My KLX 300r backfires when I come off the throttle at higher speeds. I have the buttplug out and the crank case reroute with K&N air filter and uni filter, is my bike running lean and causing the backfire? Can I cure this by backing out the pilot screw in the carb a bit?? Thanks!

 

A guy down in Florida experienced this on his KLX250S after installing his HMF exhaust. I thought that his bike was breathing so much better than he had created a lean condition. As it turned out, for some reason he was running rich. I am not sure if he ended up swapping out his main jet or what, but it was definitely a rich condition.

I remember it only because it seemed completely opposite from what I been taught to expect.

It was pretty cool, though, because he was actually shooting a 6-12 inch flame out of his pipe each time it happened.

Now that I think of it, I think folks ended up deciding that the condition probably exhisted before he swapped the pipe, but the catalytic converter was dampening out the backfire. Don't know if this is true or not, but I remember folks saying that.

Don't know if this rambling helps at all, but this is the only other KLX250S that I have actually witnessed backfiring so I thought I would share it.

 

My bike does the same thing. I have a Muzzy exhaust, UNI filter and all other basic mods to the airbox and smog junk. I might be running a little rich. I believe I have a 130 or 132 main in there. I tried the 128 and it made less power and felt like it was lean surging a little. I might try leaning the pilot screw a little. I think overall it's a result of the slide hanging a little from drilling it out. I don;t think it will hurt anything, and not a loud backfire, just some light popping. I still have hte spark arrestor and quiet core installed, so I don't expect any flames shooting out.

 

If you think your slide is "hanging a little from drilling it out", then you probably did something wrong. The hole does not come in contact with anything ... it simply lets air flow through it quicker. The hole on the right is the one to drill:

 

Have you done any carb re-jetting Whiteman?

 

No I haven't rejtted, would I be wise to get a jet kit? I have read that this may fix the problem, do you think it would?.... but also was wondering if I could back out the pilot screw on the carb to solve it?

 

With the "Free Mods" you have done you must re jet. With the stock carb, I would go with a dynojet kit. They are about $50.00 to $60.00 I think.A little pop on decel is normal and OK. If you are popping a lot, I would plug it back up until you get the jet kit.

 

Well am I too rich? if that is the case I guess I would be turning in the pilot screw!

 

Just read Agoos msg now: Next time I ride I'll see how bad the pop actually is, I just got the bike (02) and had it popping the first ride, (not used to that nice bike sound either) I will go with the jet kit if needed, I have never jetted a carb myself before is it difficult?

 

The stock CVK is really easy to work on.The instructions with the Dynojet kit pretty much guide you in the right direction as to what jets and clip position to use. The good thing about the CVK is once jetted properly it is good for a wide range of elevation. The bad thing about the CVK is it does not have the throttle response of a pumper carb which is much nicer for off road riding. If you do a search you will find a bunch of info on the Dynojet kit and about pumper carbs.