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EFV-8 Club Forum / General Ford Discussion / 1941 convertible backfire to carb, with video

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Discussion Topic: 1941 convertible backfire to carb, with video -- page: 1 2

durk

10-07-2020 @ 3:15 AM

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Hi,

I am new on this forum and i am from the Netherlands so sorry for my bad english.

i just bought a 1941 ford in america. The owner said it ran perfectly.
I think he and I have a different view on that.

The engine idles well. When I accelerate slowly, the engine also runs reasonably well. when I kick the gas I sometimes get a backfire or the engine throttles.
I've already turned the air nozzles and the engine will not run better because of this.

Below is a video. It is not very easy to hear.
If it is not good enough I can make another movie. (let me know)

(the rattling is the license plate holder)

https://youtu.be/LPnzcfypPlU

37RAGTOPMAN

10-07-2020 @ 7:29 AM

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HI durk
welcome to the club,
with the ENGINE OFF !
take the air cleaner off, open the choke all the way.,
look down the carb throat, use a small flash light
now push or pump the throttle linkage to full throttle,
do you see a stream of gas ,coming out of the spray jet ? you should
if not the accelerator pump is not working
you might have to replace the accelerator pump, or it maybe clogged,
the photo should be for your carburetor part number 9642 is the pump. the leather may be worn, or broken ,or dried out?
it is a fairly easy fix, to replace the accelerator pump
hope this helps 37Ragtopman Maine
do you have a FORD REPAIR MANUAL ? will make your life easier,

This message was edited by 37RAGTOPMAN on 10-7-20 @ 7:32 AM

TomO

10-07-2020 @ 8:01 AM

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Welcome to the Forum.

Backfire through the carburetor is due to a lean mixture. It can be the accelerator pump, power valve or a vacuum leak.

Check to make sure that the vacuum hose to the wind shield wiper switch is not cracked at either end or disconnect it at the intake manifold connection and plug the connection.

Use carburetor cleaner or propane gas around the base of the carburetor, around the vacuum fittings for the windshield wipers and the distributor vacuum brake to check for a vacuum leak. The engine speed will increase slightly when the cleaner or propane is aimed at a leak.

If the problem is not the accelerator pump or a vacuum leak, the carburetor needs to be rebuilt. Daytona Parts sell a kit with quality parts.

https://daytonaparts.com/?gclid=CjwKCAjwhLHaBRAGEiwAHCgG3u7nnmZGE5zNW2bf03GMKp4NJMGepuewjC_60Nk-LNP-UyMO_WbIOxoCNE0QAvD_BwE

Tom

51woodie

10-07-2020 @ 11:55 AM

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durk. Here is a link to rebuilding a carb that should be very similar to yours. There are several parts to the rebuild.

http://myflatheadford.com/charlie-price-1-of-4-holley-94-disassembly-and-inspection/

supereal

10-08-2020 @ 11:02 AM

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Backfire through the carb can also be due to a cracked or loose distributor cap, or a carbon path inside the cap which can often be difficult to see. As engine speed increases, the system power also goes up, and the increased spark can follow the path to, or between, the terminals to the plugs, causing backfire. I discovered this many years ago when I worked for a Ford dealer.

durk

10-08-2020 @ 12:08 PM

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thank you for your answer.
But if the cap is cracked or loose then the engine should run badly at full throttle right?
The engine idles perfectly and also full throttle.

The engine throttles when I suddenly go full throttle.
If I accelerate gradually, it is no problem.

The engine also wants to start very badly warm or not at all.
Know that flatheads suffer from this, but this is very extreme. If it runs for 5 minutes, it doesn't work anymore.

durk

10-08-2020 @ 12:10 PM

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just an update on this side of the ocean.

Thank you all for thinking along.

I did the following today. I was allowed to borrow parts from someone with a well-running 1940 pickup.

I transferred the spark plugs, complete ignition, fuel pump and carburettor to my engine.

And guess what. Still the same problem.

TomO

10-09-2020 @ 8:16 AM

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Theoretically you eliminated all but a vacuum leak or a cracked or loose distributor cap.

Tom

37RAGTOPMAN

10-12-2020 @ 8:34 AM

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HI 1941 CONVERTIBLE
you never said if the back fire is in the carburetor ?
or the exhaust system,?
do you have any exhaust leaks ?
you might have a intake manifold leak, you should check this also,
also take a compression test to see if the cylinders are equal, and have no valve problems,
like a broken valve spring, or sticking valves,
hope this helps, 37Ragtopman

durk

10-14-2020 @ 3:21 AM

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thanks for the comments.
The backfire is due to the carburettor, I had put this in the title, maybe not that obvious from me.

we're getting a little closer.
I currently have 3 holley 94 carburettors.

-an old loose one that was on the shelf. (the engine will not run properly on this one)

-an completely brand new one (the engine will not run properly on this one)

-a used one of a 40er v8. (with Ford logo)
(with this one he runs perfectly)

with 50 jets.

the new carburettor had 51 jets. So I thought I found the problem. Then I put 50 jets in here, unfortunately the problem was still not over.

the compression is between 70 and 110

the new carburettor is mine and the 40er is from someone else so can't leave it on the engine: D

This message was edited by durk on 10-14-20 @ 3:23 AM

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