Sooooooo.....I've been struggling with a fuel delivery issue for years with my wife's '54 DeSoto flat 6 251. It has another new mechanical fuel pump (..5th one), rebuilt 1 barrel Carter Ball&Ball (..rebuilt 3 times), all new 5/16 steel line from the tank forward, super clean tank and a heat shield on the fuel pump. Here is the symptom. During the warm months it will run fine while driving but if it sits idling or is shut off and sits it will not run. It will have to cool almost completely before it will start and run. I have worked the accelerator pump during this time and no squirt. I have pulled the top carb horn and found the bowl to be dry. I have pulled the line from the pump to the carb and it is dry but the fuel bowl is full. The fuel lines are as far from a heat source as possible yet they are very hot. I am getting gas to the pump but for some reason, when hot, it won't make it to the carb. None of this problem is evident in the cooler months. I would rather run a mechanical fuel pump but would it be best to run a really good electric pump? Now, for a side note, my '51 Plymouth has a flat 6 with a mechanical fuel pump and 3 carbs and for 7 years never this issue. Any input would be very much appreciated. BloodyKnuckles
couple things... correct gas cap? for vented/not vented tank. if its vented is the vent clear, not pinched off? air leaks, vaccuum leaks, base gasket leaks, you could try giving everything a quarter turn to tight. It sounds like the gas is "boiling" somewhere along the line. The only other thing I can think of is the float level being too low so not enough gas is ever in the bowl.
did you have this problem before the fuel pump got a heat shield.is it aluminum or steel.the shield could be keeping the pump from dissipating heat.if it sheilding it from air flow.the fan will draw heat away from pump.if you decide to run an electric pump,install it near the tank.this will keep the fuel under pressure from the tank instead of a vacuum.helps with vapor lock.You can buy 6v pumps if you have 6v
I responded in the quoted text. Guys, I really appreciate your help so far. I have got to get to the bottom of this. It's getting out of control. BloodyKnuckles
Could be a perculation issue with ethanol based fuel. Try lowering the float level a bit, a couple 32nds or so. When the symptome occures are you seeing any gas around the throttle pivot on the outside of the carb? When it starts does it blow out black smoke and or soot for a second or two? If so what you are dealing with is a flooding condition, too much fuel rather than not enough. Try a hot retart with the pedal slowly pushed to the floor and held WOT while Cranking the Starter. This will allow more air in to mix withthe gas that may be puddles in the intake manifold. Also pull your plugs and take a look at them if they are sooty and or dark gray same deal. While checking the float make sure it is not leaking, pull it and shalke it listening for fuel shacking around inside. Some time a pin hole will not not pass fluid untill the fluid gets hot. Run it for a trip till it get good and hot, then as soon as you shut it down, pull the top of the float bowl and see how much fuel you have in there. Stand by with a fire ext, as if the bowl is over full it may splash gas on the hot manifold. If the is plenty lower the float level. If there is very little then check your fuel flow. Have you checked your needle and seat to assure it is clean and closing completely? If your needle valve is stuck even partially opened residual fuel pressure from the pump, and under hood temp will cause the gas inthe line from the pump to the carb to expand and over fill the float bowl if its not shutting completely. But you gotta know where the level of fuel is in the carb upon hot shut down before proceeding with further trouble shooting.
Sounds like a similar issue I had with the 52. When it got hot an loaded up it would start bucking and stuttering and then it would shut down until it completely cooled off. I had an electric fuel pump on that car too. I rebuilt the carb and it didn't give me trouble again...however I traded pretty soon afterwards so it's hard to say.
This is good advice here... My y block in the 34 does this sometimes and this technique works perfectly. I'm still curious as to how your fuel bowl could be completely empty though... Maybe you need a thick wood carburetor isolator/spacer to help prevent the fuel from boiling off? When you crank the engine does the pump not deliver fuel to the carb when this happens? That would indicate a vaporlock issue to me. BTW, I had a similar fuel delivery problem with the flat 6 in my '38 ply, turned out the fuel pickup inside the tank had cracked/broken off at some point and it just couldn't sustain the engine's fuel demand.
Are the plugs sooty, intake wet after sitting? If not, and it maybe a little bit of a stretch, but could it be a bad coil or condenser? The engine sitting, even not running may cause these items to heat soak and short if faulty? Just an idea.
Sounds like vapor lock. Try a heat shield of stainless or aluminum - copper is a great conductor of heat, and will have to opposite effect of what you are trying to accomplish (get heat away from the fuel lines). You might want to try routing a temporary fuel line through a different path (away from engine block, trans, exhaust) to see if that cures the problem. Good luck!
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