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Thread: BB 454 Fuel Pump

  1. #11
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    Quote Originally Posted by chevynut View Post
    Is this a new problem, and did the car run fine at 90+ MPH before?

    What "return line" are you referring to? Are you running a regulator? Holley says you don't need a regulator with that pump. Also, you said you have a 3/8" line "from the pickup"....is the pickup itself a 3/8" one inside the tank?

    I had a 55 Chevy with a '67 Corvette 390 HP 427 in it and it would starve for fuel at high RPM....similar to what you're describing. I used the stock mechanical fuel pump with the stock 5/16" line and I'm pretty sure the line was the problem. It needs to be clear all the way to the pump with no restrictions. Make sure you don't have any restrictive fittings in the lines.
    I believe it is a new problem. But it did happen on a warm day with winter gas, just not as bad as before. The pickup is 3/8. I don't know what it is here, no one else in other area's has fuel that boils so easy.
    Tony

    1955 Bel Air Sport Coupe

  2. #12
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    Quote Originally Posted by 55 Tony View Post
    The old "running out of gas" problem has always, always, always happened when the temperature was high. It became *practically* non existent when I installed a filter with a bypass as close to the carb as possible.
    The boiling over at first happened while driving when the ambient temp was very high, then after adding the spacer and blocking the crossovers it stopped with the quadrajet but still did it at times with the holley after it was turned off, I believe only from the secondary bowl.

    There is a permanent gauge on the regulator, so no I can not monitor it while driving. Do people run them inside like a oil pressure gauge?
    Running a fuel pressure gauge would be a good idea, but not inside the car unless you have an pressure isolator, or an electric sender.

  3. #13
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    Quote Originally Posted by 55 Rescue Dog View Post
    Running a fuel pressure gauge would be a good idea, but not inside the car unless you have an pressure isolator, or an electric sender.
    I'll have to look at Summit. Never saw either one of those, that's why the gauge is under the hood!
    Tony

    1955 Bel Air Sport Coupe

  4. #14
    Registered Member chevynut's Avatar
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    I agree with Rick, your fuel isn't going to boil at WOT and that's not your problem. I would at least temporarily plumb a fuel pressure gauge into the car so you can watch it and see if the pressure drops off when the engine loses power. Personally I wouldn't worry about plumbing a temporary fuel line into the car using the appropriate fittings and a rubber fuel line for troubleshooting. You're not running high pressure so the safety risk is low. For a permanent installation I'd use an electric fuel pressure sender and gauge. If the pressure drops off when the engine starts to die at high RPM, I'll bet you either have a bad pump or a restriction in the line between the pump and tank. If it was me I'd be using an electric pump at the rear of the car and ditch the mechanical one. It's better to push fuel than to suck it.
    56 Nomad, Ramjet 502, Viper 6-speed T56, C4 Corvette front and rear suspension


    Other vehicles:

    56 Chevy 2-door BelAir sedan
    56 Chevy 210 4-door sedan
    57 Chevy 210 4-door sedan
    1962 327/340HP Corvette
    1961 Willys CJ3B Jeep
    2001 Porsche Boxster S
    2003 Chevy Silverado 2500 HD Duramax
    2019 GMC Sierra Denali Duramax

  5. #15
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    I believe the only time pushing fuel is easier than pulling it, is when the line has air in it. Once primed the mechanical pumps work just fine.
    I might hook up a temporary gauge like you say, if I can find the right fittings. I think I may tape it to the outside of the windshield. Then wait a day or two till the rain stops.
    Tony

    1955 Bel Air Sport Coupe

  6. #16
    Registered Member chevynut's Avatar
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    I still don't understand what "return line" you're referring to and what the "filter with a bypass" that you mentioned is.

    With a mechanical pump you will ALWAYS have suction in the supply line between the pump and the tank. If you pull enough of a suction on the fuel line, due to a high volume pump and a restrictive line between the pump and the tank, you can cause vapor lock in the fuel line under the right conditions. For example, if the pump is trying to supply the carb at the 38 GPH you're burning it (at 450 HP) but it's pumping at full capacity and the regulator is bypassing the remainder of the 110 GPH of fuel pumping capacity back to the tank, the supply line may not be able to supply enough fuel and the pump is pulling a vacuum on the line. If it pulls enough of a vacuum, it can cause vapor lock or at least a drop in fuel pressure.

    "Vapor lock was far more common in older gasoline fuel systems incorporating a low-pressure mechanical fuel pump driven by the engine, located in the engine compartment and feeding a carburetor. Such pumps were typically located higher than the fuel tank, were directly heated by the engine and fed fuel directly to the float bowl inside the carburetor. Fuel was drawn under negative pressure (gauge pressure) from the feed line, increasing the risk of a vapor lock developing between the tank and pump. A vapor lock being drawn into the fuel pump could disrupt the fuel pressure long enough for the float chamber in the carburetor to partially or completely drain, causing fuel starvation in the engine. Even temporary disruption of fuel supply into the float chamber is not ideal; most carburetors are designed to run at a fixed level of fuel in the float bowl and reducing the level will reduce the fuel to air mixture delivered to the engine."

    Here's some info on fuel line sizing. http://fuelab.com/fuel-line-size-vs-pressure-drop/

    You mentioned a return line before so I believe you must have a regulator plumbed in. Since the Holley pump doesn't need a regulator (according to Holley) I would remove it so it doesn't bypass fuel back to the tank. That just makes the pump work harder, pulling more fuel through the fuel supply line.

    http://documents.holley.com/fuel_pump_tech_info.pdf

    "110 GPH pumps are designed for street/strip applications where substantially higher than stock fuel delivery requirements are necessary. 3/8" inlet and outlet ports are utilized and, with fuel shut-off pressure in the area of 6-1/2 - 8 PSI, a regulator is not required."

