WB exhaust backfire??

I put the WB Pro Meg exhaust with the head pipe on my 400ex and it started to backfire when I let off the gas anywhere after 3/4 throttle. So, I rejetted (bigger main jet) and messed with the discs and got most of it to go away, but it still backfires. Not as much as before, but still backfiring a bit on deceleration. I called WB and they said that the PRO Meg exhaust wasn't meant to be put on a 400ex without engine work (like mine!). They said in order to get it to run optimally I'll need some engine work(at least a cam job). What do you guys think? Have you ever heard of this type of problem with this exhaust? Any info would help.

[Deathbringer]

This is not personal advice.. but I have called and talked many times to WB and they seem to be on the up and up...so with that said.. If they say it is not meant for your bike without mod'n the motor and stuff, then I would take what they say and either return the pipe and get the right one (E-series works good) or mod the motor.
Good luck, but I think you are beating a dead horse...

[Wheelie]

Keep your full system, also keep the same number of discs the pipe came with on the system. This is where you will achieve optimum performance.

What main jet are you running?

Sounds like your slow/pilot circuit is too lean. Step the pilot jet up to a #40 and set your mixture screw out 2- 2 1/2 turns.

BTW--Did you change the gaskets that seal the headpipe to the head? Check the torque on the header pipe bolts, and check the system thoroughly for exhaust leaks. Exhaust leaks can cause backfire.

Good Luck!

[nakomis0]

Ya take wheelies advice. The pipe should work on non modded motors. I think the guy from WB was a newbie or something.

When this happened to me, I jump up the size of the pilot jet and it went away. I just recently did the 416 kit and XR cam, not I have the backfire 'back'. I'm gonna jump the pilot up a couple sizes and it will probably disappear. It's cheap to do and worth a try.