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06-30-2013, 10:57 AM | #1 |
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Misfiring and backfiring when engine is warm
Can someone help me please, my 1930 Sport Coupe runs prefectly for about ten minutes and then suddenly begins misfiring and backfiring very badly almost bringing the car to a stop. I have checked the timing, which is perfect - the car starts on the first turn. I have checked the points to the correct gap of .20, and the condenser is brand-new. What I suspect is that the coil needs to be replaced?
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06-30-2013, 11:06 AM | #2 |
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Re: Misfiring and backfiring when engine is warm
So, did this still occur before the condenser was replaced ? Was anything done just prior to this poor running problem ? Does slowing down help ?
I would suggest checking the fuel flow and making sure the gas line doesn't protrude to far into the sediment bowl or carburetor. Also try and remove/loosen the gas cap. If the gas cap fixes it, clean the vent. |
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06-30-2013, 11:30 AM | #3 |
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Re: Misfiring and backfiring when engine is warm
Sounds like bad condenser or coil to me. "Brand new" condensers have been known to be bad right out of the package, frequently. I test condensers on the bench before installing in the car. About 1 out of 3 do not meet my criteria to be a "good" one.
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06-30-2013, 11:32 AM | #4 |
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Re: Misfiring and backfiring when engine is warm
My guess is that you are using the so called modern points and condenser setup. the modern style condensers give lots of trouble. If this is the case, I would change back to the original setup. most good model A parts houses handle the short proof A&L reproduction original style condenser. I can see no advantage to the modern setup, most use the cheapest, made in China condenser and the points are a real pain to adjust. Usually a bad condenser or coil will start to act up after warm up or at the least little strain. If the coil gets real hot when it starts acting up, have it tested or replace.
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06-30-2013, 12:03 PM | #5 | |
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Re: Misfiring and backfiring when engine is warm
Quote:
Thanks, Tom... |
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06-30-2013, 12:50 PM | #6 |
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Re: Misfiring and backfiring when engine is warm
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06-30-2013, 01:43 PM | #7 |
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Re: Misfiring and backfiring when engine is warm
The symptoms you have descibed, are those of a bad coil. It will run and start but when it heats up begins to miss and stumble.
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06-30-2013, 09:19 PM | #8 |
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Re: Misfiring and backfiring when engine is warm
When this happens, if you pull over, will it smooth out, or continue to idle rough.
Where do you set your GAV? I would suggest when this happens, open the GAV 1/4 open from where ever you have it. When you do, it will take 1-2 minutes, but see if that smooths things out. Sounds like the engine starving. Many people will tell you that you set the GAV closed, 1/4, 1/2 3/4.... It depends on the car and the day. As a guy who worked on them 'in the day' said to me, "If Henry made it adjustable, he meant it to be adjusted". check your fuel filter, and Let us know. |
06-30-2013, 11:14 PM | #9 |
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Re: Misfiring and backfiring when engine is warm
When the sluttering and backfiring starts, if I pull over the backfiring and spluttering stops, and the engine runs smooth again. If I go at a very slow speed from there on, Almost an idle speed, I don't get the spluttering and backfiring. I have tried various 1/4 turn settings if the GAV in both directions from where it normally is set, but that doesn't help at all. The fuel filter is clean.
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07-01-2013, 06:57 AM | #10 |
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Re: Misfiring and backfiring when engine is warm
Backfiring Under Load often indicates a problem in electrical/ignition/timing.
Culprits include:
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07-01-2013, 09:24 AM | #11 | |
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Re: Misfiring and backfiring when engine is warm
Quote:
Now it sounds like a fuel flow problem. I use the mesh stand up filter that fits in the cut off valve, under the tank. It could also be caused by a micro filter or too many filters that restrict the gas flow. |
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07-01-2013, 10:07 AM | #12 |
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Re: Misfiring and backfiring when engine is warm
Mr. Swoft is correct -- it definitely sounds like your engine is not getting enough fuel.
1. The fuel filter is clean ??? -- is this the fine mesh screen on top of the glass bowl, or some type of "in-bowl", or "in-line" fuel filter. 2. Because Model A's have weak flowing, gravity flow fuel. in lieu of stronger flowing fuel pumps delivering fuel, many fuel filters in Model A's do not allow enough liquid fuel to more rapidly flow through them. 3. After running 10 minutes or so, the liquid fuel inside of your filter is drained & it is full of air -- then wait a few minutes & the filter re-fills with liquid fuel; or on the other hand, if your engine runs at very low speed, the filter allows your very slow flowing fuel to run the engine slowly. Get back & many will be glad offer suggestions -- good day! |
07-01-2013, 12:15 PM | #13 |
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Re: Misfiring and backfiring when engine is warm
Ok everyone, I took messrs Chauvin and Swoft's idea and checked the fuel flow, and voila! I cleaned out the sediment bowl, then when all reassembled, turned on the gas valve under the tank, and there was no flow of fuel, but rather a very slow drip. I have removed and cleaned out the fuel pipe between tank and sediment bowl, which was very dirty, cleaned it out, refitted, and now get a really strong flow. Thanks to all who have lent advice with this problem
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07-01-2013, 12:20 PM | #14 |
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Re: Misfiring and backfiring when engine is warm
Thanks for the update!
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07-01-2013, 12:32 PM | #15 |
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Re: Misfiring and backfiring when engine is warm
Thanks for the feedback. I'm glad to hear that the problem is solved for now. You will probably need to install the stand up mesh filter that fits in the cut off valve or the problem may soon return. The second thing that I learned about the model A is that most have rust and trash in the gas tank. Back in the day (early sixties), no stand up filters were available. A friend showed me how to install a short piece of tubing in the cut off valve to keep it from drawing fuel off the bottom of the tank, where the rust and trash collects. The tube in the cut off valve solved the problem but the stand up filter is the best way to go.
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07-01-2013, 12:59 PM | #16 |
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Re: Misfiring and backfiring when engine is warm
Most electrical problems are fuel related.
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07-01-2013, 01:23 PM | #17 |
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Re: Misfiring and backfiring when engine is warm
Mr Swoft: please can I ask you to alborate on the "stand up filter" as I think that is what I need to install in the fuel tank - is this a standard item, or is it something that I need to fabricate?
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07-01-2013, 01:31 PM | #18 |
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Re: Misfiring and backfiring when engine is warm
it goes on top of the shutoff in the tank. as purdy says they work well
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07-01-2013, 03:17 PM | #19 |
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Re: Misfiring and backfiring when engine is warm
Would like to echo a most sincere appreciation for reporting "exactly" what you found.
You started out as the student asking the teachers your questions. You ended up teaching all students & all teachers mainly because suggestions to problems are many times guesses at to what may be wrong; & are not always the real solutions to all problems Just in case you order a screen like Mitch indicated in reply no. 18, and it arrives with no instructions, those that do arrive with instructions mentions that some upper inlet holes in the shut-off valve are slightly too large; however, one can wrap the male, solid bottom end part of the filter screen element with a few layers of aluminum foil for a tight, secure fit into the shut-off valve. Hope this helps. |
07-01-2013, 04:54 PM | #20 |
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Re: Misfiring and backfiring when engine is warm
The stand up filter slips into the cut off valve and stands up a couple of inches in the bottom of the tank. This wasn't an original part but is a much needed accessory. Snyders calls it a gas tank screen. Snyders part number is A-9193-T and it lists for four dollars. If you've got a snyders catalog, it is pictured on page A-133 . Probably all model A parts houses carry this part and no mods are needed. Be sure that if you get one that it is the mesh style. The micro filter style will easily clog with material that would otherwise pass through the system with no problem.
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