Fast Idle When enguaging the Clutch

Discussion in '2-Stroke Engines' started by Leroybrown420, Nov 18, 2014.

  1. Leroybrown420

    Leroybrown420 Member

    Hello Everyone.

    I have a 80cc Motorized bike that I built for off-road trail riding. I needed the bottom end torque so I installed a 62 tooth rear sprocket, extended long tube intake manifold & SHA Clone Carb. I toyed with a expansion chamber (bananna) muffler and exhaust header but was not happy with the results. I even tried a high compression cylinder head. My bike currently has a stock muffler & cylinder head. The bike has always ran good with a top speed around 20 MPH at 4,200 ft elevation.

    I have since moved to a lower & flatter elevation of 1,100 ft. I decided to swap the 62 tooth sprocket for a 40 tooth. I took the bike out and noticed the engine would redline when disengaging the clutch. The fuel in the tank was old (still running rich fuel, only have around 10 miles on this bike). Mixed up a new batch of fuel hoping for better results. No such luck. I did a quick check for air leaks and adjust the throttle cable. The cable adjustment helps some but did not solve the problem. Iv never been in love with the SHA carb and decided to install a new NT carb. Just for fun, I replaced the intake manifold gasket and added a o-ring inside the carb to help seal it up. Currently has a stock NT carb, not shown below.

    Went for a test ride, same results with the new carb and gaskets. Still redlines when pulling the clutch in, but does idle down shortly afterwords. When the RPM's drop the bike idles great. My bike hauls ass, 34 MPH (caught on radar) and the engine is not even broken in yet.

    I'm going to tinker on the bike later this week and looking for for so pregame tips. I'm convinced the problem is going to be an air leak or throttle cable issue. I do have new upper and lower cylinder head gaskets and new throttle cable ready to go. I even have a stock intake manifold if needed. Could the problem be related to the long tube intake holding an auxiliary fuel/air charge? I'm also of thinking about the running the performance head and maybe the header just to keep the engine cooler. Any thoughts on the high performance head or exhaust headers? Could a clutch cause this issue? I have posted a few older photos below.

    Thanks for the help,

    028.jpg 032.jpg 012.jpg 008.jpg

  2. crassius

    crassius Well-Known Member

    sounds like an air leak, but sometimes those long intakes can foam the fuel in the bowl due to vibration and act like a leak, also could be a sticky cable or slide