| flatheadfan | -- 05-07-2018 @ 4:45 AM |
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I have a ’35 and a’36. Both cars have new carbs, fuel pumps (built with alcohol resistant parts) and new fuel lines. In both cases the cars refuse to start after sitting a few days. If I direct prime they start and run without a problem. My question is this, would a one way fuel check-valve solve the problem by retaining a fuel prime? If so, where should it go; after the factory fuel pump or before? An electric fuel pump does seem to help but it takes a lot of starter effort. Is this a hopeless thing that we have to put up with using corn fuel? Tom
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| TomO | -- 05-07-2018 @ 7:40 AM |
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Your fuel pump already has a one way check valve in the input and another for the output, you don't need another. It seems like you have 2 problems, one is that the fuel is leaking from the carburetor and the other may be a failure to prime. I would discuss the carburetor problem with the supplier of the new carburetor. The carburetor should retain enough fuel in the bowl to start the car after setting a week. The failure to prime is usually caused by air leaks in the supply to the fuel pump. These can come from connections not tight enough or poorly made, clogged fuel line and from sediment bowl gaskets. I don't know how your fuel system is configured, but the best configuration is completely stock, a steel line from the gas tank to the firewall, and a flex line to the fuel pump. The fittings should be tightened securely so that the compression sleeves are compressed to make a good seal. The flex line should be a quality reproduction and tightened securely. Fuel hoses with clamps are not recommended. The fuel lines can collapse under vacuum and hose clamps may not seal the line. The sediment bowl gasket needs to be fresh and pliable and the cover should not be over-tightened as that can distort the gasket. A clogged fuel line will also give you "vapor lock" symptoms on a hot day driving above 40mph. You can check for a clogged fuel line by performing a fuel delivery test. https://www.earlyfordv8.org/forum/viewmessages.cfm?Forum=16&Topic=7440&keywords=fuel%20delivery Tom
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| 42wagon | -- 05-07-2018 @ 10:27 AM |
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Others will tell you that the check valves in the fuel pumps should take care of the problem. My experience (and it goes back before ethanol in the gas) is that if the car sits for a week or so it will lose the prime. Now I haven't done it but there is a guy who advertises in the V8 times flex hoses with a check valve built in them. If its not a universal problem then why are these hoses sold?
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| carcrazy | -- 05-07-2018 @ 12:55 PM |
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It has been my experience that even with no airleaks anywhere between the fuel tank and the carburetor, there will be no fuel in the carburetor after the vehicle has set unused for a week or more. My current vehicle has an auxilliary electric fuel pump mounted next to the fuel tank which I run before cranking the engine after long periods of non-use. Before I had an electric fuel pump, if the vehicle wouldn't start after several attempts with the choke on fully, I would use starting fluid to get the engine to fire up. Sometimes it would take three trys with the starting fluid before the engine would start up and run.
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| len47merc | -- 05-07-2018 @ 2:17 PM |
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Here goes. Agree with TomO on all of his points, especially '...the best configuration is completely stock'. A properly sealed and optimally operating flathead fuel system will NOT drain back into the tank regardless of (reasonable - multiple months) time. Proved it to myself - data showed the '47 could sit for up to 14 weeks (never tested beyond) and other than the fuel in the bowl slightly evaporating, the glass fuel bowl on the pump as well as the clear fuel filter were ALWAYS full and the car filled the modestly evaporated fuel in the carb and cranked in well under 10 seconds (the maximum time I would ever run a starter non-stop) - 5-7 seconds tops. From experience here and on equally optimized fuel systems on a '40 and a '53 I found this to be the case and do not agree at all (all due respect to 42wagon) that if a car sits for a week or so it will lose the prime. I also do not agree at all - also with all due respect to carcrazy - that it only takes a week for fuel to disappear from a carburetor in a week. Not thumping the chest here, no brag, just fact - the stock '47 sat during a planned winter test on this exact subject for 8 weeks and fired up on a winter-time full choke on the second roll over of the engine. Surprised me it wasn't the first. Return check valves are band aids at best. I've a friend who recently placed one against my recommendations on a '56 ('er, ah, blasphemy here, Chevy) - it did not fix the problem but only masked it. And didn't work. Subsequently he removed it, bit the bullet and replaced the line and all fittings all the way to the tank, new hoses, new fuel pump, professionally rebuilt carb, buttoned everything up to the original stock configuration and voila - problem solved. Bottom