142f rough surging idle/misfiring

Discussion in '4-Stroke Engines' started by Banzai7863, May 20, 2016.

  1. Banzai7863

    Banzai7863 New Member

    I'm new to the site, so I just wanted to say hello before I jump into my questions. I'm familiar with several contributors work and know if im seeking good advice, this is the place to get it.

    All right, with pleasantries out of the way. I have a huasheng 142f with a Grubee 4g belt drive transmission, 10t output and 48t sprocket. This is a new build with approx. 12 hours on the motor.

    The motor idles like crap. It surged quite a bit right out of the box, but has gotten worse with time. RPMs fluctuate rather severely and I can also hear it misfiring. I thought it was fuel related so I removed and cleaned the carbs, ditched the stock petcock for a straight fitting and external shutoff. I removed the exhaust box to check for obstructions and all was clear. I did a valve adjustment at my 10 hour oil change. Nothing seemed to make a difference. I have not installed the recommended upgraded spark plug, but I plan on picking one up tomorrow, while I'm out and about.

    When it misfires it sounds/feels like something is loose inside the motor. Is it possible it could be the early signs of a rod bolt problems. It almost seems as if the ignition timing is constantly fluctuating from the piston possibly being in a different position on different rotations of the crank. Perhaps from play in the connecting rod? I have also heard mention of flywheel key failure, or perhaps a misaligned magneto.

    Has anyone else experienced these symptoms and have a starting point or should I just tear into it and see what an inspection turns up?

    Any insight would be greatly appreciated.

    Attached Files:

    Last edited: May 20, 2016

  2. HeadSmess

    HeadSmess Well-Known Member

    flywheel key, though i think the key is machined into the flywheel, it isnt a separate piece to fall out and hide under the bench...

    valve clearance. its a 4-stroke after all. first thing to check is the valve clearance. (already done? hmmms)

    the carbs do not like having the idle jet removed and replaced...theres a chance the o-ring has been damaged from the factory. that little black plug under the throttle. no way to tell without removing it and running the risk of destroying it upon reinsertion! (or to replace the darn thing...its what cured mine. what got me was when i installed a standard slide carb from a pitbike, it kept misbehaving...until i left it outside next to the shed for over a year! it behaved once i put a new carb on)

    give it a decent ngk plug, cr8e i think they take. (already ordered...hmmms)

    possible the cam is not timed correctly. pull of the side cover and have a peek, the dots on the gears should line up.

    how is compression? bent valves/leaky valves...

    magneto is fairly well fixed except distance from flywheel, nothing to say it isnt faulty though...

    you need access to a timing light to check that ;)

    so many things...all you can do is check everything and eliminate things one by one.
  3. Banzai7863

    Banzai7863 New Member

    That's was my line of thinking. Just
    Thanks for the reply. That's pretty much what I thought, just tear into it for a good inspection. Just hoping someone had been down this road before and could narrow down my search
  4. Definitely check the air gap from the flywheel to your CDI. It could be hitting in there and creating a loss of spark. There seems to be quite a few CDI issues that I have noticed lately and wonder if that gap may have something to do with it.