The fuel magically disappears from my carb!

[khryslerkid]

Excuse me, but do you any "Grey Poupon"?

But of course!

 

[Ranger16]

Maybe a dumb question (but sometimes it's the one you never asked) can fuel flow through a mechanical fuel pump when the engine isn't running?

I wouldn't think so. There has to be a check valve in it or it would never pump gas.

 

[ckessel]

If there is pressure on it at the inlet due to not enough or no venting in the tank then yes.

 

[moparedtn]

If there is pressure on it at the inlet due to not enough or no venting in the tank then yes.

I believe the question in this instance is can fuel flow backwards through an idle pump? We're looking at possible ways a carburetor can lose its' fuel when sitting idle.

 

[POMONAMISSEL]

its a heat transfer thing , i've had to block off the heat raiser from the heads through the intakes . then a stack of gaskets and thin metal plates to get the heat away from the carb afb type weber . and run an electric choke on the carb .

 

[khryslerkid]

I believe the question in this instance is can fuel flow backwards through an idle pump? We're looking at possible ways a carburetor can lose its' fuel when sitting idle.

In my last post I was asking when useing a electric pusher pump, say back at the tank, will gas flow through the idle mechanical pump?

The answer is yes, it will flow through a mechanical pump. I just checked a new stock fuel pump. I blew air through it with the leaver in the open position and then placed the pump in a vise and compressed the leaver and air still passed through it.

Will gas flow backwards through it? Yes, but how is gas going to flow back to the tank when the line goes up near the top of the tank?

I don't remember how many fuel pumps I've changed in the past but removing the fuel supply side, some would want to drain forever and you had to plug them, some just dribbled a bit then stopped.

This issue with no gas in the carb bowls is mainly evaporation. Under extreme heat this ethanol gas is going to dissipate rather quickly. Ethanol free gas isn't going to do this nearly as bad if not at all.

 

[moparedtn]

In my last post I was asking when useing a electric pusher pump, say back at the tank, will gas flow through the idle mechanical pump?

The answer is yes, it will flow through a mechanical pump. I just checked a new stock fuel pump. I blew air through it with the leaver in the open position and then placed the pump in a vise and compressed the leaver and air still passed through it.

I for one appreciate your "mad scientist in the laboratory" efforts here.

Will gas flow backwards through it? Yes, but how is gas going to flow back to the tank when the line goes up near the top of the tank?

No expert here, but I'd guess that since fluids seek their own level AND the carb is obviously higher off the floor than the tank is, the potential for fuel "returning" to the tank is there - especially since we now know the pump isn't going to stand in the way.

I don't remember how many fuel pumps I've changed in the past but removing the fuel supply side, some would want to drain forever and you had to plug them, some just dribbled a bit then stopped.

As many times as I've had the fuel system apart on this particular car, I can readily agree with that. I'd take the filler cap off the tank to relieve any possible pressure and the fuel would still sometimes continuously flow for a while once I took the feed line loose up front.
Other times, catch can at the ready, it would drip a couple times and quit.
Go figure....

This issue with no gas in the carb bowls is mainly evaporation. Under extreme heat this ethanol gas is going to dissipate rather quickly. Ethanol free gas isn't going to do this nearly as bad if not at all.

I'm at the point in my own diabolical lab experimentations to conclude the same, fellow scientist.

 

[moparedtn]

its a heat transfer thing , i've had to block off the heat raiser from the heads through the intakes . then a stack of gaskets and thin metal plates to get the heat away from the carb afb type weber . and run an electric choke on the carb . View attachment 512736

I do wish the engine builder for mine had used the intake gaskets that block off the exhaust crossover. From what I've read, some of these 440's are hot natured to begin with and I certainly have one of those, given the steps I had to take to tame the cooling system.
The pretty paint job the builder did on the engine is now a cooked, flaky mess on the crossover ports in the stock intake, so it's obvious the crossover isn't blocked off.
I do have a good thick insulating carb spacer under the Edelbrock/Weber/Carter clone AFB anyways (I've gotten into that habit with all of the 440's I've fooled with over the years, usually to get clearance for the choke linkage on aftermarket carbs).
I don't have the full blown shield type "apron" under the carb, though.

In the end, I guess the consensus is that the ethanol-poisoned gas is being "boiled" (actually evaporated from heat soak) right out of the carb and the AFB is more susceptible to this event than the Holleys are, due to the location of the bowls closer to the heat source.

Thanks!

 

[ckessel]

It would be interesting to see what the variance in alcohol level content in the pump gas is between the various areas of the country. Some areas sure seem to get hit harder with fuel problems. One of the things I'm going to include on the system for my car, its EFI and will have a return line with insulation/shielding etc, is a charcoal canister to catch some of the vapors when it sits. The fuel issue is not going to go away, we will have to adapt to it and come up with solutions.

 

[threewood]

From what I've read, some of these 440's are hot natured to begin with and I certainly have one of those, given the steps I had to take to tame the cooling system.

Thanks!

My 440 got so hot during break in (guessing from the exhaust) that it melted 2 of the black plastic push pins that attach the inside firewall insulation and 2 of the plastic clips for the washer hose.

