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why does my 620 keep backfiring ?


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Lack of choke when cold will do this. Needs to be richer mixture when cold because the internal parts aren't hot enough to vaporize the fuel droplets. Effectively it's running lean. The backfire through the carb is a lean backfire.


My L18 automatic is set right. Fire up on cold day and put in gear an step on the gas it backs up. Put in drive and away it goes. Nissan did not design them to run like shit in the cold. The only difference in running when the motor is cold is a slight lack of power.

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Probably electrical. Interrupted spark, the unburned gas goes into the exhaust pipe and it lit off as soon as the spark returns.


Could be dirty fouled plugs, bad wires, old dizzy cap but most likely worn out points or a loose wire on the coil.

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