backfiring?

[JR_rivard]

i just put a hmf full system pipe on my 400ex, adjusted valves, re-jetted to a kelin 160, changed oil, and put in a new plug. i started in up this morning to get it in the back of my truck and it backfired several times and smoked. does this mean my jetting is off or do i need to warm it up a little more? just dont want to mess anything up.

[miller821]

Sounds like your jetting is off.

[cals400ex]

make sure you have no exhust leaks where the header meets the head and also where the header and silencer meet. also make sure your air boots are tight at every connection (where they meet the carb and the head). you may need to turn the fuel screw out a 1/2 a turn or so as well.


there is a good chance a higher quality oil will not burn as easy as some of the cheaper brands..

[Wheelie]

Install a #40 pilot jet, and try a 155 or 158 main jet.

[krt400ex]

Originally posted by Wheelie
Install a #40 pilot jet, and try a 155 or 158 main jet.

My stock 400EX came out of the dealer with a 158 mainjet. Going to a 155 is way to lean. Did you remove the airbox lid? If you did I'd say go to at least a 165 main. If it's backfiring it's too lean. The smoking could be because you're not running the right oil or you didn't adjust the vales properly. I run Belray Thumper oil. It's a semi-sinthetic blend and it's viscosity is 20w-50. My bike runs great on that. Also, sometimes mine smokes a little when it's cold. Thats no big deal. The same thing used to happen to my 300EX. Your choke may not be opening up completely when you turn it off causing to much gas and not enough air getting to the engine, which would make it smoke.

[Sleeper]

"My stock 400EX came out of the dealer with a 158 mainjet"

It should'nt have.. They come stock with a 148 main.

Just for info. My WB E2 came with a 155 main to install (for stock intake).


Sleeper

[JR_rivard]

there is a little leak in my exhuast where it connects, what is the best way to fix that? i pulled the plug and it was pretty white, so im gonna move up a few jetting sizes, and turning the fuel screw out makes it richer right.

[Halter]

mine used to backfire alittle bit with me E-series white bros but with a 160 size jet but then I put this R4 White bros on it and now runs like a raped ape...

its just key to get all your jetting and make sure everythings in the right place..then you will love the result!!

[fatkid400]

Originally posted by JR_rivard
there is a little leak in my exhuast where it connects, what is the best way to fix that? i pulled the plug and it was pretty white, so im gonna move up a few jetting sizes, and turning the fuel screw out makes it richer right.

Replace the exhaust seal.for a 2000 that seal is prolly shot.
Anyway just checkin to see how your liking the pipe?I guess when you get it jetted you'll let me know:D

[bmurray]

148 is the stock jet, not 158.