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It seems as though the gasoline we have now days evaporates many times faster than it used to. Even during the cold winter months I find my self having to crank my engine for several seconds longer to get it started after a 30 minute drive. I have been thinking about installing a hidden push button under my dashboard to power my electric fuel pump for several seconds before attempting to start my engine.
 

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I can't answer your question but I'm having the same issue with my recently re-conditioned '67 with a brand new Holley carb. If my car sits for 2 days or more it seems like the fuel, in at least the front fuel bowl, disappears enough that I've got to crank it some just to get the bowl filled. It does have the rubber vent in the top of the fuel bowl that opens when the throttle is at Idle so it certainly could be evaporation. Just don't remember this ever happening back in the '70's. :unsure:
 

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I can't answer your question but I'm having the same issue with my recently re-conditioned '67 with a brand new Holley carb. If my car sits for 2 days or more it seems like the fuel, in at least the front fuel bowl, disappears enough that I've got to crank it some just to get the bowl filled. It does have the rubber vent in the top of the fuel bowl that opens when the throttle is at Idle so it certainly could be evaporation. Just don't remember this ever happening back in the '70's. :unsure:

I'm thinking about putting a push button under my dash so I can fill my float bowls before attempting to start it. It seems as though the modern gasolines evaporate WAY faster than the gasolines of years ago.
 

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Today it got up to 53oF. We still have some snow on the ground but it's melting fast so I took the cover of my '67 and fired it up for first time in 2021. It hadn't been started for months. Prior to starting the fuel filter had 1/2" of fuel and the Primary accelerator pump was dry ... no squirting. I could see a small amount of gas in intake manifold runners. I had to crank it about 10 sec to get to where it would start and it started fine, warmed up fine and ultimately a quick jab on the gas pedal and it idled right down to a normal idle. Fuel filter was full at Idle. We've got a few more good days coming so I'm going to keep an eye on this and see if maybe the fuel on the primary side fuel bowl is leaking into the intake manifold. If it is, the Holley carb is still under warranty so it will be going back. The fact that the fuel filter only had 1/2" of fuel is making me think maybe this could just be evaporation. Anyone else have thoughts on this?
 

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Today it got up to 53oF. We still have some snow on the ground but it's melting fast so I took the cover of my '67 and fired it up for first time in 2021. It hadn't been started for months. Prior to starting the fuel filter had 1/2" of fuel and the Primary accelerator pump was dry ... no squirting. I could see a small amount of gas in intake manifold runners. I had to crank it about 10 sec to get to where it would start and it started fine, warmed up fine and ultimately a quick jab on the gas pedal and it idled right down to a normal idle. Fuel filter was full at Idle. We've got a few more good days coming so I'm going to keep an eye on this and see if maybe the fuel on the primary side fuel bowl is leaking into the intake manifold. If it is, the Holley carb is still under warranty so it will be going back. The fact that the fuel filter only had 1/2" of fuel is making me think maybe this could just be evaporation. Anyone else have thoughts on this?
I can't see any way a 4-barrel Holley could leak into the intake manifold unless the float level is a bit too high.
 

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I can't see any way a 4-barrel Holley could leak into the intake manifold unless the float level is a bit too high.
I'm not saying that these are the only reasons but based on my recent research I've found that the most likely reason for a fuel bowl to drain empty (excluding external leaks which you could see on the Intake Manifold), are Evaporation, Percolation, Power Valve or Passage Plugs. Since my car runs really good and the exhaust isn't stinking from a rich mixture, that pretty much excludes the Power Valve unless it's a very tiny leak. If it was Percolation from the carb getting too hot, especially shortly after the engine was shut down and the under hood temperature spike up, I would also have hard re-starting issues and I've never noticed that. Evaporation is still in play since fuel these days has a faster evaporation rate due to ethanol being added. The last item apparently is not an uncommon issue with Holley carbs. On the bottom of carb between the throttle plate and the horn assembly are plugs. These plugs are used to seal where they drilled into the horn assembly to make passages for the fuel to flow. These plugs can loosen up due to the constant temperature cycling of heating up and cooling down. If it's the Power Valve or these plugs there should be raw fuel laying in the runners of the intake manifold. Apparently this can be tested by taking the carb off the intake manifold and on a table/bench, fill the fuel bowls up and let it sit and then inspect for fuel leaks. If it's the Power Valve, you just replace it. If it's the plug(s) you can just put some sealer on the plugs that won't break down due to gasoline and then put it back together.

