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Hey guys looking for some help new to this forum thing so I have a 05crf250r with a 42 pilot jet and 175 main I'm having lean condition issues the header pipe will glow red and I will have backfiring when I turn the throttle back both jets are brand new and carb has been cleaned out fresh gas the bike has a fmf header and pipe and I jetted the bike to fmf specs as per their website there also is irractic idle can't figure this . out thanks for the help chris

What is your elevation ??

And are these conditions present while riding ? , or when on the stand ??

Have you checked the valves to make sure they are not getting tight and that may be the backfire ??

The header will glow red if the bike is idled for more than 1 minute

I'm at sea level or maybe a couple feet above

200ft to be exact

Have you tried adjusting the fuel screw , and if so , what setting are you at ?? (turns out)

I was 1 1/2 turn out and then moved to 2 and eventually 2 1/2 problem still stayed the same

Go up 1 on pilot , to a #45 , that should get rid of the lean condition on the bottom end , and get you back to 1 1/2 but without the popping

BUT

Make Sure your intake valves are not tight , they can give some of the same symptoms , you did not mention if you checked them when i asked

Also make sure the header to head connection is tight/sealed properly , as well as the mid pipe connection , any exhaust leak can cause it to suck air and backfire/pop thru muffler , acting like lean jetting

Honestly did not think it was jetting Someone before me had a 52 pilot in there didn't know why bike was the same way with the 52 I am gonna check the intake valve tomorrow I will let you know how I make out thanks for the help

Yea its sounding more like valves than jetting to me

So I checked the valves today l/s intake was .04 r/s intake was .05 and both exhaust valves were .09

0.004 is a bit tight , it might be giving some of your symptoms , it should be 0.006 +/- 0.001 , so 0.005 would be the limit you want to be at , not 0.004

You might want to check what shim sizes are in there and go 1 size thinner on the R and 2 on the L , if the size in there is anywhere near 1.20 , then you are at the shim size limit and cant go thinner , and will have to replace the intake valves to get it back in spec