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mso-para-margin-left:0in; line-height:115%; mso-pagination:widow-orphan; font-size:11.0pt; font-family:"Calibri","sans-serif"; mso-ascii-font-family:Calibri; mso-ascii-theme-font:minor-latin; mso-fareast-font-family:"Times New Roman"; mso-fareast-theme-font:minor-fareast; mso-hansi-font-family:Calibri; mso-hansi-theme-font:minor-latin;} </style> <![endif]--> I have a problem with my Edelbrock 600 cfm carb, with an electric choke.



If I run the car every few days all is fine but if it sits for about three days or more, it’s just like trying to start my engine that had run completely out of gas.


I thought that it must have been a float bowl issue and the carburetor was simply allowing gasoline to siphon back down into the line. Based on this assumption, I rebuilt the carb. However, the same problem occurs after sitting for a few days.


It has a Holley mechanical fuel pump, which pumps fine once the 302 engine is running. It seems that the fuel either evaporates or it physically looses fuel; back down the line, towards the mechanical fuel pump.



If I start it up every day or so there is no problem…just if it sits a few days. Then I have to crank the starter over “excessively” just to get the fuel pump to get the gas back where it is supposed to be. Once it fires up then I’m fine again. The cranking is good in the sense it gets oil pumped up into the top of the engine before it fires.... but its annoying spending sometimes close to 5 minutes trying to get the engine to fire for the first time. The ignition itself is all fine…all aftermarket MSD.


Am I missing something here? I have an inline fuel pressure gauge between the pump and carb, which holds good fuel pressure at an idle.



I even pondered over the idea of installing a one-way “check valve” but know this would nbe more of a band-aid and not the fix for the problem with my fuel system.



I wonder if there is a check valve in the fuel pump itself, which was faulty from day one…would that allow my fuel already in the carb to drain back?



I recall even rebuilding the fuel pump a few years ago. I don't recall a pump check valve being one of the parts in the repair kit....just gaskets and diaphragm parts.



(Just a side note: When I modified my engine, I disconnected and capped off the OEM fuel return line and left it in place. I no longer have the emissions charcoal can, etc, on the car. I didn’t see any need for a fuel return line…as I seem to recall it is more of a vapor return thing used with the OEM carb).
 

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What you are experiencing is E10 fuel percolation/evaporation from the fuel bowl(s) in the carb. Yours had an evaporative emissions system which would have somewhat prevented this but you defeated it.

Also, the fuel bowl level cannot return/drain past the needle and seat unless defective. It is normal for an engine to lose the fuel pressure prime after sitting a while with a mechanical pump (an electric pump supplying immediate pressure/volume).

As for cold starts, it is hard on an engine as it is basically cranking while dry. It needs an immediate start for proper initial lubrication.
 

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I had that issue and never solved the heat issue that boiled the gas after I turned the engine off on my 289. Put the Holley 570 street avenger and I never had that issue. Fuel bowls hang out on each end with a gasket between the main body. May maybe why ? I did have great performance with the 500 Eddy



Greg
 

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I had that issue and never solved the heat issue that boiled the gas after I turned the engine off on my 289. Put the Holley 570 street avenger and I never had that issue. Fuel bowls hang out on each end with a gasket between the main body. May maybe why ? I did have great performance with the 500 Eddy

Greg
Yes, and good point. Having the fuel bowl(s) separate from the main body does help (better heat dissipation). You can also use insulated carb spacers/gaskets and heat shields to hopefully help.
 

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I have the same problem with my Holley 3310 on my 460. I rarely drive the pickup since it only gets 8 mpg. That was my thought that the fuel was draining back past the needle and seat. I also rebuilt my carb, but it still acted the same. I did pick up another 8/10ths of a mpg, though.
I was wondering if there could be an imperfection on the carb side of the needle and seat that is letting the gas drain back.
If it is the E10 gas that is evaporating/boiling off, I would like to try some 100% gas and see if it still happens. There is a gas station 30 miles away that sells 100% gas. I need to run the pickup out of gas and then try the pure stuff.
 

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<!--[if gte mso 9]><xml> <o:DocumentProperties> <o:Version>12.00</o:Version> </o:DocumentProperties> <o:OfficeDocumentSettings> <o:RelyOnVML/> <o:AllowPNG/> </o:OfficeDocumentSettings> </xml><![endif]--> The formulation that makes up today’s gasoline blend contains ethanol (vs. MTBE) to enhance combustion. Ethanol boils at 160 degrees. Carburetors have atmospheric (bowl) vents and they allow fuel vapors to escape and reduce the fuel level in the carb fuel bowl(s). This is especially true after an engine, which has been running at operating temperature has been shut down. The under hood temps at this point well exceed 170 degrees and the carb will percolate most of if not all the fuel out into the atmosphere.

There is also increased chance of
vapor lock, (aka BLEND SEPARATION). This is when the fuel actually vaporizes in the steel fuel line, preventing the carb fuel bowl(s) from maintaining needed volume, leaning out and stalling the engine.

Fuel injected cars have a closed evaporative emission system and does not have these issues with the new gasoline blends.

The above text has been taken and condensed from the below website-
Bob's Studebaker Resource Website (Studebaker Avanti )


It is the most concise and easy to understand explanation I have come across.

