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Discussion Topic:
Backfiring Motor
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V8JR |
01-19-2020 @ 5:48 PM
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Member
Posts: 94
Joined: Mar 2012
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Having trouble getting '39 Ford to run smoothly. Has what sounds like backfires while under load and engine feels kind of mushy when applying throttle. Running Stromberg 97 carb and standard point ignition. Thanks for any ideas - V8JR
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MG |
01-19-2020 @ 6:56 PM
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Senior
Posts: 1251
Joined: Nov 2009
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What have you done? Did this condition just start happening all of a sudden? Have you changed anything or done anything recently to to car?
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TomO |
01-20-2020 @ 7:01 AM
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Senior
Posts: 7244
Joined: Oct 2009
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Check your spark on all 8 plugs, at idle you should have a blue, 1/2" spark when a plug wire is held near a head nut. If it is short or orange in color, your condenser could be weak or the coil could be going bad. Do you have a dwell meter or vacuum gauge? Check the vacuum for conditions shown in the diagram on this link: http://www.secondchancegarage.com/public/186.cfm
Tom
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37RAGTOPMAN |
01-20-2020 @ 10:26 AM
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Senior
Posts: 1942
Joined: Oct 2009
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try replacing the condenser , or look for loose connections,in your primary ignition wiring, back of ignition switch terminals any connections , dirty loose corroded connections, also on the resister, do you have a voltmeter ? if you have weak spark at the spark plugs, it could be the coil, I had a similar problem and ran a jumper wire across the resister and it pick up speed, do this only for a few seconds, you should have about 3 volts going to the ignition coil, hope this helps 1937RAGTOPMAN
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V8JR |
01-20-2020 @ 8:17 PM
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Member
Posts: 94
Joined: Mar 2012
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Thanks for the hints. It did start all of a sudden, It did have some wetness around the carburetor top - maybe running to rich all of a sudden? - V8JR
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supereal |
01-22-2020 @ 1:40 PM
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Senior
Posts: 6819
Joined: Oct 2009
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The usual cause of backfiring is a vacuum leak in or near the intake manifold. It can be a faulty gasket under the carb, or any connection to the manifold, such as a cracked or loose wiper hose, or the connection to the distributor for the snubber. Be sure all gaskets in the 97 carb are leak free, and the emulsion tubes aren't leaking. Those carbs are sensitive to these leaks. That is one reason they were replaced.
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