| 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
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| 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
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| 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
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| 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/
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| 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.
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| 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.
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| 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.
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| 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
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| 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
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| 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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| TomO | -- 10-14-2020 @ 7:29 AM |
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You are confusing me, you said in a previous post that you changed the carburetor, spark plugs, fuel pump and ignition system with parts from a good running car and still had the same problem. Now you say that it runs good with the carburetor from the donor car. Is the new carburetor a brand new one or a rebuilt one or just new to you? If it is brand new manufacture, who made it? Do you still have the carburetor that was on the car when you took the video? Can you post photos of the carburetors showing the side that has the fuel inlet? The photos may provide a clue to the solution to your problem. You are concerned that the engine idles fine and runs OK at cruising speeds but back fires under acceleration. I will try to help you understand what should happen under acceleration. When you accelerate the accelerator pump forces extra fuel into the air stream in the carburetor giving a richer mixture. The engine vacuum drops allowing the power valve to open and further enrich the mixture until the engine speed levels off and the vacuum rises enough to close the power valve. When the vacuum drops, the vacuum brake on the distributor rubs against the mechanical advance plate, keeping the timing from advancing. If everything works correctly the engine should accelerate smoothly. When the mixture is too lean, the engine will backfire through the carburetor, if it is too rich, you can get a backfire in the exhaust. Advanced timing can also cause this. I hope that this explanation will help you understand what is going on. Please answer my questions and post photos of the carburetors by using the "Choose File" button at the bottom of the box where you type a reply. Tom
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| durk | -- 10-15-2020 @ 3:12 AM |
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Tom, Thanks for your detailed explanation, great !! The owner of the other carburettors was confused. And had the carburettors flipped in his mind. The (Ford) carburettor comes from the 40er pickup. This is where mine runs perfectly. The other carburettor comes from a 1935 Ford and also ran well, this carburettor was removed from the egine a year ago and was on the shelf. My engine is not running well on this carburettor. (I have not posted a picture of this carburettor. It's back on the shelf.) Below the photos of the carburettors. The holley carburettor was bought new by the previous owner, he says. This one is on the engine during the movie. (the engine does not run properly) The ford carburettor comes from the 40 pickup and my engine runs well. Hope you all still get it. it might be a bit confusing! if there are any questions please let me know, will respond quickly! Thanks for your help!!! is highly valued. The photos of the Ford carburettor were taken on the pickup engine. Before anyone thinks my manifold is leaking or something ... mine is nice and clean etc. This message was edited by durk on 10-15-20 @ 3:18 AM
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| durk | -- 10-15-2020 @ 3:14 AM |
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That hole in the first 2 photos is not on the Ford carburettor. Should I maybe seal it? seald it, no difference :D tried everything but can't get the pictures upright in the forum, sorry. the exhaust fumes also smell bad. A sharp spicy air. So the mixing is not good I think?? This message was edited by durk on 10-15-20 @ 6:45 AM
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| TomO | -- 10-15-2020 @ 8:12 AM |
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The "new" carburetor is a Holley 21oo made for Ford engines in the mid 1950's. It has a vacuum port for distributor advance, which is plugged on your carburetor. Someone has added a bowl vent and it appear to have another bowl vent. These bowl vents will not cause your problem. The power valve appears to have been damaged. To check if it is leaking, fill the float bowl with fuel to just above the power valve stem and let it sit overnight. If the power valve seal is good, the fuel level should not have changed. The power valve for your engine should open when vacuum is below 6.5 inches of Mercury. There should be stampings on the side of the nut like portion of the power valve giving its rating. You should see a 6 on one surface and a 5 on the opposite side, or 65 on one side. I do not recommend that you use that carburetor, I recommend a Ford carburetor with 91-99 on the float bowl, like the 21-29 on the carburetor that makes your engine run smoothly. Other compatible carburetors have 21-29(1942 cars) or 59 (1945-1948) cars on the float bowl. With the correct power valve and a good seal on the distributor vacuum port, your engine may run fine. Tom
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| durk | -- 10-15-2020 @ 12:07 PM |
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Tom, Thanks for your response. I'll check the power valve. But also order a new one. I think it's because of the language difference. I don't quite understand what you mean by this. "vacuum port for distributor advance" What kind of seal do you mean exactly? And what is a bowl vent? ": D haha Under the manifold of the carberator is a copper pipe that is connected to the ignition for the advance. Thank you! This message was edited by durk on 10-15-20 @ 12:16 PM
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| TomO | -- 10-16-2020 @ 8:07 AM |
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The float bowl must have air ventilation to allow air to replace the fuel used. In the USA Ventilation is often shortened to vent. The 1941 Distributor vacuum brake uses direct manifold vacuum to operate. The vacuum brake allows the distributor spark to advance mechanically when driving normal, and keeps the spark from advancing under load or quick acceleration. Later Fords use a vacuum actuated advance mechanism that uses venturi vacuum to control for the advance. Venturi vacuum gives better control than manifold vacuum because it is more responsive to the throttle opening. The venturi vacuum port must be sealed so that full manifold vacuum can be built up. To check if it is sealed, spray some carburetor cleaner on the port when the engine is idling. Tom
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