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Today's gasoline is blended for closed system EFI.
 

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Today's gasoline is blended for closed system EFI.

I agree, and ethanol can cause problems, though because of the huge emissions concerns, volatility of gasoline is pretty tightly controlled, and rated via Reid Vapor Pressure (RVP) which is the pressure the blend would exhibit in a closed container at 100F.

For an interesting comparison, the RVP of avgas (no ethanol) is around 5.5-7, whereas the RVP of auto gasoline usually is around 9. This is set by the state on a local level depending on emissions regs and temperature/elevation - higher temperature, lower volatility for emissions concerns.

For example, in DFW TX, RVP for auto fuels is 9, but in El Paso where it's hot it's 7.

In Denver, RVP is 9 in the winter time, but 7.8 in the summer to reduce volatility because of smog considerations.

Guide on State Summer RVP Standards | Fuels and Fuel Additives | US EPA
 

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Do you mean the bowl goes bone dry - below the needle seat? Would not seem like siphoning back to the pump is the issue, if that is the case.

What about the secondary bowl? If it stays full, well, that would seem to rule out the "boil-off" theory.

I have an Autolite 4100. After rebuilding it, my primary would drain. What had happened is the gasket they gave me for the power valve was too thin. Although the valve was not blown, the gas would leak down past it. Since the PV is in the bottom of the bowl, well, that's what happened - empty bowl. Don't know how your carb compares to a 4100 but might be worth a look.

Still, 5 minutes of cranking... Have you tried connecting the pump to a small gas jug with a 2 foot section of hose? Whether it starts or doesn't should at least tell you which end of the car is the problem! Good luck

Puttster
 

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Junk the Edelbrock.
No you don't need to junk the ebrock. I have used them on mild street motors and never had a problem with one and got decent mileage and the performance was as good or better than comparable holleys on those motors. The fuel is the problem not the carb.
Cranking for five minutes is alot. The last motor I had with an ebrock after sitting for a month or more would start in less than thirty seconds. It took some pretty vigorous pumping of the pedal but always started pretty easy. I had a Carter high performance mechanical fuel pump with stock fuel lines and a large in line filter just before the carb.
 

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funny Klutz , great to see you admit no hands on or in this case no butt in .

only problem is the dirt in neddle/seat , if there was , still won't let fuel bowl go completely dry . only to the level of the seat

add. look at the seat level , not where your a$$ is park , in the carb
Look for key words MOE-RON

KULTULZ- EXACT WORDS NOT MUMBLED said:
some volume could exit the needle/seat if the pump lost it's prime.
 

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Completely normal for fuel to evaporate in a day or so. Especially on an edelbrock carb. One, the bowls don't have a big capacity. Two, they are RIGHT on top of the engine/manifold-and they run hot anyway. Once you shut it off (hot engine), the fuel is already evaporating-and quickly. Most edelbrocks will boil the fuel on a hot engine that isn't running. Usually it's not a huge problem but like with a big engine and a really hot manifold, with the carb sitting RIGHT on the intake (with a gasket between the intake & carb-but no insulating spacer), they'll boil to the point of making the engine run like poopie.

Take a quart jar and fill it 3/4 full of fuel, let it settle a minute and then mark the level of fuel in the jar with a marker. Let it sit with the lid off for a day or so and watch how fast it evaporates. I have proven this at work with my coworkers, although all I have is a pint jar. A pint almost evaporates overnight, and what's left smells like....well poo I guess you could call it. Not sure what it smells like. Old gas I guess. Also E-10 and E-15 is hydroscopic. Just like our methanol bottles-we have to keep them totally sealed or they'll suck water out of the air.

Couple things can be done if it eats at you. An electric fuel pump...turn the key on and it pumps fuel into the carb so you don't have to crank so long. A heat insulating carb spacer helps if you have the room for it. And sometimes the air filter's shape/element design/etc is conducive to allowing more vapors to escape. Usually it's the tiny marine style "filters"...aka "flame arrestors".
 

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Before anything, try a wooden clothesline clip on the fuel line (pump to carb). If it solves the issue, then heat wrap the line.
Also, when you stop and kill the engine, if the fuel is evaporating, you could hear it within about 2-3 minutes.
A half inch phenolic spacer is only $30 and a great investment imo.
Some 390's have sealed fuel pumps, which do die in funny ways. When it is running you can sometimes see fuel come out of a vent on top of the pump, meaning the diaphragm leaks.
Last ?, is the gas cap really stuck on sometimes, or seem to have some pressure released when you open it?
 

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Before anything, try a wooden clothesline clip on the fuel line (pump to carb). If it solves the issue, then heat wrap the line.
Also, when you stop and kill the engine, if the fuel is evaporating, you could hear it within about 2-3 minutes.
A half inch phenolic spacer is only $30 and a great investment imo.
Some 390's have sealed fuel pumps, which do die in funny ways. When it is running you can sometimes see fuel come out of a vent on top of the pump, meaning the diaphragm leaks.
Last ?, is the gas cap really stuck on sometimes, or seem to have some pressure released when you open it?
clothesline clip , what's the purpose of placing on fuel line ? what material is best, wood or plastic or other ?
 
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