Honda 400EX

[Banshee 79]

Hey guys my friend has a 2002 400EX, he has a FMF Powercore 4 Exhaust on it, with a K&N Air Filter and holes drilled in the lid. When he lets off the gas it backfires. I was wondering what main jets & pilot jets you guys were running for a similar setup. He is 800ft.above sea level, the bike is very hard to start in cold weather also. Any help would be appreciated. Thanks

[LightningEX]

I am running a Dynojet 170 main and a Dynojet needle on groove 3 from the top.My 400ex also is hard to start when cold.Tell him to try the 42 pilot jet from Keihin.I heard it cures this common problem and helps the fuel flow as well when you have a couple bolt ons.It costs like $4.99 from Dennis Kirk and the dynojet kit was around $60 I think and it came with a variety of jets.I have the 42 pilot ready to install on mine,just gotta put it in so if he hasent decided to get it or not in a week or 2 I'll let you know how it works.Hope this helps.

[LightningEX]

Forgot to mension mines also a 02 400ex with a DG complete exhaust system,K&N filter,and UNI filtered vents in the airbox lid.

[Banshee 79]

thanks for the reply he has a dynojet kit in it now, but he wants to go back to Honda main jets.

[DaleJrFan]

If it is real dry due to weather, you will run a little lean, you may want to check the packing in your pipe too. Here in Oklahoma, the winter has been pretty mild this year so I have gotten away with running the settings im my signiture, but in the summer, I know its time to re-pack the pipe when it starts to backfire a little, thats why I like my LRD so much, it's a good tattle tale.