jetting with pipe

[Nate_450R]

i put on a trinity stage IV exhaust on my 450R and over time it has developed a rapid backfire when i let off the gas and the bike idles down. i was curious if anyone else has had this problem or possibly the temperature has messed up the jetting. it was early january when it was put on so it has warmed up alot since. all i have done that would mess with jetting is that exhaust and a k&n filter w/ outerwear. right now i am somewhere between a 172-175 main jet and the stock pilot stock clip position with the stock needle. any suggestions on where to go from here? any help would be great.

[trx250r180]

try 50 pilot,2 1/2 - 3 turns out micture screw 180-185 on main,4th to 5th clip on needle

[400exrider707]

Originally posted by trx250r180
try 50 pilot,2 1/2 - 3 turns out micture screw 180-185 on main,4th to 5th clip on needle

I would do exactly this, except keep the main you have now.

[Nate_450R]

thanks alot guys, ill be picking up the new ones and putting them in wed. hopefully this will fix the problem.

[Nate_450R]

so that didnt work at all. 50 pilot, 180 main and it wouldnt even start. its a kicker so it wouldnt even try to start. right now im at a 45 pilot and 172 main while i wait for a jet kit to come in. im hoping a 45 or 50 pilot with a 175 main will work. but i dont know. what is stock on the 450's? is it possible i am just extremely rich? i have no more thoughts on this, my brain is racked. i seriously need help with this one. thanks guys.

Nate

[trx250r180]

did it still start with jets you ran for a while? may need to start there ,get running and try bumping pilot 1 size ,stock is 48,if still has problems your valves may be too tight if wont start cold

[Nate_450R]

ok so you think a 48-50 will work? then maybe a 175? it starts but still has the backfire with the 172 and the 178 but with the 180 it wont start. i dont have the 175 yet because they were sold out so im waiting on the kit to get here from Nashville.

i dont know my way around the motor on this thing that well...how do i go about messing with the valves? is it something i should do or have someone else do?

[wilkin250r]

You need to understand a little about how the carburetor works. The carb doesn't magically know what RPM you're running, or what gear you are in, or what size tires you have, or anything other silly thing. The only thing it knows is THROTTLE POSITION.

If you are at basically zero throttle, the carburetor is working in the pilot jet and air screw. Most often this happens at idle, but it can happen at other times. (like cruising at 45mph in 4th gear, and letting off the throttle. Even though you are still at 5000rpm, your carb is working on the pilot because your throttle is closed). So if you have backfiring when you decelerate, it usually means your pilot is lean.

Bumping your main jet to fix a starting problem, or idle problem, or decelerating problem WON'T FIX THE PROBLEM. Changing the main won't affect a pilot-jet problem. That's like changing your tires because your gas is leaking, it won't help.

It's possible you might have several problems. They need to be treated individually.

[Nate_450R]

wow, that clears alot up...i wasnt aware that the pilot and main controlled different things. so, ill start with the pilot and work from there. but thanks for clearing things up for me...i would have worked for hours and probably never have gotten it right.