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Discussion Starter · #1 ·
I'm having issues with my fuel delivery on my all original 56 Bel Air with the 256 motor ... with a warm motor I'm seeing what appears to be fuel flashing or vaporizing in the fuel line downstream of the fuel pump, gas percolates and l loose level in the glass filter just upstream of carb ... I've replaced the fuel pump with a like and kind replacement 50gph 5.5psi pump ... would a higher psi/gph pump make a difference? ... I've already cleaned tank and replaced sending unit, replaced gas cap with a vented version and insulated metal fuel line from pump to carb
 

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I'm having issues with my fuel delivery on my all original 56 Bel Air with the 256 motor ... with a warm motor I'm seeing what appears to be fuel flashing or vaporizing in the fuel line downstream of the fuel pump, gas percolates and l loose level in the glass filter just upstream of carb ... I've replaced the fuel pump with a like and kind replacement 50gph 5.5psi pump ... would a higher psi/gph pump make a difference? ... I've already cleaned tank and replaced sending unit, replaced gas cap with a vented version and insulated metal fuel line from pump to carb
how close is the fuel line to the exhaust?? Someone chime in and correct me if I'm wrong but I think you're a little over kill on fuel pump for stock 265
 

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Do not replace the pump with one with higher PSI output. It will cause problems with your carbs fuel inlet needle and seat. You may be experiencing what many others and I myself have had to deal with lately. And that is the poor quality of the currently available Chinese manufactured fuel pumps. They are JUNK! Here is a link to my fuel pump thread. I had the same symptoms with two brand new pumps. It doesn't matter what brand you buy, the problem is that they are all built in the same Chinese factory. I finally resorted to buying an original AC fuel pump and rebuilding it. Problem solved!

Steve
 

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A glass fuel filter will not fill all the way to the top, so the fuel will appear to bubble and slosh inside the glass bowl. This is normal.

If your car is running well, leave it alone.

Forgot to mention: are you running ethanol-free gasoline? That's all I use, and for good reason.
 

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Also, you're not hurting anything by having a 50 gph fuel pump, but it's overkill. With a 16 gallon gas tank, that pump running at full output would drain the tank in roughly 20 minutes. I doubt you could push that much fuel through a 283 even under racing conditions. As long as the pump can keep up under full throttle, it's big enough.

A fuel pump will only pump fuel when the fuel level in the carb bowl drops, which causes the float to drop, which opens the needle and seat. Otherwise, it just sits there, waiting for the call to provide more fuel. Hence, the flow of fuel into the filter will be intermittent, especially at idle.

All of this works very much the same as the tank on the back of your toilet - it fills as needed, then the supply line sits there at pressure, waiting for the call to top off the level again..

As Steve mentioned, fuel pump pressure is VERY important. You don't want to go to a higher PSI. The carburetor float is designed to work with a pump with a specified pressure; if you go higher, the pump will overfill the carburetor.
 

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🐔County, TN. 55 Bel Air Sport Coupe
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I'd guess the fuel is getting too hot. Either like said, the line too close to the exhaust, or the heat being picked up by the fuel pump mounted on the engine. Get it hot so it's percolating, then take a garden hose and run cold water onto the pump (it takes a while) to see if it goes away. My clear temporary filter for this test would get so low that I was surprised that it still ran! After cooling off the pump, the filter filled most of the way again. The only time it actually affected my engine was when winding out the gears at full throttle. Otherwise it was OK to drive. I tried nearly every trick in the book and then a dozen more and the only thing that worked is installing a remote electric fuel pump and capping off the hole for the mechanical pump. I had previously run a return line back to the tank to keep the fuel moving and that is still in place, so I really don't know if you (or I) need the bypass.
On the other hand, if you don't like the idea of an electric fuel pump, go ahead and run a regulator with a bypass for the return top the tank to see if the fuel keep moving fast enough to solve your problem, that is if you have an actual problem, or just an observation.
 

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Since we're on the subject of vapor lock, allow me to discuss/rant for a moment.

