

i will check that too... my bike did run great with this setup until recently...i went ahead and went from a 185 to a 180 main jet and still having the same trouble so maybe the coil is faulty...i have another coil i will try it next...thanks for the ideas her i appreciate the help