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Old 11-27-2018, 11:09 AM   #1
V4F
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Default 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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Old 11-27-2018, 11:22 AM   #2
nick c
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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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Old 11-27-2018, 11:25 AM   #3
Will N
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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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Old 11-27-2018, 11:27 AM   #4
Kurt in NJ
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Condenser can cause such things-----
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Old 11-27-2018, 11:44 AM   #5
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Default Re: Help please

Also, could be fuel mixture too lean. ?
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Old 11-27-2018, 12:06 PM   #6
art ebeling
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It is running lean on gas, probably a blockage at the firewall or pencil filter in tank.. Start at the sediment bowl and work backwards to the gas tank. if you take a fuel line off you will most likely see the gas flow stop after a minute or so. You could verify by pulling out on the choke when the backfiring starts. Art
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Old 11-27-2018, 12:39 PM   #7
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good ideas ……….….. forgot compression was weird … #1/4 65# #2/3 50# thanks & I will peruse it .
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Old 11-27-2018, 01:37 PM   #8
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Quote:
Originally Posted by V4F View Post
good ideas ……….….. forgot compression was weird … #1/4 65# #2/3 50#
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.

Good luck,
Tom
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Old 11-27-2018, 03:35 PM   #9
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Quote:
Originally Posted by MALAK View Post
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.

Good luck,
Tom
There was discussion in a thread here a while ago as to whether it is even possible for a backfire to happen through the carby. Some argued that a BACK fire would only be the explosion of unburnt gasses in the exhaust (ie, out of the back of the engine) and that a "cough" through the carby would be a FORWARD fire. I thought it an acedemic difference but it would at least be more accurate and avoid misunderstandings.
This post reminded me of it.
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Old 11-27-2018, 01:23 PM   #10
30 Closed Cab PU
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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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Old 11-27-2018, 02:49 PM   #11
Bob C
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The head gaskets don't usually fail between 2 & 3, there's a lot of meat there.
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Old 11-27-2018, 04:41 PM   #12
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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.
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Old 11-27-2018, 06:32 PM   #13
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Quote:
Originally Posted by Bob C View Post
The head gaskets don't usually fail between 2 & 3, there's a lot of meat there.
True that.

Quote:
Originally Posted by Synchro909 View Post
There was discussion in a thread here a while ago as to whether it is even possible for a backfire to happen through the carby. Some argued that a BACK fire would only be the explosion of unburnt gasses in the exhaust (ie, out of the back of the engine) and that a "cough" through the carby would be a FORWARD fire. I thought it an acedemic difference but it would at least be more accurate and avoid misunderstandings.
This post reminded me of it.
Quote:
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back fires occasionally thru carb
Interesting.
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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Old 11-27-2018, 07:05 PM   #14
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I will send a copy of these to my friend . thank you much …………. any new ideas appreciated
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Old 11-27-2018, 07:10 PM   #15
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Default 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.
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Old 11-28-2018, 10:02 AM   #16
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Quote:
Originally Posted by Tom Wesenberg View Post
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.
Certainly checking the conensor is a great idea, but I would certainly listen to Tom. His advise to me a while back was spot on - baffles had come loose in aftermarket muffler, causing blockage. Car ran great at idle, but no power and backfiring when under power.
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Old 11-27-2018, 09:19 PM   #17
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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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Old 11-28-2018, 09:23 AM   #18
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paul , we have checked & cleaned ……… thank you
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Old 11-28-2018, 12:37 PM   #19
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Might pull the instrument panel and check the tightness of the ignition switch wires.
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Old 11-28-2018, 12:58 PM   #20
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I would chande back to original points and condenser .
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