How to keep fuel up to the curb after shut off.

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69KillerFish

69KillerFish

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When I start my Cuda, After very many cranking attempts, It finally starts. After turning it off and it sits cold for a while, the gas has already dropped down through line and the same process begins again. Is there some sort of advice or device about how to keep the gas from exiting down the line and keep this issue from happening again? Is there an in-line stop ball check that would keep the fuel from backing down the line?

Any advice is greatly appreciated!
 
What carb do you have & is there a thick insulating gasket between the carb and intake manifold?
What this sounds like is that the fuel is boiling away after shut down. Evaporating fuel could also contribute to this issue.
 
how long is a while? if this is after days its the gas/ethanol evaporating out the carb. If this is after 20 min or an hour its hot start fuel boiling/evaporating out of the carb. Even if the line drains back and you dont have one of the two above problems there is usually enough fuel in the bowl of the carb to start and run it long enough for the pump to prime.
 
I'm no expert but I'm wondering if you've got another problem. It's abnormal to experience a lack of fuel at the carb on each startup. I've heard of carbs that aren't vented properly siphoning gas into the intake after a warm engine is shut off.

If it's really returning to the tank I would wonder about the condition of your fuel pump and whether or not your tank is vented adequately.
 
I have the same problem. But with mine, it will shoot fuel from the accelerator pumps but doesnt seem to be enough to start it without either a bunch of cranking, OR, shooting some starting fluid in it..
 
Happy T-day to you too!

How long is 'a while'? Minutes or hours or days? Is this a stock type mechanical fuel pump? What engine: small or big block? Carb?

The mechanical fuel pumps have 2 check valves in them; 1 at the inlet and 1 at the outlet. You could very easily have bad or dirty check valve in the fuel pump.

1. Run the engine for a little bit (not too warm), shut off wait for about 5 minutes, then crack the fuel line to the carb; it ought to still have plenty of pressure in it. (OR, tee a pressure gauge into the fuel line to the carb and watch the pressure after the engine is shut off; it should stay steady for many, many minutes.)
2. After shut off, pull the air cleaner and look down into the carb without moving the throttle. There should be no fuel leaking into the carb throat.
3. Smell the oil to see if there is any odor of gasoline in it. If so, then a carb leak or a leaking fuel pump diaphragm is the cause. Needs to be fixed PRONTO before the oil gets diluted with gas; and if it is a carb leak, it is washing down cylinders with gas.
 
The fuel pump comments in post 3 are good. In addition, the carburetor bowl should hold fuel. It can only leak out or boil off. In most carbs, there is no place to leak (I think) unless the bowl is cracked. Fuel is sucked up out of the bowl by aspiration (like an insect sprayer). The Holley 1920 1 bbl has a side bowl w/ cork gasket that can leak. BTW, we don't know what carb or engine you have. A photo would help. Gas leaks would leave a dark residue.
 
Once in the carb's fuel bowl the fuel isn't able to get back to the fuel tank. Not possible in normal operating conditions. If the fuel in the line before the pump is returning to the tank you have tank venting problem. If it is after the pump you have a venting problem and bad check valve(s) in the pump.

This stuff that they call "fuel" these days is nothing like the gasoline of 20 years ago, and probably not even like that of 5 years ago. It supposedly meets the same Vapor Pressure spec as the fuels of old, but my experience with it begs to differ. I really don't think the corn lobby has done anyone any favors except for themselves.
 
Remember,, fuel in the float bowl can't drain back to the tank thru the fuel line,,

the same way water in the sink can't jump back up, and go thru the faucet..
 
EL5DEMON340 said:
how long is a while?
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That tidbit would help.

I had the same issue with mine, I installed a small draw through electric pump back by the tank. Turn it on to get the fuel up to the mechanical pump and it starts much better.

Also as mentioned, condition of the pump itself. If the diaphragm is leaking, that would be an issue. Are you smelling gas in your oil???
 
Some of the bowls have a couple of plugs in walls where machining access was needed. Those plugs can leak. When they do leak the fuel stains the intake below them.
Boil off is waaaaay more common and likely.
 
The carb is a 700 cfm Edelbrock and Edelbrock performer intake. It sounds like part of the problem is fuel boil-off. But, as I have a clear fuel filter, the fuel does not show in the filter before a cold start up. I think the fuel drains backwards after it sits for a while. If there are check balls in the mechanical fuel pump, it could be likely that there could be a problem there too. I like the idea of a draw thru electrical pump outside the tank. My Dad had a similar problem with his Lil' Red and it solved his issue. I will do some investigating soon and let you all know what I find.

Thank you all very much for your help, it is greatly appreciated.
 
a Facet style electric pump (cheap low pressure magnetic check ball pump) inline at the tank to prime the carb after a day or two is easy to install and the thing doesnt even have to run after the car is started as the mechanical pump will draw fuel right through the check ball. I had a carter that would boil the fuel right out on top of a performer intake, installed a carter electric pump and never had another problem. May want to run a phenolic spacer (1/4- 1/2) under the carb to keep it cooler, It was cooking hot to the touch whenever I felt it after a run.
 
todays gas in a carb..will evaporate in a couple days....eddy carbs are great for that since they have a small bowl volume and the accelerator pump well is higher then the bowl floor...the cure is a electric pump....

i drive my 73 duster with a eddy 600 in vegas in summer with no spacer or heat shield under it...starts right back up....but let it set for a couple days....the bowl is dry

and the gas will not drain back down the fuel line...it is not a seal vacuum inside bowl...just like a couple of water sitting in cup...does not drain back
 
You do have the "Thick Edelbrock gasket under the carb right?"
 
