So i bought a 97 scrambler 500 not running right and cant get it running right. When i first got the quad it acted like it was hitting a rev limiter. Around quarter throttle is will act like its at top speed and start to pop and back fire. I cleaned the carb, as of today i replaced the cam and rocker arms, fuel pump, and lines. Valves were way out of spec from the previous owner and he got it just like i did and couldnt figure out what was wrong. any suggestions would be great. i have ran a volt meter on a few things and they checked out.

 

do a check on the etc to make sure it is not activating the override. should be an 1/8" gap on the throttle cable. at least that would rule it out for the limiter coming on

 

i did start to check that out, so is there a way to test the module to make sure the board in there and the switch isnt bad? and let me ask another question about the play in the throttle cable. if im pushing in on the throttle cable to give it gas then the slack would disappear so how would the slack in the cable work with the override? i know as of last night there was no slack in the cable but it looks like the switch is working per say that the cable does get stuck to override the throttle.

 

there should be 1/8" slack with no pressure on the throttle so you be able to move the cable in the housing showing its not too tight. not sure on how to set the board.

 

I'm just guessing here but if your throttle cable is adjusted to no more than 1/8" of slack and no less than 1/16" this might work. You could try taking the top off the ETC and revving the engine then touch the contacts together and see if stays revved up, drops down to an idle, or dies. AFAIK it should work.

 

It doesnt matter if its touching or not, again i bought the quad this way. Changed the cam and rockers. Cleaned the carb. Replaced vacuum lines and fuel lines. Fresh fuel. And no change at all. Bad cdi? Bad coil?? Maybe the other two flat black boxes by the fuse box/main wire panel?

 

Not sure if you got this fixed but I had a similar problem with a Yamaha Big Bear that I picked up after it had been swamped. I basically replaced numerous parts trying to fix it almost identical to the parts you changed and eventually took it to a professional mechanic to fix it. Unfortunately they didn't fix it and couldn't figure it out. That's after me paying them $400 to rebuild an already clean carb and put in a new Stator. I eventually purchased a new CDI after I had literally tried everything else and when I plugged the new CDI the ATV finally performed to perfection. Based on my experience hitting a number of forums for help most peoples experience is the CDI is either bad (no spark) or good. Not in between like this where you get some spark but it breaks up at high idle. I would say that it is worth a try if you haven already fixed it or tried a new CDI. I actually purchased a Chinese aftermarket one on Ebay for $70 because the only other option was a new OEM one.