Backfiring with new pipe Jetting Help!!!

[04'400ex'er]

I just put on my hmf pipe and rejetted the carb. I had previously put in a 155 main when I had added a K&N filter, removed the air box lid, and removed the spark arrestor. Now with the pipe I installed a 160 main jet. HMF told me I needed a 152 but that was with the stock filter and lid on. Then they told me to set the air fuel screw to 2.5 turns out. Now the bike is revving great, but backfiring when it decelerates. It is blowing a big flame out the tail pipe. Am I lean or Rich, And what do I need to change? Please help with the jetting problem because I am fairly new to this. Thanks in advance

[04'400ex'er]

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[cals400ex]

you need a larger pilot jet and/or to turn the fuel screw out more.

[04'400ex'er]

Originally posted by cals400ex
you need a larger pilot jet and/or to turn the fuel screw out more. Thanks alot man. Im getting a larger pilot tomorrow.

[kilabeez0]

wouldn't he need a bigger main?

[nosliw]

Originally posted by kilabeez0
wouldn't he need a bigger main?

if he was popping/backfiring at 3/4 to wide open throttle then yes.

http://www.atvriders.com/articles/jetting.html

[kilabeez0]

haha, that's exactly what i was going to post!:devil: i had to print that up, i always forget what does what:macho

[cals400ex]

since it is backfiring when he lets off the gas, he needs to change his slow circuit (pilot jet/fuel screw position). most recommend a 42 pilot jet or so. by the way, it is a 21 series keihin pilot jet if the shop asks what model it is.


i ran a keihin 158 with the same mods as you. however, temperature and elevation play a pretty large role.