Do you mean the bimetal spring on the heat riser valve? I have substituted a coil from an automatic choke at times, but the performance isn't great. Be sure the heat riser shaft is able to turn freely, and the flapper valve isn't damaged or burned away. The spring should be wound in a direction that routes exhaust heat toward the intake when the engine is cold, and directs exhaust gas away from the intake after warm-up.
Jerry

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