Centrifugal clutch engages at idle

Discussion in '4-Stroke Engines' started by arnoldAriz, May 5, 2012.

  1. arnoldAriz

    arnoldAriz New Member

    I recently bought this Grubee 4G T Belt Drive Complete Gas Powered Engine Kit (80/10T) kit from Pirate Cycles:

    We are complete newbies with these kits, and have been slowly navigating our way through this build. After a little bit of delay from a stripped one-way bearing (we ended up welding it), we tested it out today and the engine seems to start fine and the sprocket finally turns (yay!), but the centrifugal clutch seems to engage too early and will spin the belt when the engine idles. We removed the bell to check and it looks like the clutch is functioning correctly by expanding only when we throttle. However, once the bell is on, it seems to catch on idle. We also noticed that the bell makes a slight grinding noise on the plate that holds the pulley. It looks like it is a little uneven. Not sure if that makes a difference.

    Is there any way to adjust it so that it engages at a higher RPM? After reading this: http://www.bicycle-engines.com/images/honda-cc.pdf we added a washer to each of the shoes. But I am not sure that it made a difference. Do we just need to add more washers? We also read that there might be an adjustment screw somewhere, but the only screw that could logically be an adjustment screw to us seems to tighten automatically when the clutch spins.

    I have searched and am not really seeing this issue answered anywhere else online. Any advice would be helpful. Thanks!
    Last edited: May 5, 2012

  2. The_Aleman

    The_Aleman Active Member

    First, make sure your clutch is mounted correctly. It's best to get a new .187" key with rounded end and file/grind it to fit. The keyway is metric, so this is necessary anyway. I don't recommend using the key that came with the kit! I found that out the hard way. Hand-fitting a new key will help keep the clutch from wobbling around.

    Second, don't overtighten your 4G belt. If it's too tight, it can cause the clutch drum to wobble around by putting too much pressure on the drum spacer. Since it's a t-belt, it really doesn't need to be very tight. I set mine with a 1/2 to 5/8" of deflection.

    If both clutch and drum are wobbling, you'll never get the thing to idle at a stop and you'll be beating up the engine keyway and clutch inner bore. Eventually your drum will break, too - this happened to me after a year of battling the same issue you're having. I ended up buying a new clutch, drum, and spending a lot of time hand-fitting a key properly.

    It's also possible you have a defective clutch. My first clutch always engaged at idle and the only way I could have fixed it was to put in higher-rate springs. As far as I know, the newer clutches are much better, as I don't have any problems with mine engaging at idle. Also never ever rev up the engine with clutch attached and drum removed! You will possibly ruin your clutch and put yourself in serious harm's way. You might want to get a replacement clutch since you've already done that.
  3. abikerider

    abikerider Member

    I had similar problems with mine. Here's a youtube video of mine acting up.


    I put stronger springs from the hardware store in which helped but it still liked to catch a little at idle. I put thick flattened lock washers in for spacers and then it wouldn't engage because the washers were too thick. I couldn't find thin washers that would fit and got tired of playing with it and bought an EZ Motorbike Q-matic and never looked back. I never tried buying a new clutch so maybe Aleman is right and they've fixed the problem with the newer clutches. Good luck.
  4. arnoldAriz

    arnoldAriz New Member


    Thank you both so much for the help!

    As it turns out, it makes a HUGE difference if you don't put the clutch on backwards. The clutch bell/drum fits SO MUCH BETTER! (actually works)

    Next, I learned it's bad to attempt to ride with the choke always on.

    In my defense, the instructions that came with the engine had small black and white pictures that were hard to see, and the choke is never located in them, or shown in an on or off position.

    Trial and error!
  5. MikeJ

    MikeJ Member

    Hey arnoldAriz -

    Welcome to this forum. "Lessons Learned" are always good to post, regardless of how one learns them. You fit right in already.
  6. arnoldAriz

    arnoldAriz New Member


    Another lesson learned:

    When you remove the clutch you installed backwards to correct it, you will likely wear out the key that holds it in place, and it will come out while riding.

    Get extra keys.