My '57 has a 283 with a stock Carter WCFB and factory dual exhaust. I have NEVER had a problem with vapor lock. I've not even had a problem in the 95 degree weather we've been having of late (yes, I've been driving it around in 95 degree weather and no A/C).

Let me share with you why I think that's the case.

First, I use nothing but ethanol free gas in it. E10 in my fuel injected daily drivers, but only E0 in the '57.

Modern fuels can run with higher volatility in the mix and run just fine in any car built in the last 30+ years. These cars have a closed fuel delivery system with a return line to the tank, so fuel is constantly circulating. It's also under about 50 PSI instead of 5 PSI, which reduces vaporization. But, the higher volatility can be a bit problematic with a vented gas cap, no return line, and a 5 PSI fuel pump.

A lot of guys put dual exhausts on a car originally equipped with single exhaust without rerouting their fuel and brake lines to the outside of the frame. Then, they wonder why they have vapor lock. Umm...there's a reason GM spent the extra money on dual-exhaust-equipped cars (extra cost for more material and a little more work to install the line) to run the fuel and brake lines on the outside of the frame.

If you're running a 195 degree thermostat instead of 180 degree, your engine is, well, hotter. Heat causes fuel vaporization. Hmm....

If the fuel line is properly routed away from the exhaust, fuel shouldn't be vaporizing in the long fuel line before getting near the engine. It might vaporize at the fuel pump, or in the line going up to the carb.

If you're running any of the stock carbs, vaporization in the line going to the carb is no big deal. The fuel will bubble and all that, but the vapors will simply go out the external bowl vent, and liquid fuel will start flowing momentarily. These vents are always open on a stock 1 or 2 bbl carb. The WCFB vent is only open at idle, so make sure the arm that opens the vent is adjusted to spec. The 4GC has very tiny vent holes near the air cleaner - make sure they're clear, as they're none too big to start with.

If you're running a later-year or aftermarket carb, you need to check how the bowl is externally vented. Carbs from the 1960s are typically vented like the WCFB, so that adjustment is critical.

I recently looked at a carb for a guy with a 1960s Mustang but using an emissions controlled 1970s carb. There was a bowl vent that was supposed to connect to a charcoal canister via rubber hose. He had put a cap on the vent. I told him to take the cap off, and the car would run correctly.

Similarly, you need to check how your Holley or Edelbrock's bowl is vented.
 

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Discussion Starter · #8 ·
Do not replace the pump with one with higher PSI output. It will cause problems with your carbs fuel inlet needle and seat. You may be experiencing what many others and I myself have had to deal with lately. And that is the poor quality of the currently available Chinese manufactured fuel pumps. They are JUNK! Here is a link to my fuel pump thread. I had the same symptoms with two brand new pumps. It doesn't matter what brand you buy, the problem is that they are all built in the same Chinese factory. I finally resorted to buying an original AC fuel pump and rebuilding it. Problem solved!

Steve
Thanks Steve ... I just found and ordered a rebuilt NOS AC 4460 Fuel pump on ebay ... thanks for the link
 

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Discussion Starter · #9 ·
A glass fuel filter will not fill all the way to the top, so the fuel will appear to bubble and slosh inside the glass bowl. This is normal.

If your car is running well, leave it alone.

Forgot to mention: are you running ethanol-free gasoline? That's all I use, and for good reason.
unfortunately the closest ethonal free gas station is over 50 miles away
 

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🐔County, TN. 55 Bel Air Sport Coupe
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Ethanol has a boiling point of about 173°F.
Butane boils at 32°F
Winter gas, depending on your location, can boil at as low as 100°F. The low boiling point is primarily due to adding more Butane into it.
Summer gas has less butane in it and boils at a higher temp than winter gas (I don't know the actual number). Ethanol raises the boiling point of gas, and helps prevent vapor lock.
E-10 seems to work quite well with vehicles that are driven often, sorry but I don't know HOW often? If a vehicle sits for longer periods of time, E-10 is bad for it due to various reasons.
All of this info is the long way of saying "E-10 doesn't cause vapor lock" , "but it is trouble if the vehicle isn't driven often".
 

