Tank is now vented. Drilled a small hole through the plastic check ball in the center of cap, and now vents both ways. Have filled 3 tanks since, and no more woosh when cap is removed.
I had to install the reg, because this carb called for 3-5 psi, but I was reading 8 on my stock pump. The motorcraft 2100 likes 7-8 psi so for the stock carb this was fine.
It seems some kind of siphon effect is being created to keep pulling gas in after shut off. I ran that Holley for a year without issue every day, until there was. The strange thing is, I am running the old 2100 carb at the moment to keep me on the road, but this carb seems starved for gas. I cranked up the reg to 7.5 psi, and when running runs pretty good, but I have to full choke every morning to wake her up. Even pump the pedal 5-6 times. Found a vac leak the other day at the pcv hose inlet on the carb spacer, but replaced that and was able to go back to 2.5 turns out on the mix screws. Still needs full choke, and some pumps to wake up though. I want that Holley back on it though. Truck never ran so snappy, and smooth as it does with the Holley.

 

I also was reading something about clogged air bleeds acting similar, or some kinda anti siphon valve in there, but my knowledge on this subject is a little too scant to be sure. I believe the air bleeds are the little brass plugs with a hole in them just above, and in front of the accelerator nozzles? They are shiny clean, but for 2 of em, that are dark stained like gas is spilling out

 

Good work so far

I got to ask why the regulator on a stock fuel pump and this is a Holley carb right?
If not a Holley carb I under stand. Also what is the regulator set to for psi?

We also know it is not psi from the tank (at least pretty sure) as the cap was removed and drilled to vent.
So we know there is psi between motor driven fuel pump and carb.
The fuel pump should have check valves to work moving fuel from tank to carb other wise it would not work.
To test this more remove the hose from the inlet of the pump. I bet on psi there as the tank should be vented with the cap you have in place for testing.

If you find no psi before the pump, like I think you will find, the heat in the engine bay / fuel pump is boiling the fuel in the line between the pump and carb and making it expand.
To test if I am right redo the test a 2nd time but this time when you shut the motor off run cool water from a hose over the pump and fuel line to keep it cool.
Make sure the water is cool and it can get pretty hot if the hose is sitting out in the sun.

I have seen posts of the fuel pump getting hot and causing issues.
Now how to keep it cool will be the real question
Dave ----

ps can I see a picture or 2 how you have the regulator and fuel lines set up?
I may need to add a regulator to a project and want to see how others have done it.
Thanks

 

This is what I presume the air bleeds are. I also don't believe gas should be pouring out of these after shut down.
Not heat soak.
I can start the engine and immediately shut it off causing some kinda siphon effect to fill bowl, and into engine through the above marked ports

 

That looks like a Holley 2300 v2 carb that comes in a 350 & 500 cfm models.
I have run s few of them in the past, over 10 years ago now, with out any issues.
I got one on a 304 AMC v8 and my son on a 258 Jeep motor.
It is half of a Holley v4 carb and take the same parts.

It is strange it is coming out of there. I dont know what bleeds they are without pulling out my Holley books if I could even find them.
https://www.google.com/search?q=holl...client=gws-wiz
The only thing I can think of ATM is to make sure the bowl vent is open to vent any psi that may build up in there.

The bowl vent should be the hole to the right of the choke plate / shaft.
You will need to pull bowl off to make sure it is open or maybe try blowing down into that hole?
Thing is the psi would not have anywhere to go as the float should be closed if the bowl is full.
I like to pull the bowl off and stick something down the hole and see if I can see it in the bowl area.

I dont think the carb would have a vent whistle from the factory unless it was a Holley HP carb and even then I cant remember if mine had one or not or I added it?
If the vent is open fuel should not come out them other holes, only out the vent up higher.
Maybe the wrong gasket(s) were used?
How old it the carb? Has always done this but just now looking into the cause?

