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Discussion Topic:
Flathead Backfiring during acceleration
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inherited40tudor |
05-07-2016 @ 8:48 PM
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Member
Posts: 14
Joined: Nov 2012
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My flathead starts easily enough, but sputters and then pops and backfires through the exhaust during acceleration. This is happening as it sits in the driveway, not under driving load, even. It idles very nicely. It's running a crab-style distributor that was recently rebuilt with an external coil, still on 6 volt system like Henry intended. I've seen threads that discuss this issue and answers run the gamut between timing issues to fuel pump, carb problems. I'm very skeptical of fuel issues causing a backfire, so if someone thinks that's the case, please explain that in depth, if you will. I'm hoping someone, or several of you, can give me a good list of things to check that I can use to correct the problem and give it a really good tune up, as I don't know any flathead specialists in the area. Thanks in advance for any information you can provide. If all goes well, I'll be driving it in Gettysburg this Summer!!
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TomO |
05-08-2016 @ 7:42 AM
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Senior
Posts: 7256
Joined: Oct 2009
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I would check the distributor points for proper dwell and the condenser for open or poor connection.
Tom
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len47merc |
05-08-2016 @ 9:32 AM
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Senior
Posts: 1165
Joined: Oct 2013
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From your post it must be assumed that before the rebuild of the distributor the car was NOT exhibiting this backfiring behavior - correct? Assuming so, it is logical to assume that something is awry with the distributor rebuild - either dwell, timing or both. How was the distributor rebuilt and how was it set-up after the rebuild? Specifically how was the dwell and timing set - on a Sun/Allen machine or by some other means? Suggest Tom is on the right path and that you focus on ensuring the distributor is properly set-up and adjusted. Sounds like a classic timing issue (excessive advance, incorrect dwell, perhaps both) with what little info we have to go on at this point.
Steve
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40 Coupe |
05-09-2016 @ 5:40 AM
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Senior
Posts: 1678
Joined: Oct 2009
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If this problem started after installing the rebuilt distributor, double check that you have installed the spark plug wires in the correct positions.
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40topless |
06-09-2016 @ 6:29 AM
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Member
Posts: 38
Joined: Jun 2015
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I had the same problem with my 40. It wound up being a cracked distributor cap. Try that and see if that works
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deluxe40 |
06-09-2016 @ 10:19 AM
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Member
Posts: 413
Joined: Oct 2009
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Make sure that your rotor and distributor cap are a good match. The last time I ordered these two items the rotor I got hit the contacts on the inside of the new cap jarring it loose. Also, make sure that you have the 21A rotor for the crab distributor cap and not the 59A rotor for the two piece cap (which might not even fit).
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