Recommend a carburetor for a 3.5 hp please

Discussion in '4-Stroke Engines' started by Loose Nut, Aug 7, 2010.

  1. Loose Nut

    Loose Nut Member

    I have a 3.5 hp Horizontal shaft 4 stroke from a Sears lawn edger that I want to use, but the carburetor seems no good for use on a bike. Could you recommend a side draft carb?

    Thank you

  2. Old Bob

    Old Bob Member

    Changing from the stock carb on that engine will leave you with no govenor and risk engine damage. Those industrial engines don't like a lot of rpm with the stock rod.
  3. spad4me

    spad4me Member

    On this page is a generic side draft carb from thats dax for $29.00 plus shipping.

    His description
    TITAN XC50
    RUI124. Fits
    Honda GXH50,
    HS and more.
    Comes with
    Throttle Cable
    stop and
    Choke, Idle
    screw, Slow
    and more..
    Only $29.99

    You will have to adapt the mounting flange and the air cleaner

    You will over wind it
  4. unior

    unior Member

    Why is the stock carb unsuitable?
  5. Loose Nut

    Loose Nut Member

    Thanks Spad!

    The stock carb does seem to have what would be an accelerator pump on a car. The current carb seems only suitable to run at a set speed.

    How concerned should I really be about a govenor?

    My cars don't have govenors and I haven't hurt them (yet)
  6. GearNut

    GearNut Active Member

    These utility engines are designed to run in a narrow RPM range.
    Obviously you can force them to run at any RPM you want to.
    A car engine is designed to operate in a wide RPM range.
    Obviously you can force it to run at any RPM you want to.
    Try running either engine at an RPM range outside it's design and what will happen?
  7. Loose Nut

    Loose Nut Member

    Well said. I can't argue with any of that. I hope to putt around with this motor. If it goes up is smoke, then I'm out the $30 I have invested in the motor, and I can put a higher quality unit in it's place.

    An engine is designed to operate at a certain RPM based on the cam profile, and the flow numbers for the carb/intake/head/exhaust. Then of course it's limited to what RPM parts fail at.

    For a little project like this I can increase the flow of the carb and change the flow of the intake/head/exhaust, but not the cam. I'm not looking to make a hot rod out of a 3.5hp, but there seems to be some room to alter what RPM the peak horsepower is. Since I am changing the carb, and will need to make an intake and exaust, I mind as well clean up the ports a bit in the head.
  8. adb140275

    adb140275 Member

    gear it to run constant at 3600 rpm and bursts of 4500-5000
  9. Loose Nut

    Loose Nut Member

    Thanks!, I was just doing the math today to figure out sprocket sizes for a jack shaft to make that happen.
  10. adb140275

    adb140275 Member

    keep in mind, the bursts should last for 5-15 seconds MAX. dont do it at all if you have a newer tecumseh, and the valves will float at 4000 on an older tecumseh
  11. Loose Nut

    Loose Nut Member

    For a starting point, I had figured to have 4,000 rpm on the engine to equate to 30 mph. It should be good to make a run to the grocery store. The bike has a speedometer so I can use that to keep me from over reving the engine, if my math is all correct.