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View Full Version : 300ex mild mods backfiring bad


Shartek
10-03-2009, 08:05 PM
i have an 2001 300ex.... i just went through the motor... piston .20 oversized.... I have a k&N air filter with open air box.... full DG exhaust.... stage 2 dyno jet kit... stage 1 hotcam..... my alltitude is 1,500 feet.... fuel screw is 3 turns out

idles great...... if i rev it to 2-3k RPM in neutral then punch it..... she spits then shoots a 6 inch flame out the back and then revs to redline.

backfires alot...... stock pilot jet...... its seems than when the main jet opens .... am i getting to much fuel or not enough....

I havent had a chance to put a load on the engine yet but if i give it a little gas in nuetral and hammer it......she bogges and dies....

any ideas
dirtdawg
10-03-2009, 09:09 PM
get a 40 pilot and a way larger main. my 250 did that and it ended up being 2 or 3 sizes bigger to be jetted right.
m0t0xk1d
10-03-2009, 09:16 PM
when putting the exhuast back on did you put the copper o ring in.

when i bought mine it backfired bad and when i took it apart the previous owner had permatex for the o ring. it didnt work. put the copper o ring in there and doesnt backfire at all
Shartek
10-03-2009, 09:35 PM
where can i buy jets from?




I was thinking of running a 400ex carb.... should i do that? where do i start with jetting on a 400ex carb
dirtdawg
10-04-2009, 08:09 AM
you can get individual jets from jetsrus.com.
roadthrills
10-16-2009, 09:52 AM
Check your timing. Sounds like you got your cam 1 tooth off.
laeger400
11-01-2009, 07:30 AM
Originally posted by roadthrills
Check your timing. Sounds like you got your cam 1 tooth off.

x2 very easy to do. make sure when you time it you roll it over by hand 2 times and the marks line up. and that the timing chain tensioner isnt stuck out. if it is and you put back to gether you will stretch the chain first time out.