1949 J Model Whizzer

Discussion in 'Whizzer Motorized Bicycles' started by kwaskow, May 7, 2013.

  1. kwaskow

    kwaskow New Member

    Having an issue with carburation and need some advice. My 1949 J Model Whizzer starts and runs, but only if I keep it 90% - 95% fully choked. If I back off on the choke, it dies.
    Also, since it is nearly fully choked to keep running the performance is really bad, can't keep up with my neighbor's Whizzer, and could easily beat his prior to this.
    Last edited by a moderator: Dec 15, 2015

  2. WZ507

    WZ507 Member

    If the engine requires nearly full choke to keep running the carburetor is extremely lean, or in other words the carburetor isn't providing any fuel. This could be due to either a vacuum leak or a carb issue. If there is a large vacuum leak (air entering the engine but not passing through the carb), full choke compensates for this condition by adding the maximum amount of fuel to the small amount of air going through the carb.

    What carb do you have - Tillotson ML5B, Carter (N665, N703, N704?), new Mikuni, or what? Is the carb tight on the intake port and is there a good gasket in place?

    The next thing to check is the fuel supply. If you remove the fuel line from the carb and turn on the fuel valve at the tank does gas run freely from the fuel line? If yes, the tank/line are fine. If no, figure out what's clogged or unvented.

    Next, see how the fuel flow through the carburetor is, i.e., does gas freely run out of the needle and seat when the float is lowered to the bottom of the carburetor bowl? If yes then fuel supply is fine and it is an internal issue with the carburetor. If no find out what is clogged in the needle/seat area.

    The next thing to set is the float level, but we have to know what carb it is before describing that. If the float level is very low, this can starve an engine for fuel.

    The next thing to investigate is the main jet. If it is clogged or nearly so, it will behave exactly as you describe. If the main jet is adjustable, gently seat the adjusting needle and then remove it entirely. Replace and set to the proper position - generally ~ 1.5 turns open. Start the bike and see if anything has changed. If it still requires choke to run see if it gets better and runs with less choke as you open the high speed adjustment and enrich the mixture. If things are moving in the right direction dissemble the carb and clean the high speed circuit thoroughly and this should solve the problem.