I was at Little Sahara last weekend and I was coming down sand mountain (a very tall hill). Anyway when I was coming down and not giving it gas it would back fire. It also does this sometimes when I'm hauling *** and let off the throttle. I run a 155 main (5000 ft. plus elevation) w/ WB's slip on, K&N and no lid. I've checked the plug and it looks good. Could it be the pilot?? And if so, any suggestions on size?? Also can you get to the pilot w/o taking off the carb? Just from the bottom of the bowl like the main?? Thanks, Drew

 

BackFires indicate that unburnt/unspent gases are exploding in your head pipe... Is your air/filter clean... Try it with the lid back on with some holes... You might be running to lean also I would bet that... With the airbox lid off you are flowing more air. I run a 165 with airbox lid off.. Kick up that main jet to a 160..

 

Backfiring is a sure fire indication of a lean situation or maybe an exhaust leak.

 

I agree w/ supra - check for an exhaust leak.

 

Like I said it rarely backfires, maybe every 3-4 rides. I have checked the exaust and it's fine, atleast where the slip on meets the header pipe.

Also, Skunky, when I put on the air box I lose alot of power and it really sputters. I'll try going up one size. Any more help is appreicated. Drew.

 

ya i figured that about the air box... up your jet size..

 

Mine does the same thing, just an occasional small backfire while decelerating/engine braking. I've got the WB E-series as well, but I run with my air box lid on, and I'm also running the 155 main (anywhere between 1000ft and 3000ft elevation). Since it's at zero throttle that the backfiring happens, I think it would have more to do with the pilot jet being lean than the main jet. I just haven't gotten ambitious enough to tear apart the carb to put a 40 pilot in. How hard is it to install the pilot? Do you just take the fuel-bowl off and it's right there?

 

Skunky...I know I'm probably beatin' a dead horse....but..sometimes I go to some dunes that are around 2,500 ft. elevation (St. George, figured you've heard of it)..however, I mostly ride at 5000+. Would I need to jet even higher than the 160(as you suggest) to go that much lower...like a 170 or so?? And where can one get a pilot jet?? Don't see them in any of the mags or catalogs. And Skunky..are the dunes near Vegas by Nellis?? Just wondering. Thanks, Drew.

 

you're right motorhead, the backfire on deceleration is caused from a lean condition in your idle circuit (pilot). You need to adjust it to make your idle mixture (fuel/air) richer by turning the screw out in 1/2 turn increments (max 4 complete turns out) If at 4 turns out it still does it then move up to the #40 jet. The mixture screw is located in front of the float bowl on the bottom. Look in the tech connection on the main page and select advanced search, you will find all your answers there - I did.

I'm really getting tired of reading some poster's propagation of misinformation on every post like this. Do the postee a service and get the information right before you diagnose a problem; when you lead them down the wrong path by "reading tea leaves" you may very well cause harm to their machine.

ogre

 

I am really gettting sick and tired of people getting sick and tired.. As vor the vegas dunes .. ya they are close... Just because you are reading the dynojet instructions for elevation does not mean that is what your machine wants..