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My experience with E10 has not been good with carbureted engines. I had carburetor damage on small engines (my nearly 30 year old riding mower in particular) that hasn't reoccurred since switching back to nothing but E0. There was a noticeable - and immediate - difference in performance in my '57 (283 with a WCFB) when I switched to E0. Whether E10 does or doesn't contribute to vapor lock is beside the point for me with these engines.

The retired Rochester engineer in our car club told of participating in fuel volatility vs. engine cold start tests around 1970. All the major oil companies and car manufacturers participated in the testing. More volatile won every time.

With the sealed fuel systems used in all vehicles built in the past 30+ years, higher volatility is less of an evaporation issue, all while facilitating more complete combustion, thereby lowering emissions. Now, I'm not a petroleum engineer, so I can't tell you with authority how fuel formulation has evolved since the 1950s. But, I'm guessing our fuels today are in general more volatile than in decades gone by.
 

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Discussion Starter · #12 ·
Ethanol has a boiling point of about 173°F.
Butane boils at 32°F
Winter gas, depending on your location, can boil at as low as 100°F. The low boiling point is primarily due to adding more Butane into it.
Summer gas has less butane in it and boils at a higher temp than winter gas (I don't know the actual number). Ethanol raises the boiling point of gas, and helps prevent vapor lock.
E-10 seems to work quite well with vehicles that are driven often, sorry but I don't know HOW often? If a vehicle sits for longer periods of time, E-10 is bad for it due to various reasons.
All of this info is the long way of saying "E-10 doesn't cause vapor lock" , "but it is trouble if the vehicle isn't driven often".
Ethanol has a boiling point of about 173°F.
Butane boils at 32°F
Winter gas, depending on your location, can boil at as low as 100°F. The low boiling point is primarily due to adding more Butane into it.
Summer gas has less butane in it and boils at a higher temp than winter gas (I don't know the actual number). Ethanol raises the boiling point of gas, and helps prevent vapor lock.
E-10 seems to work quite well with vehicles that are driven often, sorry but I don't know HOW often? If a vehicle sits for longer periods of time, E-10 is bad for it due to various reasons.
All of this info is the long way of saying "E-10 doesn't cause vapor lock" , "but it is trouble if the vehicle isn't driven often".
thanks for the info … may biggest take away from this is if I’m having trouble now while on the summer blend gasoline it may only get worse on the winter blend 🤦🏽‍♂️
 

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Discussion Starter · #13 ·
My experience with E10 has not been good with carbureted engines. I had carburetor damage on small engines (my nearly 30 year old riding mower in particular) that hasn't reoccurred since switching back to nothing but E0. There was a noticeable - and immediate - difference in performance in my '57 (283 with a WCFB) when I switched to E0. Whether E10 does or doesn't contribute to vapor lock is beside the point for me with these engines.

The retired Rochester engineer in our car club told of participating in fuel volatility vs. engine cold start tests around 1970. All the major oil companies and car manufacturers participated in the testing. More volatile won every time.

With the sealed fuel systems used in all vehicles built in the past 30+ years, higher volatility is less of an evaporation issue, all while facilitating more complete combustion, thereby lowering emissions. Now, I'm not a petroleum engineer, so I can't tell you with authority how fuel formulation has evolved since the 1950s. But, I'm guessing our fuels today are in general more volatile than in decades gone by.
So much conflicting information from so many experienced people only adds to my frustrations and makes troubleshooting that more difficult … but I’ll stay at it
 

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thanks for the info … may biggest take away from this is if I’m having trouble now while on the summer blend gasoline it may only get worse on the winter blend 🤦🏽‍♂️
With cooler winter temps the gas doesn't boil as easy. The worst time is if you have winter gas and happen to have a really warm spring day.
 

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With cooler winter temps the gas doesn't boil as easy. The worst time is if you have winter gas and happen to have a really warm spring day.
The fuel volatility tests the Rochester engineer described show why volatility is important in winter gasoline.

Picture a group of brand-new 1970 model cars from every major manufacturer sitting in a row. Picture engineers from the car companies and oil companies, sitting...waiting....

