I have been riding my 250 now with the following mods:

Two Brothers pipe, Uni filter, jet kit and snorkel.

fuel screw was just over 1 turn and I went to 2.
main jet 128
needle on the 3rd notch from top
stock pilot jet
drilled slide to 7/64th

My exhaust is now turning my fender black. Does this come from running to rich? What should I be changing for this? Im also getting popping when i decel. I read that if it pops to put in a bigger pilot or back the fuel screw out. Both these wont help with the black fender and my theory that im running rich. After about 4k RPM the bike runs fine so the main jet should be alright? Under 4k RPM is where I think im getting the problemm it seems to have a lack of power here.

Any advice where I should start?

 

could still be lean under 4k. Check the color of the spark plug after running it under 4k for a little while. If it's white, too lean or you have an air leak. If it's black & sooty, too rich. Popping on decel usually means lean. The black on your fender could just be normal exhaust gasses.

 

Remove the airbox lid.

 

What he said. Report back with updated results.

 

what elevation are you? I went 2nd notch from top at 0-3000 feet with screw out 2.5 turns. same jet as you. I used the dynojet kit. Do you have the stock needle?

 

im riding pretty near sea level. Running the dynojet needle.

 

your definitely not running too rich. I used a the 132 main 2 - 2 1/2 turns out and it ran great. with K&N no lid or with kdx snorkel and at sea level. keep in mind temperature has a factor in fuel ratios. the hotter the richer, the cooler the leaner your gonna run my average temp were i ride is 60 to 65 Fahrenheit

 

I believe mine is also a 132, I sometimes will get slight popping when letting off quick on the throttle but i was told this is normal. It doesn't do it all the time only when letting off quickly after being hard in the throttle. Possible unburt fuel igniting as exiting thru the exhaust? Just a guess.
Rich is better than lean!

 

Your temp ratio is backwards. The hotter climate = leaner, colder climate = richer. Air density is the factor for temperature vs barometer (air pressure, elevation).

 

air density is relative to pressure but am I wrong in saying that the colder the air the more density it has. and warm air has less density. hence this is why people put cold air intakes on there vehicles to increase volumetric air flow(more air) which will lean(less fuel) your mixture out unless u adjust for it. Not trying to stir things up but if I'm wrong enlighten me please.

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