What will cause my float bowls to go dry

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Demon499

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OK Here is what I'm running. It is a Holley #4150 (750) and it was rebuilt with the Quick Fuel Tech. billet metering blocks on both sides.
Here's the problem. When the car sits for a few days both of the bowls are dry. Even the pump is dry.
And here's another thing. If you let the car sit for a half hour and then restart it, it just runs really poor. It seems like its really rich.
If you have had this problem please let me know.
Thank you...............Ted
 
WHAT YEAR MAKE MODEL is the car.

Tank (non) venting can aggravate this.

This SEEMS to be a combination of "new style" gasohol which boils and evaps more easily, heat, so, vapor lock and fuel boiling off.

There has been numerous "cures."

Make sure your line is tight, no leaks, and new connecting hoses, originally, one from tank to tube, and from tube to pump.

One guy claims a check valve fixed it, but there are check valves in the pump, so, ??

Make sure your line is run away from exhaust heat, maybe get an isolator/ spacer for the carb

WHAT I DID that helped a lot:

Got rid of the mechanical pump and went with a rear mount electric. Added a nice think heat insulator under the carb. Constructed a return line setup with a filter bult for that. Wix shows these, as do others, in both 3/8 and 5/16 metal filters with a built in 1/4" fitting which has an orifice for vapor return.

Wix vapor return: Small fitting MUST be UP. Filter can be vertical or horizontal
Amazon product ASIN B000C9UJAA
 
Modern gas is made for fuel injection. It evaporates faster than the stuff back in the day. My car does the same thing. If I don't start it for about a week, the bowls are dry.
 
Some dual plane intakes have a runner right under the H fuel bowls. They will pump heat into the bowls.....& you know the rest. A carb spacer may help.
 
As others have said, modern gas sucks even when it's non ethanol but it also varies by region.

I have the same issue with a pair of holley 4160 carbs, only the front one though, my rear one seems to behave.

The poor running on restart after a short stop is caused by the gas percolating in the carb after shutdown and making it rich. Try holding the pedal down between half and full throttle when cranking then give it a few revs to blow out the excess fuel.

To help the issue, make sure your timing curve is decent or let us know what it is. Too little timing can cause an engine to run much warmer at idle and other operating points than it should.
I've tried everything (heat shields, spacers, lower thermostat temp) except the small return line filter setup, but I'll probably be trying that soon too since this issue is so aggravating and nothing has fixed it or even changed the behavior.

I had a similar issue with an Edelbrock carb and replaced it with efi and haven't had a hot start issue since... Ymmv.
 
Mechanical pump? If so, I don't buy the evaporate horse crap. More likely scenario is the fuel pump is allowing fuel to leak through it going back to the tank.
 
Demon499 said:
If you let the car sit for a half hour and then restart it, it just runs really poor. It seems like its really rich.
If you have had this problem please let me know.
Click to expand...
Umm, maybe the carb is leaking fuel?
Black and eye watering smoke/fumes out the tailpipe?
Is your oil level going up and it smells like gas?
 
The fuel cannot leak back to the tank via the pump because the fuel bowl vent prevents it; it acts like a siphon break.
 
RustyRatRod said:
Mechanical pump? If so, I don't buy the evaporate horse crap. More likely scenario is the fuel pump is allowing fuel to leak through it going back to the tank.
Click to expand...
Are you saying the fuel from the bowl is leaking back into the tank?
 
92b said:
Are you saying the fuel from the bowl is leaking back into the tank?
Click to expand...
I'm saying it's possible, yes......or if the fuel pump diaphragm is ruptured, it could be going into the oil pan. From the carburetor down to the pump, it has gravity on its side.
 
Bewy said:
The fuel cannot leak back to the tank via the pump because the fuel bowl vent prevents it; it acts like a siphon break.
Click to expand...
Yeah, so you say. I've seen it happen. It's a HUGE stretch to say that all the fuel in the carburetor, the line going to the pump and fuel in the pump is evaporating. I don't buy that.
 
Na.. fuel can never drain back. There's a check valve in the pump.... :poke:

beefuelpumpissue 057.JPG
 
RRR,
I never said the fuel in the line drains back into the tank, but I should have been more clear: the fuel in the fuel bowl cannot leak back through the pump into the tank.
The n/seat is higher than the fuel level in the bowl. Iffff fuel was to leak back into the tank, the fuel has to be raised [ go uphill ] to get past the seat in the n/s. The moment the fuel level drops [ only has to be a fraction of an inch ], the n/seat opens & is subject to an air break coming from the bowl vent.
 
Bewy said:
RRR,
I never said the fuel in the line drains back into the tank, but I should have been more clear: the fuel in the fuel bowl cannot leak back through the pump into the tank.
The n/seat is higher than the fuel level in the bowl. Iffff fuel was to leak back into the tank, the fuel has to be raised [ go uphill ] to get past the seat in the n/s. The moment the fuel level drops [ only has to be a fraction of an inch ], the n/seat opens & is subject to an air break coming from the bowl vent.
Click to expand...
I agree. I was talking about the fuel in the line to the pump and the fuel in the pump itself.
 
92b said:
Are you saying the fuel from the bowl is leaking back into the tank?
Click to expand...
RustyRatRod said:
I'm saying it's possible, yes......or if the fuel pump diaphragm is ruptured, it could be going into the oil pan. From the carburetor down to the pump, it has gravity on its side.
Click to expand...
Are you saying now that it is not possible for fuel from the bowl to leak back to the tank?
 
92b said:
Are you saying now that it is not possible for fuel from the bowl to leak back to the tank?
Click to expand...
Only if the needle is off the seat. It should be seated when the engine stops. The faucet is shut off. Like saying that the water drains back in your well with the faucet off. :BangHead: :BangHead:
 
toolmanmike said:
Only if the needle is off the seat. It should be seated when the engine stops. The faucet is shut off. Like saying that the water drains back in your well with the faucet off. :BangHead: :BangHead:
Click to expand...
Just to be clear we are talking about fuel in the bowl Draining back into the tank on a 4150 holley. Correct?
 
Once the bowl level drains below the seat housing and an air break is formed, can the fuel continue to drain the bowl empty?
1697811620532.png
 
Here is a picture of a 4150 bowl. The float is removed to make the needle and seat easier to see. The black line across the bowl represents the fuel level. The arrow represents the opening at the needle and seat. The air gap between the fuel level and the opening at the needle and seat is where fuel would have to travel to exit the bowl and return to the tank assuming the needle and seat are open.

20231020_093546.jpg
 
Run a nitrous plate with only the fuel solenoid and give her a squirt when she needs it.

I mean unless it's a factory/ numbers type resto.
 
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