Ok, lets start off by saying that this little quad has been a recent nightmare. It started with the crank case vent tube nut located inside the air filter. The nut miraculously broke off at got sucked down the intake, bending the intake valve. Ok, simple fix and a whole new head was almost as cheap as the valve so i just replaced the head.

Bike ran like it was brand new for about 15mins, then it started to hesitate. I emptied the fuel take, replaced it with fresh fuel and there was no change. I then removed the carb and thoroughly cleaned it out. NO CHANGE.

So... i bought a new carb, replaced it, set the air/fuel mixture and Idle...NO CHANGE!!!. Did the simple sparkplug replacement for the third time. Still No change... Adjusted the valves to .005, still no change.

I know my way around small engine, but this thing has me stumped! It fired right up, has a perfect idle, but as soon as you hit the gas it stumbles all over itself. Let off and it's fine.

I NEED HELP before i turn it into a rolling ball off fire!

 

so is it bogging down during throttle punch or just stumbling all over itself spitting and sputtering? please check to see if the intake boot/flange has an O-Ring and it's going the right way. could possibly be a vacuum leak? have you done a starting fluid/ether or carb cleaner spray test around the intake to check for vacuum leaks? if the quad is bogging down, then i'd say the main jet needs a cleaning, a physical cleaning by removing it and rodding out the orifices and the center of the jet. just my two cents....

 

It stumbles all over itself except when idling. Idles like a dream. I thought that it might have jumped timing, but my marks are still dead on. I did try the vacuum test with no luck. I did try to clean all the jets, there was no change so i just bought a new carb since they were only $15. Did not change a thing.

 

i don't know if a rev limiter would have anything to do with this or not. i had a polaris do something similiar and i changed the CDI/voltage regulator and the problem went away. i don't know what happened there, but i am still learning about the CDI/electronic functions from Lynn's posts.

 

Got good compression? If so, sounds like it might be electrical.

 

Atv has great compression. Not sure if the voltage regulator could be the issue, but when you unplug it when it is running there is no change. Headlights is dim until you attempt to rev it up. It definitely seems like it is hitting a rev limiter.

 

dimmer at idle than when you rev it up? is your quad AC or DC? either way, we're fairly certain the problem is electrical. got a voltmeter/ohm meter?

 

I do have a volt meter. traced all the wiring this morning, and found one loose connection, but it did not change anything. Would a bad voltage regulator make it seem like it was hitting a rev limiter? I can completely disconnect the voltage regulator and there is absolutely ZERO change in it. Starts, idles and performs the same. Also, do these little CDI's have rev limiters?

 

Ok, I replaced the CDI, voltage regulator and another sparkplug, and there is still NO change! Anyone have any suggestions on what to check next? Timing looks good, maybe advance the timing? Ran fine for about 15mins when i changed the head, but now it stumbles and will only really idle.

 

you don't have to have an expensive voltmeter/ohm meter to test this stuff with. i have three of the $5 harbor freight meters. they work just fine. get one and it'll help you trace things down. then we'll go from there. i mean quads are like cars, you don't throw new coil wires, ignition system, distributor, alternators, and batteries at a car or truck because it ain't starting do you? well, quads are the same way. let's find the problem with troubleshooting techniques and a meter cause we can't see continuity or internal broken wires/wiring. please don't misconstrue my words as a mean statement or i'm getting on to you in particular. a lot of people throw money and parts at quads unnecessarily and then get mad when the problem was something small that a meter picked up on and not the "new parts" they installed. just trying to help here.