I have a 350 chevy in my 39, mechanical stock fuel pump, and a 351c ford in my 46 , mechanical stock fuel pump. Both cars have a new edelbrock carb. same model, which I cant remember the number. The chevy motor can set for 4 months straight, and hit the key and it fires right up. The ford motor, after setting for 3 weeks, wont start without putting gas down the carb to get it running. Its not the carb because The previous 2 barrell carb I had on the ford did the same thing. ANY IDEAS? Thanks
It's not loosing prime to the pump. The fuel can't really crawl back out of the fuel bowl once it's in there. But the fuel can evaporate out of the fuel bowls and I believe this is what you are seeing. Why one car and not the other? They are different cars I guess.
What can I say, AFB's(Edelbrock) just like Chevy's. Have you pulled the top off the Ford to see if there is something unusual going on. It's got to be leaking somewhere. Unless there is a crack or corrosion that caused a hole, I don't know what would leak. Q-jets have a bolt in the bottom that leaks, but Edelbrock are a one piece bowl.
if the fuel pump on the ford is holding pressure, maybe the fuel is boiling out of the ford? did you try swapping the carbs over? shouldn't be to bad since its the same # carbs
Run a compression check on the Ford. My Nomad did same thing years ago. Turned out the engine was worn out even though it wasn't smoking, etc. I had to prime it to start it. Fresh engine, no more problem.
Talked to Edelbrock on this same issue. My Edelbrock seems to drain down after sitting for a few days but I know this is not possible. Tech. told me problem lies with fuel evaporation not the carb. New gasoline formulation is the culprit.
A compression check is an idea, I havent thought of. But when pumping the gas before starting its dry, so the bowl is empty. I was thinking maybe the fuel pump on the ford was letting fuel siphon back into the tank, but 31vicky says that cant happen. I am not sure how the fuel ports are in a edelbrock carb. Another thought, I have started the car while in storage, not really letting it get hot, but 3 weeks later the bowl is empty again, so the boiling out doesnt seem right? I havent noticed any fuel in the oil. I might block off the fuel line after shutting it off and see what that does. I have heard of a few people having to do this, but that crazy chevy motor, like I said, can set for months. Also, the same thing happened with the old 2 barrel on the ford, so swapping carbs im not sure about. thanks,
The mechanical pumps have check valves to keep fuel in them after shutdown. If one or both go bad it is possible that it is siphoning the fuel from the carb.
I"m betting there is a lot more heat on top of that FE ford motor then there is on top of that small block Chevy. I suspect the extra heat is speeding up the fuel vaporization on the Ford motor. Today's gas sucks, it will evaporate in minutes if there is any heat at all near it. Also, on those Edelbrock carbs, there are a set of plugs that cover the drilled passages in the 1 piece fuel bowl, I've seen these leak fuel. A little epoxy over the plugs will usually solve that issue. The plugs are on the bottom of the fuel bowl, between it and the throttle plate. If you remove the throttle plate, you can see the plugs. I'll still bet on the crap gas. Gene
How about you set up an experiment to show us how you think this happens or is possible. Physics will control the event. For a siphon to occur , the liquid needs to be unbroken with no air gap. The floats have an upper level that is below the inlet. That creates an air gap and no siphon can occur.
1. the same carb on both engines 2. no heat build up, he did not run them long enough 3. because I have seen it before 4. I have 45 years experience in working with carburetors 5. I have seen it many times on Q-jets where we ended up putting a fuel filter in the inlet that contained a check valve (like the Holley and Autolite red ones)
Yeah I read all of that too. I'm not questioning your experience, knowledge base, or what you've thought you observed. What I want to know is how you think the bowls get siphoned dry with an air gap that's all. Edit: there's 4 ways the gas leaves the fuel bowl. Pressure drop from a running engine, since its not running that leaves 3 1- gravity takes fuel down thru a leak 2 the fuel defies gravity and climbs an air gap and dribbles back down the hose 3. It evaporates. Granted if the hose is empty because of a bad check ball, that may give more ventilation to hasten the evaporation but that's about it and a stretch.
This could be a combination, the Ford probably is more likely to boil the fuel out of the carb. (much bigger chunk of metal to give up more heat for a longer period of time) and the fuel pump may be bleeding back causing a longer period of time to get replenishing fuel to the carb. I suspect both vehicles are boiling fuel to some extent. I currently have a carb that wants to flood on hot shut off causing a long crank to clear it out due to boil issue when parked for short periods of time.
Rick, the fuel filter with a check valve sounds like something to try. What do you recommend? Caton, I put a plastic carb spacer on the chevy,3/4", and it helped a lot with fuel boiling at hot idle. I still dont think its a boiling problem because it has dried up after being shut off and not a really hot engine. The evaporating I will have to dig a little deeper.
Do both carbs have the same float bowl vent? The float bowls only hold a few ounces of fuel (think 2 or 3 shot glasses). If one vent is open to atmosphere and the other goes to a charcoal can or other vapor catcher that may be the difference. Some Holley's had a little rubber cap on a linkage that would open when the throttle opened and vent the bowl, throttle closed... no vent and no evaporation.
Does a rubber fuel line exist close to the carb? Could pinch it off to test check valve theory. There are very small anti-siphon vents above the venturis that if clogged will siphon a lot of the bowl content into the barrels, can be seen dripping from the venturis after shut off if occurring. Still no sign of where the fuel is going? Run the engine just enough to fill the bowl, then carefully remove the carb from its' mount for leak inspection from the underside. Sounds like it might be happening fast enough to see something.
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