Engine Trouble Idles with clutch disengaged, will not 'coast' idle

Discussion in '2-Stroke Engines' started by Rob C, Nov 13, 2016.

  1. Rob C

    Rob C New Member

    So after copious amounts of trouble shooting, rebuilds, teardowns, one broken exhaust stud and several bleeding fingers later: my motorized 66cc bike is finally running great. Doesn't bog down or 4 stroke now that I made my own gaskets out of 6 layers of aluminum sheeting.

    Problem now is that it won't coast anymore while idling. It struggles and eventually just shuts off. If I disengage the clutch and coast it will continue idling fine. It also idles fine when I sit at red lights with the clutch disengaged.

    Is it my throttle cable? The connector on the throttle handle housing is broken so the metal elbow that the throttle goes through is sort of dangling. Is that why I can't ride and idle anymore? Also, when engaging the throttle I have to rotate about a quarter turn or so before it engages at all. But this is odd because my idle screw is all the way in, so the slide should already be pretty high up in the carb.

    I had a massive exhaust leak due to their being only one bolt for about 3 days and it would still go about 10-12 mph while idling. Now it can't coast at all, like a car should when you let off the brake in an AT.

    Idle screw on my High Performance Carb is screwed all the way in. ALL the way in, cannot go any farther and backing it out more than 1.5 turns causes the engine to not even idle while stopped.

    Checked for air leaks etc. already. I mainly need to know if this is being causes by my throttle cable being too loose or whatever it may be. Is it my jet? Is it my throttle cable?

    Thanks in advance! This is my first post because this forum has so much information it hasn't been necessary yet.

    This is the carb I have. http://www.bikeberry.com/engine-kit-parts/performance/66-80cc-high-performance-carburetor.html

  2. Rob C

    Rob C New Member

    Just kinda fixed the throttle handle cable input (thing) and no changes, I just have to move my wrist less now to keep it coasting/driving while "idling".

    Also, my fuel mix is 20:1, gas to oil (5.8 ounces of oil to 116 ounces of gasoline, currently). I was told by BikeBerry that this is the right fuel mix for the break-in period. I'm on my 3rd tank now and it's almost empty. Should I change my fuel mix maybe? The engine seems to be running strong as hell and I've traveled some distance on it already.

    Also, my carb comes stock with a .78mm jet. I have no idea what I need for my engine and I haven't modified or changed the jetting. I live in Florida so you can safely assume I am at 0-50 feet above-sea-level at any given time.
    Last edited: Nov 13, 2016
  3. Rob C

    Rob C New Member

    After 9 hours of determination and severe lack of sleep I figured out the problem. The RT Carb aka Dellorto Clone has a slide inside the body of the carb that is attached to the throttle cable. The slide also controls how much air is given to engine during idle via the idle screw. Well the slide is made of soft and crappy metal and idle screw is made of stainless steel. While I was troubleshooting all the other issues I ran into, I actually wore a massive groove into the slide that controls the idle and throttle/Air-Fuel mix. The reason I wasn't idling anymore was because the slide was so low, the idle screw was sitting in a groove it made instead of raising the slide.

    Also, the reason it idled fine before was because I had a massive exhaust leak which was allowing air in the cylinder through the front instead of through the carb, which is why I didn't notice the problem.

    I ended up solving this myself but hopefully someone comes across this threadone day and I save them a couple hours of anxiety and frustration. Peace.

    TL;DR Idle screw messed up the throttle slide in my carb, bike won't idle and cruise anymore.
  4. skyash

    skyash Active Member

    I don't know about your groove .but all my hp clone carby have one from the New .

    Attached Files:

  5. skyash

    skyash Active Member

    Love how thay come on 49cc pocket bikes but are a performance upgrad for a 66cc engine.lol

    Attached Files:

  6. crassius

    crassius Well-Known Member

    I tell all my customers that it is OK to lower idle with just the screw, but to raise the idle, they should twist throttle a bit by hand while turning screw in, then check to see if it was enough - I never try to push slide up with the screw.
    gary55 likes this.
  7. gary55

    gary55 Well-Known Member

    78 seems way to big for a delorto 14 14 clone even at sea level. I would get a 74, 72, and 70. Progressively reduce size till it is happy.
  8. Rob C

    Rob C New Member

    That's how mine looks but I know for a fact it wasn't like that when I received it because I remember it being flat when I installed the throttle cable.

    According to Bike Berry, that is what it comes installed with. I have it running much better now that I changed the fuel ratio and tinkered with the carb a bit. Only extra jet I have right now is a 70, once again according to Bike Berry. From what I've read on here, jet sizes are not to be trusted 75% of the time, unless it's an official OEM's jet, like Dellorto etc.

    Isn't that hilarious? XD. Mine came with my bike kit for a very measly up-charge and so far I like it a lot. Now that I'm not ready to throw all my kit at the wall!

    Thanks for the replies guys. Much appreciated. Any extra insight or advice is always worth it to me.
  9. Rob C

    Rob C New Member

    Just road the bike about 10 miles and on my way back on one of the main streets going south my clutch cable disconnected from the handle inside the throttle housing so I had to use a hot knife to melt the plastic back around the cable end. It's amazing the little issues that pop up on these cheap ass bike kits..... Gonna order a solid aluminum throttle handle this week. Smh..