My buddy has a 04 KFX 400 and is having problems with it at high rpm. When you rev it high it begins to miss and his lights dim in and out with it. Does anyone know what this could be he has tried a few things but I'm not positive what they were.

 

he has had the carb off but not sure how good he is at cleaning it ? Could there just be dirt in he carb maybe??

 

Could be a clogged jet, could be he's hitting the rev limiter.

 

I would check charging system also........If not charging Could cause ignition to break down....

 

How exactly would he check the charging system? The motor is def missing it just doesnt make sense why the lights would flicker when its missing thats what has me stumped

 

Make sure the battery is fully charged around 12.5 or 12.6 volts ..test with an volt meter,,,then crank up atv check volts at idle see if volts is same or more,then increase rpm bout 5000 rpms[half throttle].Volts should go up to around 13.6 to 14.7 an start regulating an not keep increasing....Your light is prolly getting dim because of not having enough volage to run bike and lights....Just check this out an get back with us here.Good Luck..PS if volts dont increase then atv isnt charging...So you have to narrow down which part is bad....Just get back here after you try this...Also if atv is charging then we need to go to the next step....

 

Thank you for the response. My buddy just tested it and here is the message he sent me.

ok so it had 12.6. I started it and it went up to 14.4-14.7 . when i gave it gas it stayed about 14.7 but engine just started chopping like a gun almost. Sounds like its missing from about half throttle all the way to full along with light flickering

 

Well charging system sounds good right now....What does spark plug look like? Also try this...when atv is run at that bad spot take an pair of needle nose pliers an pinch off fuel line while atv is runnig an keep plier pinched off..Listen real close to engine right before engine quits with fuel pinched off [about the last 2 or 3 second] see if that bad spot clears up? if it does then an fuel problem.Well if it is an rich problem it will clear up...it doesnt than ignition problem.OR and lean problem.Please keep us updated..Good Luck...

 

he has cleaned the carb, replaced the spark plug, and got a new voltage regulator but still no luck. Originally the quad ran fine this just all of the sudden happened so the lean and/or rich problems shouldnt be possible right? I mean no parts have been changed on the quad and no adjustments have been made. I would think that most likely the jets are just clogged and the first time he cleaned the carb wasnt enough. Do jets sound most likely to you?

He also mentioned that the quad seems to be backfiring as well which it did not do before this problem

 

Sense you mention he has already had carb apart but not sure if clean good enough,,,I would clean the carb real good.also may sure that either one of the jets has been left loose an fell out,,,And if this has happened I would double check the plug..because if an jet fell out or dirt jet and him trying to ride could have fouled again THIS is easy to do....it dont take much to foul plug when engine isnt running correct,Also check the intake snorkle sometimes dirtdobbers or rat will build an nest inside restricting air flow..Also could run atv with the air cleaner lid off for an second or so the see if its needs more,,.Good Luck.