So beside this you also have the fuel level going higher when motor is hot and just shut down and the high level why the holes are spilling fuel that should not be.
Dave ----

 

Yes it's a variation of a 500cfm 2300. Same parts for the most part. The carb is about a year old, but only been used mabey 6 months of that. I've had to replace 3-50cc pump diaphragms so far that got ripped on the edge. Those blue alcohol ones. Just put the black rubber one in a few days ago. When it works, it works damn good, but seems real princess like compared to the mc2100. Never had any issues running a 48 year old 2100

Anyhow. Fuel pump is running 6psi steady, dropping to 5 psi when shut off. Gonna go replace the needle and seat real quick . Picked it up at a garage sale for a buck yesterday. I am starting to get pretty speedy with swapping carbs lately, that's for sure

 

I could not get a 2100 to run right on the 304 AMC and popped on the 2300.
A little tuning and a 50 cc pump and it ran great.

All the 2300 I had to install a 50 cc pump other wise the pump was to lean.
Think I also had to go bigger on the squirt nozzle.
Back then all they had were the black pumps or I did not know of the blue ones.

Still dose not answer why fuel comes out the idle air bleeds as per the link above?
As a WAG a wrong gasket was used or not sealing that is letting fuel, when the level is high in the bowl to flow out the air bleeds.
The carb would need to come off, apart and looked over closely to see where the bleeds come out on the carb base, the metering plate and float bowl to see if you can tell why it is happening.
I dont know if I have any Holley's I can pull apart to see if I can tell on my end as that part should be the same on all Holleys
Dave ----

 

I found this on line at FEPOWER.NET https://fepower.net/simplemachinesfo...?topic=10270.0

If I am seeing this right it looks like a combo of bad gasket and no bowl vent?
The heat makes the fuel boil and the psi go up.
No place for the psi to go as the bowl vent is not working so the psi pushes out at the weakest point, a gasket.
I dont see any other way with out the carb in hand.
Dave ----

 

3-5 psi? Holley says on page 7 .... but they set them up at 6.5 psi at sea level. I've seen them run flawless at 7 and heard / read that they'll even handle 7.5 psi.

199r7950-7rev7.pdf (holley.com)

I believe I try it without the FPR ... as being before the fuel filter, it could have some trash acting as a check valve. If your fuel pump is pumping only 6 psi, you don't need the FPR anyway. I have a FPR set for 6.5 and my pump pumps 7, but it was already mounted and it gets only filtered fuel.

And if my fuel line was hugging the block, I'd move it.

 

If it runs where it is at I would leave it for now.
Why cause other issues that he dose not need right now.

He needs to find and fix why when shut down a short time later the level in the carb bowl rises and fuel then comes out the idle bleed jets and not the bowl vent? I have never seen that before.

I truly believe the fuel rising is gas boiling in the lines between the motor fuel pump and the carb.
Dave ----

 

Well, he said he has the FPR between the fuel pump and the filter. A fuel filter holds a volume of gasoline. If the FPR is not letting back flow as the inline fuel filter and float bowl warm up, a pressure is created. I haven't dissected his FPR but trash can act as a check valve I think. It's easy to test, just bypass the FPR and that hose from there to the filter.

 

I have not taken a FPR apart but I cant see that holding fuel psi but I can see the motor driven pump holding fuel psi
Filters will flow even when installed backwards so cant see them as a issue either.
This is a vary strange problem.
Dave ----

 

Not really my thought. The filter is like a jug between the FPR and carburetor inlet needle & seat. If the FPR can for some reason, stop backflow towards the pump, if there is a building pressure between the FPR and carburetor, it would exist in the fuel line and fuel filter between them.
Yep.

 

Yes, fuel pump holds pressure ahead of it. As stated, fuel pump pumping @ 8 psi I do have the reg before the filter. I have been seeing parts of what I believe to be the pickup tube sock in the filter. Recently replaced the pick up, and old one had no sock in it. Looks like tiny wood splinters, or tiny fiberglass splinters.
Anyhow. Swapped needle and seat, no change, tested float in water, and it floats.
Can't be boiling, because it does it even if I start, and run for 2 seconds, first thing in morning.