My 400EX did have the White Brothers E-Series pipe with silencer.

I have recently purchased a Curtis Sparks X-6 pipe and silencer. (The silencer DOES NOT have a spark arrestor.)

I installed the pipe and silencer combo, and used anti-seize.

My carb is stock.

My carb is jetted for the White Brothers pipe. The main jet is 151, and the pilot is stock.

After allowing the motor time to warm up, I decided to see what it sounded like. I reved the motor, (Not wide open.), and held it there for about 4 seconds.

When I let off the throttle, the motor started going back to the idleing stage. (Like it should.)

Just before it got back to idleing, it back fired!! A flame came out of the silencer.

I know that's not supposed to happen.

Can someone give an answer to what I need to do?

 

I would say to richen it up. Everyone has had somewhat different results with jet sizes depending on locations across the country. For grins I'd try a 160 but you may end up going to a 165. It's a game of trial and error. Even when mine was stock with just the MegaMax and K&N (stock head pipe)I ran a 158 w/lid.

 

With the pipe came a set of instruction on what the jetting should be for the Sparks pipe and they are very good about what sizes work. If you got the T-6 pipe you should have a 440 engine, because the T-4 is for the stock engine. A good ball park number is 45 piolet and 160 main with the clip in the middle. these are number to start with if you have a 440. Stock is 42 and 152 for the pipe.
You will find that the Sparks set-up is about the best that you can buy but it is loud and at night it will shoot flames out the end.

99 440ex(stolen but found)
2000 400ex for sale

 

Believe it or not, an instruction booklet was not shipped with the packing.

I will be calling Sparks Racing after the holidays are over with, to see what they recommend.

Until then I will play with the jetting.

A 2 stroke and a 4 stroke are two different worlds when it comes to set up.

Thanks for the help guys.

Merry Christmas!!!!!