when the engine is fully warmed up, the engine seems to spit or cough through the front carb. i adjusted the valves. what else could be the problem?

 

I am having the same problem with my 650 p,some say to shim the jet needle,not shure if this is really the fix or not . What i found was dirt in the front carb,rear carb was clean..Any way what i did was to run the machine inthe shop for a few seconds,shut it down and drain the flout bowl. Did this like 10 times and it seem to get better,it is not perfect yet . Next plan is to run carb cleaner in the fuel to try to loosen up thing in the carb. If this dosnt work the next step is to pull carbs and clean them, also chek the jets and make sure the are right for the altatude you are at. GOOD LUCK.

 

It sounds like the carb is running little too lean. Hold your throttle where the intake is popping and drive for some distance. If the quad continues to pop, it is defitnietly too lean. Shimming the jet needle or replacing it with one size larger on the front carb might be the solution.

 

sounds good, but what i dont get is that my plug is black. doesnt that mean its rich?

 

Here is what you can do to verify whether you have rich or lean condition - a simple diagnostic technique. Hold the throttle at the position where the intake is popping, then gradually open the choke lever and see if the condition betters or worsens. If it betters, then you've got the lean condition. If it worsens, you've got the rich condition.

 

ok. i will try that.

 

ok so gradually opening the choke lever made it a lot better. so how many jet sizes should i go up?

 

Little more homework to do...
1). Is the engine popping even after it is fully warmed up? If so, then you need to fatten up the needle jet (actually a thinner/more tapered needle). If it runs fine after it is fully warmed up, don't do anything.
2). Is there any leak at the intake system? Spray some carb cleaner around it and if you notice any sudden/momentary rpm rising, you've got a leak there and that's why it runs lean.
3). Which carb is popping, front or rear, or both?
4). Which needle jet P/N do you have on your problem carb? If you are near my age, you will need a magnifying glass to read the number on that skinny needle which is usually a 4-letter designation on Kehin carbs something like NBZH, NBZI, NBZJ, etc. Find what you have first and ask your dealer for a next size up. Usually later the last letter in sequence is richer. So, NBZJ is richer than NBZI, and NBZI is richer than NBZH. If dealer doesn't know or doesn't have one, contact Kehin/Sudco directly. They will gladly help you out. Good Luck.

 

1. it pops and coughs when fully warmed up.
2. i was thinking there was a leak, but i havent checked yet, but i will.
3. front carb. i actually saw the stuff shooting out of the carb when i had the airfilter off.
4. i will check that later. its the long silver needle right?

thanks for all your help.

 

Yes, the needle jet is silverish and about 2~2 1/4" long, sharp eneded at the bottom and the flat end (like a typical nail head) at the top. You are lucky that you are working on a KFX700 not on the 750 which is a real PITA just get to the carb...