Edmunds Answers



  • zaken1 08/25/11 11:47 pm PST

    Probably the most common error in rebuilt carburetors is improper float level setting (or just neglecting to set the float level). All too many people just install the float as it comes; without concern about whether the float may have been bent, and in addition do not bother to look up the correct float level, nor to measure it. It is shameful and slovenly for someone who claims to be a mechanic to work like this.

    However; it is also possible (though unlikely) that the rubber tipped fuel inlet needle is sticking in the shut position. This could result from an old needle which was not designed to withstand the solvents in modern fuel.

    In either case; the person who rebuilt the carburetor should take responsibility for this.

  • zaken1 08/26/11 4:46 pm PST

    There is one other possible cause of this problem: If a pleated paper fuel filter element has been installed in place of the original sintered bronze filter; that paper element is directional: It should have been installed with the spring going into the carb first, and the metal end of the filter touching the spring. The open end of the filter element should be on the outside, against the threaded fitting. If the filter was installed backwards; so that the metal end is against the threaded fitting; it would cut off the fuel flow into the carb.

  • 0patience 08/26/11 10:50 pm PST

    Agree with the float.

    Check to make certain the float is installed correctly and that the needle and seat are not stuck or damaged.
    A common mistake is that the "hook" gets caught up under the float tab when installing the top body and pushes on the needle.

    The float tab pushes or releases the needle and seat, which allows fuel into the float bowl. If the tab is pushing on the needle and seat with no fuel in the bowl, then it won't allow fuel into the bowl.
    I am assuming that the needle and seat were replaced and all of the ports in the carb were cleaned out and checked?
    A proper rebulid on the carb would include completely cleaning the housing. Everything removed, the casing "dipped" and carb cleaner sprayed through every port to make certain there were no blockages.
    Replacement of the needle and seat and weighing the float to make certain it isn't either saturated (composit float) or full of fuel (brass or metal float).

  • bpile 08/31/11 12:44 pm PST

    I took off the top half of the carb to check out the float. The needle was stuck and wouldn't budge. I soaked it in carb cleaner for a few hours, put a fresh fuel filter in (the rebuilder had put the old dirty one back in) and the needle came loose.

    The float was about an 1/8" too low according to the 1962 edition I have of Motors Auto Repair Manual, so I raised the float level to the 1 19/32" speced in the manual and a 1 3/4" float drop. There is no fuel inside the float. The float/fuel filter seem to be working fine now. The bowl fills up, the accelerator pump squirts.

    But the engine still isn't getting any gas at all. It was running when the carb was taken off for the rebuild. And when you pour a little gas down the carb, it starts right up and runs until the fumes are used up, then it dies. What's wrong with this stupid carb? I thought maybe the main jet passage was plugged. But I took a turkey baster hand pump, put a little gas in it, placed it tight up against the main discharge vent that goes over the center of the venturi. When you squirt it, a 3 foot stream of gas shoots out of the jet - that's all free and clear. It's got gas to the bowl, the jet can pick it up and feed it to the engine, but it apparently doesn't. HELP.

  • 0patience 08/31/11 2:02 pm PST

    If the needle and seat was stuck, the it is highly likely that the "rebuild" job was done poorly and none of the ports were cleaned.
    If you push down on the throttle pump, does gas squirt out into the venturi/throat of the carb? If it doesn't, then something is still clogged.

    If it were me, I'd pull the carb and pull it apart and shoot carb cleaner through every port and make sure none of them are clogged.

  • zaken1 08/31/11 2:14 pm PST

    The main jet is not the source of the fuel used by the engine during starting and idling; that circuit only comes in when the throttle is opened above idle. The fuel used at idle and starting comes through the idle tube; which is a very small diameter fuel tube (probably .031" inside diameter) that hangs down into the main body from the the air horn, and picks up fuel from the main jet circuit. The idle tube is very prone to plugging up if there is any crud floating around in the carb. If you get a set of # 60 to # 80 drill bits and a pin vise to use for turning, you can clear the idle tube by running a suitable size bit into it.

    There is also an air bleed hole near the main discharge venturi, which can hinder the fuel flow if it becomes plugged; so I would spray carb cleaner through that hole.

    In addition, since the fuel from the idle circuit enters the airstream through the idle mixture screw and idle transfer slot; I would remove the idle fuel mixture screw from the bottom flange, and look into the threaded hole where that screw came from. You should be able to see a small round opening leading into the venturi. That is the idle fuel discharge opening; which can also become plugged. So spray fuel or carb cleaner into the threaded hole with your hand pump. This will clear out small particles, and if you spray hard enough; will also clear the vertical opening called the idle fuel transfer slot, which is in the venturi wall just above the idle fuel discharge hole. Then clean off the tip of the idle mixture screw, and put it back into the carb flange. It should be screwed in until it LIGHTLY bottoms, and then loosen it by 1 1/2 turns. That will be the initial mixture screw setting.

  • bpile 09/07/11 2:48 pm PST

    I looked through some troubleshooting guides and noticed "choke" at the top of these lists. So I adjusted the choke for cold start. It starts right up now and runs pretty good. I guess the float was a little too low and the needle was stuck. Then it just needed the choke adjustment.


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