Bike motor kart questions

Discussion in 'Motorized Bicycle General Discussion' started by sorry dog, Aug 31, 2015.

  1. sorry dog

    sorry dog New Member

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    I am quite glad these forums are here since I believe you guys can really help me out with a couple of fun projects...

    1st project is a little mini kart I picked up for my kids. It's a Razor ground force that used to be low power electric, but I'm working on gas power now.

    I'd like to use the ubiquitous 66/80cc china bike motors but I foresee a couple of issues.

    Main issue is starting the engine. Short of finding a hill to coast down (not optional in Houston) I need to adapt a pull cord recoil deal or an electric start. I see some recoil start kits on ebay for $20 that list 48 to 80cc engines but will that really work with the generic 66.8

    I'm really glad these forums are here, since I could really use some help with bike engine project.

    I picked up a little razor ground force kart for the kids that used to be electric but I'm converting to gas. I'd like to use the generic 66/80cc engine that is common with the conversion kits, but I see a couple of issues with that. First is the starting... short of running down a hill to jump it, I need either a recoil rope starter or electric start setup. I see a few recoil rope starter kits that list being compatible with engines from 48-80cc. Has anybody tried to install a recoil starter on the 66cc motor?

    Next issue is the manual clutch. With it slip enough to get going from standing still and not stall the engine. Or is a centrifugal clutch going to required??

    Last major issue (for now :) ) is the mounting. To keep the chain clear of rubbing the block, I will probably have to rotate the motor 70-90 degrees back. Is it a float or diaphragm carb?? Anything else that mounting might mess up??

    I will really appreciate any opinions or advice so I can order the right parts and not waste time and money.

    I'll post pics when I'm done.... with 3hp this kart should be major fun .... for the kids of course...
     
  2. Agreen

    Agreen Member

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    The "80cc" engines are actually 66cc. So if it says 80, it's just a marketing scam. It's 66cc.

    There are pull start kits for the engines. It works for both the 48cc and 66cc engines.

    The carb bowl is float type, but you can get a 19mm walbro diaphragm style if you'd like.

    And the real problem will be the gear reduction. It needs to be geared to a really big sprocket to be usable for taking off from a stop.
     
  3. sorry dog

    sorry dog New Member

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    I don't think I'll need anywhere near the same size sprocket as bicycle since my wheel diameter is more like 4 or 6 inches vs. 26".

    I'm wondering if the clutch has enough meat to give decent modulation to start off with. The horsepower numbers I've seen are 2.8 hp for the 66cc which should be enough torque if I gear it to top out at 25 or 30.

    Any hints are where or which Walbro I should look for. Float carb is probably a no go.

    Thanks again.
     
  4. Agreen

    Agreen Member

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    Yep, a small wheel would make it easier, but I wonder if a kid could operate the clutch? If the kart is light enough, it could take off. And the pads are thick enough for that. They're probably 5/16 to 3/8" thick. It would be a lot easier with a centrifugal clutch. A 79cc harbor freight engine and a centrifugal clutch would be a better suited pair for that razor. The bike motor is designed to be bolted between a v frame. The HF engine can be mounted to a flat surface easily. Plus, those engines are normally $99, so take a 20% coupon and you got it for $80. Then put on a centrifugal clutch and you're looking about the same price for it vs a china girl. And the 79 HF engine has a gas tank on the engine, so you wouldn't look ridiculous with the peanut tank.
     
  5. Davezilla

    Davezilla New Member

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    There are centrifugal clutches for these engines but they're not as readily available as they were about a year or so ago, you can still find them but they cost almost $80 now vs the $30 price tag a few years ago.
    for the mounting, if you got a welder, no problem, but if not, the schwinn stingray mount bracket might make life a little easier. The pull starts will work on all the available engine sizes except fit the super rat type engines. The pull starts are not all created equally tho, look for the all metal ones as the ones with the plastic drum don't last too long.
    I'm all about 2 stroke engines, but if this is going to be for little kids, I gotta agree, a 79cc predator with a centrifugal clutch would probably be more practical. The stock manual clutch cannbe feathered out and released like a manual clutch but they're not very linear like a motorcycle clutch making them more tricky to launch smoothly, not impossible, but it is a different feel.
     
  6. sorry dog

    sorry dog New Member

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    I sorta had my heart set on using a 2 stroke to keep the weight down, but the $80-$100 stinger is a strong argument... same horsepower and a little easier to adapt. The weight is listed at 22 pounds. The frame itself weighs about the same.

    Mounting the China 2 stroke wasn't going to be too bad using iron pipe and unistrut. The other option I see is using 48cc engines as those can be ordered with the centrifugal clutch, but stock those are 2 hp which really isn't a while lot.
     
  7. Agreen

    Agreen Member

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    I run consistently at 35 mph on my 48 with the 44t sprocket.

    That's with matched transfers and no head gasket, but those mods are easy to do. I always recommend taking the engine completely apart to clean out any shavings before running it. Once it's apart, porting it is the next logical step.

    Where are you seeing the 48cc engine with a centrifugal clutch? Are you sure it's not a 4 stroke?
     

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