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

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Posted By Discussion Topic: 1941 convertible backfire to carb, with video -- page: 1 2     TomO 10-16-2020 @ 8:07 AM reply profile send p.m. Senior Posts: 7263 Joined: Oct 2009 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 durk 10-15-2020 @ 12:07 PM reply profile send p.m. Member Posts: 7 Joined: Oct 2020 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 TomO 10-15-2020 @ 8:12 AM reply profile send p.m. Senior Posts: 7263 Joined: Oct 2009 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 durk 10-15-2020 @ 3:14 AM reply profile send p.m. Member Posts: 7 Joined: Oct 2020 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 durk 10-15-2020 @ 3:12 AM reply profile send p.m. Member Posts: 7 Joined: Oct 2020 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 TomO 10-14-2020 @ 7:29 AM reply profile send p.m. Senior Posts: 7263 Joined: Oct 2009 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 durk 10-14-2020 @ 3:21 AM reply profile send p.m. Member Posts: 7 Joined: Oct 2020 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 37RAGTOPMAN 10-12-2020 @ 8:34 AM reply profile send p.m. Senior Posts: 1969 Joined: Oct 2009 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 TomO 10-09-2020 @ 8:16 AM reply profile send p.m. Senior Posts: 7263 Joined: Oct 2009 Theoretically you eliminated all but a vacuum leak or a cracked or loose distributor cap. Tom durk 10-08-2020 @ 12:10 PM reply profile send p.m. Member Posts: 7 Joined: Oct 2020 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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