Right now I'm seeing a little raw gas laying in the Intake Manifold and I'm running some tests. I started my car and let it come up to temperature and then shut it off. My clear Fuel Filter was totally full of fuel. After 24hrs of sitting, I can see an air bubble at the top of the fuel filter but plenty of fuel still in it. Primary accelerator pump squirted fine and car started perfectly. I've removed the linkage that actuates the secondaries so I can open the secondaries without the primaries squirting fuel and inspect the Intake Runners which looked damp but no standing fuel. Now I'm going to wait 48hrs and check again. I plan on doing this until the primary accelerator won't squirt anymore. If I haven't found the problem by that time I'll take the carb off and run the bench test. Will let you know if I ever figure it out.
 

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I'm not saying that these are the only reasons but based on my recent research I've found that the most likely reason for a fuel bowl to drain empty (excluding external leaks which you could see on the Intake Manifold), are Evaporation, Percolation, Power Valve or Passage Plugs. Since my car runs really good and the exhaust isn't stinking from a rich mixture, that pretty much excludes the Power Valve unless it's a very tiny leak. If it was Percolation from the carb getting too hot, especially shortly after the engine was shut down and the under hood temperature spike up, I would also have hard re-starting issues and I've never noticed that. Evaporation is still in play since fuel these days has a faster evaporation rate due to ethanol being added. The last item apparently is not an uncommon issue with Holley carbs. On the bottom of carb between the throttle plate and the horn assembly are plugs. These plugs are used to seal where they drilled into the horn assembly to make passages for the fuel to flow. These plugs can loosen up due to the constant temperature cycling of heating up and cooling down. If it's the Power Valve or these plugs there should be raw fuel laying in the runners of the intake manifold. Apparently this can be tested by taking the carb off the intake manifold and on a table/bench, fill the fuel bowls up and let it sit and then inspect for fuel leaks. If it's the Power Valve, you just replace it. If it's the plug(s) you can just put some sealer on the plugs that won't break down due to gasoline and then put it back together.

Right now I'm seeing a little raw gas laying in the Intake Manifold and I'm running some tests. I started my car and let it come up to temperature and then shut it off. My clear Fuel Filter was totally full of fuel. After 24hrs of sitting, I can see an air bubble at the top of the fuel filter but plenty of fuel still in it. Primary accelerator pump squirted fine and car started perfectly. I've removed the linkage that actuates the secondaries so I can open the secondaries without the primaries squirting fuel and inspect the Intake Runners which looked damp but no standing fuel. Now I'm going to wait 48hrs and check again. I plan on doing this until the primary accelerator won't squirt anymore. If I haven't found the problem by that time I'll take the carb off and run the bench test. Will let you know if I ever figure it out.
Last summer I pulled into my garage, shut my engine off, took the air cleaner assembly off, and began wiping off my valve covers when I suddenly heard an odd "gurgling" noise. Then boiling gasoline began gushing out of the primary and secondary vent tubes and down into the intake manifold. I'm using an Edelbrock RPM Air Gap intake manifold that does not have an exhaust cross over passage so the aluminum intake manifold had just absorbed heat from the engine but it was still hot enough to boil the gasoline after I shut the engine off.
 

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Wow ... you certainly experienced the Percolation problem last summer and that seems really severe for not having the cross over passage. My intake is the stock aluminum manifold for an L79 engine (GM #3890490), and it does have the cross over passage but I've never noticed any issues. I've heard that putting a heat insulator between carb and manifold can help that if you've got the hood clearance. Have you done anything to fix that issue. Good luck ... John
 
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