line fuel should not leak back into the tank. New and/or professionally/properly rebuilt carbs should not evaporate fuel as quickly as you say. Our flatheads should start on the touch of the button and if sitting for months should still fill the carb (only) and crank with no more than two 10-second runs of the starter at full choke. I'd prefer to say less than one 10-second burst but I'd likely lose the skeptics and they'll never put in the effort to prove it. I've a well-known EFV8 flathead building colleague with multiple 990+ scoring Dearborn '35s and '36s, most all of which sit for multiple months at the time without starting. I've yet to see one of them not fire up reasonably quickly with full choke and quick push in of the choke upon firing after sitting for 8-10 weeks. He reminds me of TomO with his practical, pragmatic, data-driven knowledge and advice. And it works for him too. Steve This message was edited by len47merc on 5-7-18 @ 2:29 PM
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| TomO | -- 05-08-2018 @ 7:37 AM |
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One way check valves in the flex hose are a waste of money and are sold because people will buy them. Basic law of physics a fluid will seek its level. This means that if the fuel in the line will be at the same level as the fuel in the tank as long as atmospheric pressure is applied to the line. Fluid will not flow uphill unless there is a vacuum: means that the fuel in the sediment bowl cannot travel back to the tank because the inlet to the sediment bowl is above the fluid level. If the fuel in the sediment bowl is evaporating, that means there is a source of air or an air leak. If the fuel in the carburetor disappears in a short time (less than a week) the carburetor has a leak. The Holley/Ford carburetors leak fuel from the power valve or the power valve gasket. I am not familiar enough with the Stromberg carburetor to say where they leak. A fuel pump in good condition and no air leaks on the input side should prime the carburetor in 20 seconds or less. If yours does not do this, something is wrong and a 1 way valve will not solve the problem. Tom
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| LarryK | -- 05-08-2018 @ 6:55 PM |
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I have a similar problem starting my 1939 Deluxe after sitting a week or so. I did a test. I placed a spare Ford/Holley carburetor on the bench sitting on a glass container such that if there was any leaking from the power valve it would be collected. I filled the bowl. After a week, all of the gas (10% ethanol) had evaporated. No gas collected in the glass container. There was no gas leaking from the carburetor. However, even if the carburetor bowl is empty, I believe the car should start after one or two tries. In my case, I believe that gas is draining back the fuel line towards the tank, seeking its level as TomO says. Therefore, this type of starting problem could be caused by a leaking fuel pump bowl gasket. A flex hose at the fuel pump inlet may stop the drain back but it would not be addressing the fundamental problem. Larry
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| TomO | -- 05-09-2018 @ 8:12 AM |
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Larry, try the experiment with the carburetor sitting on a white cloth or paper rag. You will be able to see the stain of the fuel on the cloth. If it is leaking from the power valve gasket, the gasket will be wet. Another experiment you can try is to put about 1/4" of fuel in your glass container, put a cover over the container and see how long it take to evaporate. The carb in my 40 Merc still had enough gas in it after sitting from the beginning of November to the end of April to give nice streams the first time I operated the accelerator pump . Steve Hansen and I are not the only ones that were able to start our cars without additional priming. Tom
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| kubes40 | -- 05-10-2018 @ 6:02 AM |
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Once again, I must agree with TomO's advice. My cars sit for a week, even longer, and the fuel is still in the carburetor for a quick start. Those fuel lines with the check valve are "snake oil" and sold to those that don't know how to repair their vehicles properly or are looking for a quick fix. If your carburetor has been properly rebuilt (PROPERLY) the fuel will sit in the bowl until it evaporates. Well beyond a week. I do tend to pull the choke when the cars are shut off, at least minimizing the exposure to the atmosphere. Mike "Kube" Kubarth
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| supereal | -- 05-16-2018 @ 2:39 PM |
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In addition to the excellent advice by my friends, it is important to remember that much of the fuel in the carb bowl will evaporate due to "heat soak" after the engine is shut off as the carb sits atop the hot intake manifold. Many, including myself, whose driving is often limited, install an electric pump back near the tank to refill the bowl and reduce the cranking time to restart. If the problem is frequent, be sure the fuel tank cap is correct. I have seen radiator caps on tanks, instead of the necessary vented cap, which reduces fuel system efficiency by allowing a vacuum to build in the tank as the fuel is used.
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