3.5 Briggs Help Please for my kids !!!!

Discussion in 'Mechanic and Repair' started by XB 2002, Jul 7, 2008.

  1. XB 2002

    XB 2002 LawnSite Member
    Male, from St.Amant, LA
    Messages: 75

    I have a 3.5 Briggs on a Go Cart for my kids. It was given to me. The motor starts and idles OK, It seems to make a slight knocking sound at idle. It will take off and run but once warm it doesn't seem to want to take the gas and it seems to lose power. I have rebuilt the carb and changed all the gaskets. I have removed the muffler and ran it with the same results. I have made sure that the gas cap is vented. I have dumped the old fuel and put in new and it still acts the same. Compression is 110 psi. Could it be valves? I wouldn't think it would run ( idle ) as well if it was.
    Any advice my kids wouild appreciate.

    Thanks Guys *trucewhiteflag*

    XB 2002
  2. jkason

    jkason LawnSite Senior Member
    Messages: 546

    You kids will appreciate it more if you got them a GO KART MOTOR.
    One that they won't get burned on, or lose their scalp over - or covered in gasoline when it rolls over.

    Seriously. It's happened before.
  3. XB 2002

    XB 2002 LawnSite Member
    Male, from St.Amant, LA
    Messages: 75

    Dude, This is a 80's era Thunder kart with the original motor. What is a GO KART motor ? :confused::confused:
    It even has a roll cage. Why would gas spill all over them with this motor verses a GO KART motor ??

    XB 2002
  4. woop

    woop LawnSite Member
    from eire
    Messages: 2

    I think he may think its a lawn mower engine turned on its side, its not is it?

    a go kart motor would be an engine with the crank in the opposite orientation to a lawn mower engine
  5. Lawdog302

    Lawdog302 LawnSite Member
    Messages: 197

    Possibily an issue with the valves. sounds like it doesn't have enough valve lash and once it heats up it may be holding a valve open slightly, loosing compression.
  6. XB 2002

    XB 2002 LawnSite Member
    Male, from St.Amant, LA
    Messages: 75

    Thanks Guys ! And yes it is a horizontal shaft Go Kart Engine. I woulda never dreamed of someone trying to turn a vertical shaft on its side. Thanks for the replies.

    XB 2002
  7. Partsangel

    Partsangel LawnSite Member
    Messages: 80

    I think Lawdog is right, once you rule out all the other possiblilities then all you have left after an engine heats/warms up is the valve lash/clearance, your old Briggs should have .006 on the In and .009 on the Ex at TDC compression stroke. If you dont have that then take the valves out and grind the stems till you get the right clearance then continue to have Fun...Go Carts are a Blast when your young....and a Dads smile is Priceless!

  8. jkason

    jkason LawnSite Senior Member
    Messages: 546

    A go kart motor is one that has been specd specifically for karts. And not racing motors either.

    Take your typical 5 hp Briggs blower/tiller engine - looks good on a kart, right?
    That's all it's good for- looks.
    That engine stats with the 130xxx model number. The kart spec engins start with 136xxx if I remember correctly.

    When a kart rools over, the gas spills out through the tread area of the cap. The kart spec engine has a block of foam under the cap to prevent this.
    Don't think you can do this with foam at home - it will probably dissolve in the tank.
  9. khouse

    khouse LawnSite Bronze Member
    Messages: 1,465

    SO it runs great when cold? But after a while it doesn't? Check the vent in the gas cap or change it out. Did you clean out the fuel tank when you rebuilt the carb?
  10. DBFlawn

    DBFlawn LawnSite Member
    Messages: 207

    A motor with a ball bering shaft os good enough for a go cart. I have one on mine. Without the ball bering shaft you will bend the shaft

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