It would be interesting to see what the variance in alcohol level content in the pump gas is between the various areas of the country. Some areas sure seem to get hit harder with fuel problems. One of the things I'm going to include on the system for my car, its EFI and will have a return line with insulation/shielding etc, is a charcoal canister to catch some of the vapors when it sits. The fuel issue is not going to go away, we will have to adapt to it and come up with solutions.

What sucks for me, there is no non ethanol blend fuel within 2 hours of me except for race gas. And the highest octane rated from the pump is 91.

 

[moparedtn]

It would be interesting to see what the variance in alcohol level content in the pump gas is between the various areas of the country. Some areas sure seem to get hit harder with fuel problems. One of the things I'm going to include on the system for my car, its EFI and will have a return line with insulation/shielding etc, is a charcoal canister to catch some of the vapors when it sits. The fuel issue is not going to go away, we will have to adapt to it and come up with solutions.

Better yet, if enough people understood how BAD a decision it was for Congress to pass the mandate to begin with, enough pressure could be put upon them to repeal the lousy, wasteful law.

Oh yeah, that's right, people would have to actually be interested.
Nevermind.

We're at 10% in these parts BTW.

 

[moparedtn]

My 440 got so hot during break in (guessing from the exhaust) that it melted 2 of the black plastic push pins that attach the inside firewall insulation and 2 of the plastic clips for the washer hose.

What sucks for me, there is no non ethanol blend fuel within 2 hours of me except for race gas. And the highest octane rated from the pump is 91.

I honestly can't believe some of these were issued with 22" radiators when new.
Amazing. Could the gas have been that much of a difference back then that the smaller radiators actually worked on these beasts?

BTW, if you don't have ethanol blended in your gas....that ain't a bad thing.
At all.

 

[khryslerkid]

I honestly can't believe some of these were issued with 22" radiators when new.
Amazing. Could the gas have been that much of a difference back then that the smaller radiators actually worked on these beasts?

BTW, if you don't have ethanol blended in your gas....that ain't a bad thing.
At all.

Thats just it, back when these cars were built all gas at the pumps were leaded and e-free. That fuel didn't generate the heat like this unleaded, 10% ethanol. The gas of today is designed for a fuel injection, closed fuel system, not for carburetors.

So if you are running 10% ethanol you need to protect all of the fuel system from corrosion, heat and evaporation.

Right now I'm running 91 e-free. $3.50 a gallon. I don't have it on the road yet but during break-in and several times that I've fired it up, letting it get up to full temp, there was always gas in the carbs for the next fire up. I'll have to see how it does once I get her out on the open road for a day.

 

[POMONAMISSEL]

and guys if your going through with pulling the intake/valley for a gasket change , those new one come with paper port gaskets also , use them . they help isolate the heat transfer as well . but before you fiddle with them , make a plug of alum foll and stuff them in those heat raiser ports as well . valley thin lives longer . and can be reused . hi lo mar sealant is fuel rated , great stuff . but can be tough to get so napa has a second best sealant it will keep that gasket stack sealed and reusable as well .

 

[Ranger16]

In my last post I was asking when useing a electric pusher pump, say back at the tank, will gas flow through the idle mechanical pump?

The answer is yes, it will flow through a mechanical pump. I just checked a new stock fuel pump. I blew air through it with the leaver in the open position and then placed the pump in a vise and compressed the leaver and air still passed through it.

Will gas flow backwards through it? Yes, but how is gas going to flow back to the tank when the line goes up near the top of the tank?

I just don't get this. If gas can flow backwards, how does it ever pump up to the carb? When the inlet valve is open, the outlet valve is closed, and vice versa so fuel cannot reverse flow. What am I missing?

 

[oldbee]

Pressure from the elec. pushes the check valves off their seats a little. Maybe not as far open when diaphragm is moving, but enuf for some fuel to get by.

 

[idrivemopar]

Here is my fuel experiment. I filled this bottle with fuel, black line is start of experiment and after 8, 24 and 36 hours you can see where the line ended up. So this just shows that with out adding extra heat fuel will disappear on its own via evaporation and about 25% in this experiment was gone after 36 hours. So, if you have a hot engine with a carb full of fuel, shut it off and have heat soak and carb with open vents, its no surprise that the fuel totally disappears. Even with the cap back on after 36 hours, the fuel is still evaporating.

 

[khryslerkid]

Here is my fuel experiment. I filled this bottle with fuel, black line is start of experiment and after 8, 24 and 36 hours you can see where the line ended up. So this just shows that with out adding extra heat fuel will disappear on its own via evaporation and about 25% in this experiment was gone after 36 hours. So, if you have a hot engine with a carb full of fuel, shut it off and have heat soak and carb with open vents, its no surprise that the fuel totally disappears. Even with the cap back on after 36 hours, the fuel is still evaporating.
View attachment 513485

I'm thinking it's mostly the ethanol that's evaporating too. Once that evaporates then the rate would slow some.

Thanks for the science class

 

[idrivemopar]

I totally agree with that assessment regarding the ethanol, my questions is then, how much does the volatility of the fuel decrease with evaporation.

 

[Billccm]

Kind of confirms my experience. Sitting one to three days starting is no issue. Sitting a week, or longer requires some cranking.