[Jacob Braun]

I have a 400ex that's backfiring on deceleration. Initially i thought it might be running lean but then I noticed it blowing a bit of black smoke on full throttle. This made me think it's rich. The backfiring isn't very bad but its definitely noticable. I also noticed it bogging a little in second on low throttle. I looked at the jetting and it's running a 165 main, I didn't check the pilot. It also seems to bog down/stutter at full throttle. I'm running no airbox lid, stock air filter and a yoshimura exhaust (the exhaust pipe is cut down shorter, old owner). Not sure if the header pipe is stock or not. Anybody know if it sounds to be lean or rich?

 

[Eric the red]

I think its both.
Sounds rich on the main and lean on the pilot.
Check the exhaust for tiny leaks, a leak will cause back firing.

 

[Jacob Braun]

I think its both.
Sounds rich on the main and lean on the pilot.
Check the exhaust for tiny leaks, a leak will cause back firing.

That's what i was thinking, though I didn't know it was possible. I know there is a leak where exhaust slips on to the header pipe. Would that cause the backfiring? And what jetting would you recommend? Something like a 160 main and 42 pilot?

 

[Eric the red]

160 main with 42 pilot should be close.
The leak at the header pipe will cause the back firing.

 

[Jacob Braun]

160 main with 42 pilot should be close.
The leak at the header pipe will cause the back firing.

Ok, thanks. Do you know a good place to order a jet kit? Or would it be better to get it from a honda dealer?

 

[Eric the red]

Call the dealer, they might have them.
Years ago, the dealers had a tray full of jets with most every size but now they order every little thing they need one at a time.

 

[oldskool83]

JETSRUS.com dealers have no clue how to jet anymore, or have the stuff is stock. Its lean, its cant be lean and rich at same time. EVERY 400ex should be be running a 42 pilot at min! even if stock. Mains depend on air filters and exhausts...blow in a 180 and start from there, if it feels like crap riding than is flooding it. Back down 10, go up 5 back down 2....only way to get it done.

I can jet anyones bike. It takes hours however if you have no clue what your doing.

 

[Eric the red]

It would take a few hours for sure if you start with a 180 main in a stockish 400ex lol.
Years ago, the go to jetting for a slip on pipe and no air box lid on a 400ex was a 40 pilot, stock needle and 155 main. If you kept the air box lid on it a 152 main was big enough.

One dealer near me has jets, he sells and races two stroke bikes and everyone and there dog swaps jets in those.