It's early morning at the test site. Everyone is patiently waiting for the temperature to hit exactly 36 degrees.

When that happens, the instructions are simple: Start the car. Wait 10 seconds. Put it in Drive, and floor it.

Does the car take off? Does it stumble while taking off? Does it backfire and stall?

They tested 3 levels of volatility over the days of testing. The most volatile gas did the best across all cars and fuel vendors.

Of course - picture that same volatility fuel when the temperature is above 90 degrees...
 

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That's very interesting. Most resources only tell you that in the winter they use more butane because it's cheap and plentiful. Which it is, but they don't tell you "the rest of the story" as Paul Harvey would have said. They do tell us that more butane is the reason winter gas is normally cheaper than summer gas.
Will more volatile gasoline will give you more HP not just cold, but when the motor is warmed up also? Is "race gas" more volatile?
 

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Discussion Starter · #17 ·
I'd guess the fuel is getting too hot. Either like said, the line too close to the exhaust, or the heat being picked up by the fuel pump mounted on the engine. Get it hot so it's percolating, then take a garden hose and run cold water onto the pump (it takes a while) to see if it goes away. My clear temporary filter for this test would get so low that I was surprised that it still ran! After cooling off the pump, the filter filled most of the way again. The only time it actually affected my engine was when winding out the gears at full throttle. Otherwise it was OK to drive. I tried nearly every trick in the book and then a dozen more and the only thing that worked is installing a remote electric fuel pump and capping off the hole for the mechanical pump. I had previously run a return line back to the tank to keep the fuel moving and that is still in place, so I really don't know if you (or I) need the bypass.
On the other hand, if you don't like the idea of an electric fuel pump, go ahead and run a regulator with a bypass for the return top the tank to see if the fuel keep moving fast enough to solve your problem, that is if you have an actual problem, or just an observation.
I found a NOS fuel pump on EBay so I’ll try that … if that doesn’t work I’ll switch to an electric pump
 

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Discussion Starter · #18 ·
The fuel volatility tests the Rochester engineer described show why volatility is important in winter gasoline.

Picture a group of brand-new 1970 model cars from every major manufacturer sitting in a row. Picture engineers from the car companies and oil companies, sitting...waiting....

It's early morning at the test site. Everyone is patiently waiting for the temperature to hit exactly 36 degrees.

When that happens, the instructions are simple: Start the car. Wait 10 seconds. Put it in Drive, and floor it.

Does the car take off? Does it stumble while taking off? Does it backfire and stall?

They tested 3 levels of volatility over the days of testing. The most volatile gas did the best across all cars and fuel vendors.

Of course - picture that same volatility fuel when the temperature is above 90 degrees...
My car has no issues at start up and my drive time varies from 20 to 40 minutes before it stalls. I drove to a local show yesterday roughly 10 minutes from my house. Got there with no issues, car drove fine and strong. Stayed at the show for about 3 hours. On my way home 6 minutes into my ride it began to stumble and eventually stalled. I am able to restart and limp it home. No backfires no stumble at startup. The inconsistency and unpredictablity is what’s most annoying
 

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Discussion Starter · #19 ·
My car has no issues at start up and my drive time varies from 20 to 40 minutes before it stalls. I drove to a local show yesterday roughly 10 minutes from my house. Got there with no issues, car drove fine and strong. Stayed at the show for about 3 hours. On my way home 6 minutes into my ride it began to stumble and eventually stalled. I am able to restart and limp it home. No backfires no stumble at startup. The inconsistency and unpredictablity is what’s most annoying
Let me add the weather was mild in the 80’s and car thermostat never showed high 🤷🏽‍♂️
 

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I'm having issues with my fuel delivery on my all original 56 Bel Air with the 256 motor ... with a warm motor I'm seeing what appears to be fuel flashing or vaporizing in the fuel line
I had that symptom and discovered that the rubber hose from the tank to the hard line was old and cracked which allowed the mechanical pump to suck air into the fuel line and consequently reduced the pump performance.
 
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