In this hot summer Vegas heat I too run a electric pump on a switch in case of vaporlock.Turn it on for a few seconds to feed the mechanical pump and fill the carb. after it starts switch it off and let the mechanical take over.Works for cold starts too.
 
I had an AFB on a car that would boil off just as the OP describes. The insulating carb base gaskets didn't do much for that. I ended up making a plate type insulator, ala the Z-28 DZ302 part, and that worked much, much better at slowing/stopping the boil off. It was nearly the same width and length as the intake itself. I painted the top light gray to go with the rest of the engine, and took the bottom to a nearly polished condition.
 
69KillerFish said:
The carb is a 700 cfm Edelbrock and Edelbrock performer intake. It sounds like part of the problem is fuel boil-off. But, as I have a clear fuel filter, the fuel does not show in the filter before a cold start up. I think the fuel drains backwards after it sits for a while. If there are check balls in the mechanical fuel pump, it could be likely that there could be a problem there too. I like the idea of a draw thru electrical pump outside the tank. My Dad had a similar problem with his Lil' Red and it solved his issue. I will do some investigating soon and let you all know what I find.

Thank you all very much for your help, it is greatly appreciated.
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Is there any fuel in the filter when you stop the engine? How much in the filter when idling? Ever have issues with a hot start? Sounds perhaps like time for a new fuel pump IMO with nothing remaining in the filter; but again it depends on the time frame somewhat. (And actully it is check valves, not check balls so don't take it apart looking for balls!)
 
For those that have the long cranking problem,, that's caused by empty fuel bowls and lines,, perhaps this'll help,,

The mechanical pumps use a spring to keep even pressure/suction in the line,, and maintains that suction/pressure with the engine not cranking/running.. (Ever change a fuel filter a while after the engines been running and get a shot of gas?)

What I do, and suggest you do, when you know it's "crank" time,, is crank the engine 3 or 4 revolutions,, and wait,, what's happening is the fuel is now being moved by the residual pressure supplied by the pump,, wait maybe the count of 5,, then crank 3 or 4 times and wait again, count of five,, now try pumping the gas slowly while continuing to crank,, and it'll catch ..

Cranking and cranking, doesn't increase suction cuz the pump's spring is already compressed as far as it can,, so waiting in such a manner will save battery,, with the same results,, this really helps when you got a low battery to start with..

hope that makes sense and hope it helps..
 
its a low 4psi pressure pump, but may not have volume for v8 solo use.
41-2010-8-2.jpg
 
Some carbs you can pour a little gas down the vent tubes to fill the bowls. If it has sat for a few days fill it up and then start the car.
 
Rocket said:
Some carbs you can pour a little gas down the vent tubes to fill the bowls. If it has sat for a few days fill it up and then start the car.
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I normally don't keep a 60cc syringe of gas in the glove box.:D

The adding of an electric fuel pump is a good idea IMO.
Deleating the mechanical pump is your choice.
 
inertia said:
For those that have the long cranking problem,, that's caused by empty fuel bowls and lines,, perhaps this'll help,,

The mechanical pumps use a spring to keep even pressure/suction in the line,, and maintains that suction/pressure with the engine not cranking/running.. (Ever change a fuel filter a while after the engines been running and get a shot of gas?)

What I do, and suggest you do, when you know it's "crank" time,, is crank the engine 3 or 4 revolutions,, and wait,, what's happening is the fuel is now being moved by the residual pressure supplied by the pump,, wait maybe the count of 5,, then crank 3 or 4 times and wait again, count of five,, now try pumping the gas slowly while continuing to crank,, and it'll catch ..

Cranking and cranking, doesn't increase suction cuz the pump's spring is already compressed as far as it can,, so waiting in such a manner will save battery,, with the same results,, this really helps when you got a low battery to start with..

hope that makes sense and hope it helps..
Click to expand...



Thanks for this. I am guilty of running my battery dead from trying to crank it (it was a weak battery to start, but still...).
 
There should be a check valve/ diaphragm in the mechanical fuel pump. Fuel should not drain back into the tank, of your clear filter is dry after sitting a while You might wanna replace the pump. I just replace the pump on my 68 Coronet for the same problem. Now the car can sit for weeks and still have fuel in the line.
 
inertia said:
For those that have the long cranking problem,, that's caused by empty fuel bowls and lines,, perhaps this'll help,,

The mechanical pumps use a spring to keep even pressure/suction in the line,, and maintains that suction/pressure with the engine not cranking/running.. (Ever change a fuel filter a while after the engines been running and get a shot of gas?)

What I do, and suggest you do, when you know it's "crank" time,, is crank the engine 3 or 4 revolutions,, and wait,, what's happening is the fuel is now being moved by the residual pressure supplied by the pump,, wait maybe the count of 5,, then crank 3 or 4 times and wait again, count of five,, now try pumping the gas slowly while continuing to crank,, and it'll catch ..

Cranking and cranking, doesn't increase suction cuz the pump's spring is already compressed as far as it can,, so waiting in such a manner will save battery,, with the same results,, this really helps when you got a low battery to start with..

hope that makes sense and hope it helps..
Click to expand...

This will also help keep you from smoking the starter. Years ago I had a neighbor that had a shop that rebuilt alternators & starters. I can remember Mr. Fox telling me every time I picked up a rebuilt starter from him telling me to crank it for no longer than a 4-5 count and giving it the same amount of time to "rest" and cool off. Even to this day I chuckle when I am walking thru a parking lot and hear someone just holding the key in the crank position if there ride will not start. If it does not start within a 5 second shot of the starter it probably will not start with a 30 second crank either....granted, there are exceptions but.....
 
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