Proud owner of a 2002 BAJA, best machine I have been on yet! All stock except K&N filter, 22 inch rear Dirt Devil and 23 inch front Shredder. The problem I am having is when I ride it hard (meaning high thottle, quick on/off thottle etc....)and come down to an idle. Once I hit the thottle to take off again, "flame out" back-fires thru carb! Only does it when I really ride it, not putting around the yard. Starts right back up and does not miss a beat. No high end flutter or miss. Use regular gas. Will sit and idle for ever, does not load up. Valve clearance problem? Too lean or rich? Plugs look fine. No gas in oil. Choke works fine. No gas coming out overflows. Tank vent not plugged. Stock gas cap(not vented). No racing, just Pennsylvannia trial riding. Based on GPS unit, runs down flat blacktop all day at 76 MPH with my big 213 pound butt on its back. Frustrating problem, any ideas??????? Thanks

 

You might need to re-jet with the K&N or adjust the mixture screw a little.

 

use 91octane gas not regular!

 

If you just bought it used, then you really should check out the valve clearances. I bought mine used and the intake valves had zero clearance. To my surprise many people had the same problem with the intake valves from neglecting to do it for a while. It's a pain in the *** but someone's gotta do it, and now thats you.

 

Check out this link: http://www.mikuni.com/fs-tuning_guide.html

It says the problem should be a lean carb or intake valves. So definitely check them.

 

Thanks for the info. Checked valves tonite and discovered exhaust valves to be .004, right intake was .002 and left was .0015. A little tight but enough to worry about? Does look like a pain but I believe I will presue it and take it out of the loop. What do you know about these type of carbs as far as jetting and mixture screw setting with only a K&N filter beyond stock? Turns on mixture screw? Location of lixture screw? Thanks again.

 

I would say it's intake valves. On a hard ride as you described. You will be hanging an intake valve open. As the engine gets hotter metal expands. End result in this case no gap at all between your valve shim and the valve bucket.
Also Run 91 fuel as northjeepster said.
Just a K&N filter will not require you to rejet.

 

BTW
Welcome to the forum[img]i/expressions/face-icon-small-smile.gif[/img]

 

AHA! I have the exact same problem and have not been able to get rid of it. [img]i/expressions/face-icon-small-mad.gif[/img]I took it back to alba where I bought it and they said we don't know. Thanks A$$H@LES!!! Far as I can tell it is not the carb set up because I have since installed a dynojet kit and carb mount filter, however when my header nuts start coming loose it starts popping and making a racket and tightening these occasionally seems to make the "idle pop and die, start and run great" twitch go away temporarily. May want to check those header nuts.