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Old 11-25-2015, 03:28 AM   #1
twostickmutt
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Default backfiring

i just got a doodlebug that was given to me running. engine numbers come back as a '28. it runs fine until it gets hot then starts some pretty good backfiring. it has a Mallory dual point in it. there is no inline resistor in it. new points and condenser. question is do you think it needs a resistor in it and how do you tell if the coil has a built in resistor. the coil is old that's on it. (maybe the problem ? ) it has an 8 volt battery in it also. thanks for any help.

Last edited by twostickmutt; 11-25-2015 at 03:54 AM. Reason: forgot to add something
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Old 11-25-2015, 04:13 AM   #2
colin1928
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Default Re: backfiring

To check the coil measure the resistance with OHM meter on the primary side
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Old 11-25-2015, 08:08 AM   #3
Bob Bidonde
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Default Re: backfiring

Backfiring causes:
> Faulty condenser;
> Excessively lean air-fuel mixture;
> Leaking intake valve causes backfiring through the carburetor;
> Leaking exhaust valve causes backfiring through the exhaust pipe;
> Heavy deposits in one or more combustion chambers can act like a glow plug and cause detonation while a valve is open.
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Old 11-25-2015, 09:03 AM   #4
Tom Wesenberg
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Default Re: backfiring

8 volts will be harder on the coil, points, and starter. 6 volts works fine. I don't know why they thought it should have a dual point distributor, especially on a doodlebug.

Where are you located?
Is the engine enclosed with the full hood?
How hot does it get when it backfires?
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Old 11-25-2015, 10:27 AM   #5
twostickmutt
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Default Re: backfiring

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Quote:
Originally Posted by Tom Wesenberg View Post
8 volts will be harder on the coil, points, and starter. 6 volts works fine. I don't know why they thought it should have a dual point distributor, especially on a doodlebug.

Where are you located?
Is the engine enclosed with the full hood?
How hot does it get when it backfires?
i'm in western mass. tom. just a hood no sides. i should have said after it warms to operating temp. probably runs 10/15 minutes before it backfires under hardly any load on the engine.
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