    So if your regulator is set at 5 psi you're always bypassing fuel to the tank making the pump draw more fuel through the supply line.

    56 Nomad, Ramjet 502, Viper 6-speed T56, C4 Corvette front and rear suspension


    Other vehicles:

    56 Chevy 2-door BelAir sedan
    56 Chevy 210 4-door sedan
    57 Chevy 210 4-door sedan
    1962 327/340HP Corvette
    1961 Willys CJ3B Jeep
    2001 Porsche Boxster S
    2003 Chevy Silverado 2500 HD Duramax
    2019 GMC Sierra Denali Duramax

  7. #17
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    https://www.autozone.com/filters-and...ter/830813_0_0
    When I installed the above filter and ran a return line back to the tank, the "running out of gas" symptoms that were common in summer temps above 80F disappeared but did return not as bad in temps above 90F. The filter is made so if there is any vapor, it floats up to the return part of the filter. The outlet to the carb is down lower so it gets liquid. This filter has to be installed in at least partially upright position with the bypass at the top to function properly.

    Now I will say again, after running the return line, the vapor problem got much, much better, not worse. The filter above is plumbed in about 1.5" before the carb to minimize the area for more vapor to form before getting to the carb.
    Tony

    1955 Bel Air Sport Coupe

  8. #18
    Registered Member chevynut's Avatar
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    Quote Originally Posted by 55 Tony View Post
    https://www.autozone.com/filters-and...ter/830813_0_0
    When I installed the above filter and ran a return line back to the tank, the "running out of gas" symptoms that were common in summer temps above 80F disappeared but did return not as bad in temps above 90F. The filter is made so if there is any vapor, it floats up to the return part of the filter. The outlet to the carb is down lower so it gets liquid. This filter has to be installed in at least partially upright position with the bypass at the top to function properly.

    Now I will say again, after running the return line, the vapor problem got much, much better, not worse. The filter above is plumbed in about 1.5" before the carb to minimize the area for more vapor to form before getting to the carb.
    Are you talking about two different problems? You've mentioned a "running out of gas" problem and a "vapor" problem. Sounds like one is at high speed/RPM and the other is at idle.

    So you don't have a pressure regulator, and the "return" you're talking about is only the filter vent line and the filter has a constant flow of fuel returning to the tank?

    Vapor lock is more likely to show up BEFORE the pump unless the line past the pump gets hot. After the pump the gas is under pressure and at the same temperature, the gas on the suction side of the pump will vaporize before the gas on the pressure side. The faster the engine is turning the more suction you get on the fuel line. The more suction, the more chance of vapor lock. The constant flow of gas back to the tank forces the pump to pump harder, creating more suction. If the fuel line is close to the exhaust, it will get hot and make the problem worse.

    I don't see how the return line helps at high RPM at 90 MPH. I'd plug the return line and take it out again at high speed to see if it changes the problem. If not, I still say you have a restriction somewhere in the fuel line, if the pump is working properly. Or the fuel line ahead of the pump is getting hot.

    http://www.camaros.net/forums/33-cam...apor-lock.html
    56 Nomad, Ramjet 502, Viper 6-speed T56, C4 Corvette front and rear suspension


    Other vehicles:

    56 Chevy 2-door BelAir sedan
    56 Chevy 210 4-door sedan
    57 Chevy 210 4-door sedan
    1962 327/340HP Corvette
    1961 Willys CJ3B Jeep
    2001 Porsche Boxster S
    2003 Chevy Silverado 2500 HD Duramax
    2019 GMC Sierra Denali Duramax

  9. #19
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    No both were at high rpm. Only problem I ever had at idle was fuel boiling over in the carb and stalling and flooding the engine. Basically I believe the constant flow of fuel normally keeps it from getting hot and vapor locking. From everything I've been through I believe that to be true. Maybe a pump back at the tank will help? I'm curious if anyone installed a vacuum gauge in the fuel line back at the tank to see how much vacuum there actually is. I did have the 3/8 line before the bypass and adding the bypass made the problem pretty much go away until now, and a few times when it was very hot. I'll go out and install the new pressure gauge I got and put it on the windshield and with any luck I'll be able to test it tomorrow with and without the bypass. Have to wait for dry roads.

    Oops, got that wrong. If someone was to install a vacuum gauge on the fuel line, it would go directly before the pump, not back at the tank.
    Last edited by 55 Tony; 01-28-2018 at 03:27 PM.
    Tony

    1955 Bel Air Sport Coupe

  10. #20
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    Quote Originally Posted by 55 Tony View Post
    No both were at high rpm. Only problem I ever had at idle was fuel boiling over in the carb and stalling and flooding the engine. Basically I believe the constant flow of fuel normally keeps it from getting hot and vapor locking. From everything I've been through I believe that to be true. Maybe a pump back at the tank will help? I'm curious if anyone installed a vacuum gauge in the fuel line back at the tank to see how much vacuum there actually is. I did have the 3/8 line before the bypass and adding the bypass made the problem pretty much go away until now, and a few times when it was very hot. I'll go out and install the new pressure gauge I got and put it on the windshield and with any luck I'll be able to test it tomorrow with and without the bypass. Have to wait for dry roads.
    Try to attach your gauge near the fuel inlet to the carb, or after the filter.

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