11-27-2018, 11:09 AM | #1 |
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Help please
1929 ford A pick up . mostly all stock (modern point plate) . driving along & big back fire . checked everything & can not find the problem . back fires occasionally thru carb , but has low power . things we have checked ….
1) points / timing 2) valves open / close 3) carb 4) distributor 5) moved spark lever different ways 6) it will run but not as before checked these items several times . need new ideas please ……..
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11-27-2018, 11:22 AM | #2 |
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Re: Help please
The big bang could be a bad electrical connection, it will allow raw gas to exit cylinder and enter exhaust manifold then when connection comes back you get the bang, a weak engine could be a weak condenser or a weak coil,
might do a compression check carry on nick c |
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11-27-2018, 11:25 AM | #3 |
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Re: Help please
Check the little carbon dimple in the center of the distributor cap. I've personally seen two occasions were a car started running poorly, and after checking all the things you checked, it was found that the carbon dimple was cracked or missing. From now on, that will always be the first thing I check!
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11-27-2018, 11:27 AM | #4 |
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Re: Help please
Condenser can cause such things-----
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11-27-2018, 11:44 AM | #5 |
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Re: Help please
Also, could be fuel mixture too lean. ?
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11-27-2018, 12:06 PM | #6 |
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Re: Help please
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11-27-2018, 12:39 PM | #7 |
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Re: Help please
good ideas ……….….. forgot compression was weird … #1/4 65# #2/3 50# thanks & I will peruse it .
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11-27-2018, 01:23 PM | #8 |
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Re: Help please
My father had a lot of old tractors. He would use an old riding lawn mower gas tank with a shutoff on it, disconnect the gas line at the carb, drain the carb , clean the carb filter if it had one, and substitute the mower gas tank. Run the tractor awhile, if issue was gone he knew he had a fuel issue.
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11-27-2018, 01:37 PM | #9 |
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Re: Help please
I'm guessing the head gasket is beginning to fail. When cyl 2 is on its power stroke cyl 3 is on its intake stroke and vice versa when cyl 2 is on intake cyl 3 is on power. If the hot gasses from either cylinder are crossing to the adjacent cyl the incoming air/fuel charge could be ignited. Resulting in a backfire through the carb.
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11-27-2018, 02:49 PM | #10 |
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Re: Help please
The head gaskets don't usually fail between 2 & 3, there's a lot of meat there.
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11-27-2018, 03:35 PM | #11 | |
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Re: Help please
Quote:
This post reminded me of it.
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11-27-2018, 04:41 PM | #12 |
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Re: Help please
Does it idle smooth or does it sound like one is missing ? Short one at a time to see if one is dead by listening to the RPM drop off. This is called cylinder balance test. Takes 1 ear or 2 and a screwdriver. Where it backfires is important: tailpipe or carb. If guessing is the preferred diagnostic path way based on stories of others who don't understand diagnostic procedures : go back to original points and plate in the dist. In the ideal world, Your good list would tell what test you did and what were the results and NOT just say Carb, Dist, Valves move,. By the way, even smelling the tailpipe is good information. What you learn along the way is more important than just getting it to run better. Good luck. There is pretty much a test for everything that is necessary to run.
Last edited by 100IH; 11-27-2018 at 04:57 PM. |
11-27-2018, 06:32 PM | #13 | ||
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Re: Help please
Quote:
Quote:
If we consider the fuel/air mix entering the cylinder as Forward flow wouldn't a reversal of that flow be considered a Back fire and an explosion in the exhaust, which flows the same direction as the exhaust, be considered a Forward fire? Or, in this discussion, were they looking at it from a perspective view? That is the intake (carb) is ahead of the exhaust and therefore Forward? Personally, to avoid misunderstandings, when discussing these sorts of things I think the term backfire is appropriate but should be delineated as the OP said "back fires occasionally thru carb". No ambiguity there. At least in my mind. |
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11-27-2018, 07:05 PM | #14 |
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Re: Help please
I will send a copy of these to my friend . thank you much …………. any new ideas appreciated
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11-27-2018, 07:10 PM | #15 |
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Re: Help please
Maybe we can call a firing through the carb a "front fire".
It would be rare, but a backfire could damage the exhaust or muffler baffle, and might cause an exhaust blockage. This will be noted by a smooth idle, but not revving up as it should, and the manifold vacuum will drop very low at open throttle. If you hold your hand at the tailpipe, you should feel a strong blast of exhaust when someone snaps the throttle open. In the 70's and 80's I had to repair a few exhaust with double wall pipes, where the inner layer collapsed, and couldn't be seen blocking the exhaust flow. |
11-27-2018, 09:19 PM | #16 |
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Re: Help please
I would check for carbon tracks in the distributor cap. This has happened to me more than once. The tracks are hard to see, but will allow spark which is supposed to go to one cylinder to go to the wrong place.
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11-28-2018, 09:23 AM | #17 |
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Re: Help please
paul , we have checked & cleaned ……… thank you
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11-28-2018, 10:02 AM | #18 | |
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Re: Help please
Quote:
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11-28-2018, 12:37 PM | #19 |
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Re: Help please
Might pull the instrument panel and check the tightness of the ignition switch wires.
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11-28-2018, 12:58 PM | #20 |
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Re: Help please
I would chande back to original points and condenser .
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