heat riser

[Deleted User]
[Deleted User]
edited November -1 in HUDSON
Will a heat riser that is stuck shut make the engine "fall on it's face" when you accelerate hard from an idle? When you hold it at a steady rpm it runs smooth. The timming seem alright, the carb has been rebuilt, new plugs points wires,etc. Starts good once it is warmed up. the choke seems to be working good. The engine is a 202.



Thanks, Barry Smedley:(

Comments

  • Jon B
    Jon B Administrator
    By "fall on its face' do you mean, there is a sudden hesitation? This could simply be a bad seal in the accelerator pump.
  • [Deleted User]
    [Deleted User]
    It kinds makes a small popping sound, then hesitates. The carb has been gone through by a pro.



    Thanks, Barry
  • junkcarfann
    junkcarfann Expert Adviser
    Jon is right...the accelerator pump is the most likely culprit.



    The popping sound is likely the result of the fuel mixture going very lean at the instant the pedal is floored. This is because the accelerator pump is not pumping a proper amount of fuel to compensate for the gulp of air the opening of the throttle caused.



    Next comes the stumble, again caused by lack of fuel.



    It really does not matter if a pro went through the carburetor. Eliminating what is the most obvious cause because someone fixed it before has stymied many mechanics in their search for the cause.



    The pump plunger is made of leather, and could be defective, or the pump bore scored, or debris is clogging the pump's fuel circuit, or the linkage is in the wrong hole (see below).



    A check of the pump prior to anything else is to do the following:

    1. Start the car so you know that fuel is in the carb bowl.

    2. Turn off the car.

    3. Take off the air cleaner.

    4. Using a FLASHLIGHT, not a match!, look down the carb throat while you

    move the gas pedal linkage rapidly through its entire range.



    You should see a good squirt of gas squirt into the throat of the carb down near its base. If you see no flow, or dribbles, the pump is not pumping.



    The next thing to check is if the plunger arm is in the hole that provides the most movement. There should be a small triangle in the accelerator pump linkage that has (usually) 3 holes.



    Could be that the pump is working ok, but the linkage is hooked to the hole that provides the least pump plunger movement, or the middle amount.



    If it is not in the hole that provides the greatest movement, take out the tiny hairpin that holds the linkage in the hole of the triangular piece, and move the linkage rod to the hole that provides the greatest movement.



    If that does not fix it, then the accelerator pump is bad, or the internal circuit that provides fuel to the pump itself is not flowing correctly.
  • [Deleted User]
    [Deleted User]
    Thanks, I will try that.



    Barry
  • Geoff
    Geoff Senior Contributor
    It's likely that the one-way check valves (tiny ball bearings) are not in place in the accelerator pump. These allow the fuel to be drawn in through the feed hole, and then block off so that the fuel is forced out the delivery hole on depression of the pedal. I had this problem with my Jet, a flat spot, and high fuel consumption, as the fule is drawn in through this port all the time. except when it's really needed!

    Geoff.
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