Starts easy enough when cold, runs rougher as it warms then requires full choke. Wont start when hot but ok again when cooled. Has new battery. Plugs, rotor,dist, startmodule, leads and coil seem ok. Observed strong spark even when hot. Turns over when hot but wont catch. Slight backfire. Any ideas? Thanks Dee

2 Answers 2


With your description it is likely a fuel system problem, the reason being is that if the choke applied when hot helps keep the engine running your likely starving the car for fuel (very lean when hot). Applying the choke reduces the air increasing the fuel to air mixture. With the cleaner off you should be able to achieve the same thing using your hands to restrict air flow (this would eliminate something in the choke circuit).

As stated it could be a vapor lock in the fuel pump (mechanical or electrical both can vapor lock).

In addition fuel lines if they are not following the manufactures stock run locations either from new line runs or an after market inline filter has been added then this also could heat and cause vapor lock.
Then there is the carburetor which can experience various problems related to heating.
I am attaching a link to a PDF of a Mazda carburetor guide that has a troubleshooting section in it that should help you go through possible carb issues.

Carburetor Training Manual


When you have a mechanical Fuel pump. May be Fuel pump does not work when hot? (I had the behavior on my carb car. I had a transparent fuel filter and saw that pump does not work when hot. It works fine in case using some additional cooling of fuel pomp. I have used a wet rag on the fuel pump for test my suggestion.)

  • 1
    Can you say more about how you figured it out? What symptoms/clues did you notice?
    – dlu
    Nov 13, 2016 at 19:51

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