starving for gas

[runamuck]

thought I had a vapor lock problem 63 c20 4x4 on early 70's blazer frame w/327ci bowtie. installed new fuel pump, still runs maybe 15-20 miles and then starves for gas, then installed new red holly electric pump, new canister filter before pump, and a pressure gauge right after a see thru filter near carb, 4 1/2 lbs fuel pressure at carb, then ran for 15-20 miles and same problem, no fuel pressure and see thru filter empty. I see the fuel line coming out of behind seat gas tank is on top? How does this work, is the pickup inside fed by siphon? Seems to me if it's gravity fed to pump, fuel line would come out the bottom of tank, oh yes, I installed the holly pump right under the tank. plus, seeing how it's not the fuel pump, can I run the mechanical pump, with the holly electric still inline, but turned off? (holly is kinda loud)

[J kippin]

check the fuel line routing, it seems like you may be getting vapor lock. Make sure fuel line isn't close to exhaust or engine components. Fuel pump should have enough suction to pull fuel from the tank it is not a gravity feed. You may want to sending unit from the tank and check the sock on the end of the pick-up crud if the tank is old.

[J kippin]

I would suggest to remove the Holley pump and pre-filter before the pump. Mechanical pump probably will not pull fuel through those items.

[runamuck]

Originally Posted by J kippin

check the fuel line routing, it seems like you may be getting vapor lock. Make sure fuel line isn't close to exhaust or engine components. Fuel pump should have enough suction to pull fuel from the tank it is not a gravity feed. You may want to sending unit from the tank and check the sock on the end of the pick-up crud if the tank is old.

thanks for the info, I just removed the tank sending unit and it's a little rusty at the pick up sock, and the line is rusty inside, I think I'll replace the whole unit and then remove and Replace the fuel line and move it away from the headers, at one point the line is maybe 3" from the exhaust header. Hey kippin, do you think I can then run my new mechanical fuel pump without having to remove the electric pump? I can turn the electric pump off at the dash if I want?

[runamuck]

Originally Posted by J kippin

I would suggest to remove the Holley pump and pre-filter before the pump. Mechanical pump probably will not pull fuel through those items.

oh, ok, so you suggest removing the canister filter that is installed just below the gas tank, and before the mech. pump, and not route the gas line thru the electric pump if I'm using the mechanical pump,right?

[J kippin]

I would remove the filter and pump because it may not be a regular service item for you. I also don't know what the flow rates is threw your filter. I stock pump doesn't like to suck fuel real well with a lot of restrictions. Electric pumps push fuel real well that is why the manufacturers recommend putting the pumps close to the tank and use a pre-filter to protect the pump.
the stock pump should provide adequate fuel. Only other option I would pursue would be to remove the mechanical pump and just use the electric. Even mounted with the supplied rubber biscuits they are still loud. I use to run two Holley blue pumps on my 72 Z28 with a BBC The dual Flow masters helped cancel out their noise.

[runamuck]

Originally Posted by J kippin

I would remove the filter and pump because it may not be a regular service item for you. I also don't know what the flow rates is threw your filter. I stock pump doesn't like to suck fuel real well with a lot of restrictions. Electric pumps push fuel real well that is why the manufacturers recommend putting the pumps close to the tank and use a pre-filter to protect the pump.
the stock pump should provide adequate fuel. Only other option I would pursue would be to remove the mechanical pump and just use the electric. Even mounted with the supplied rubber biscuits they are still loud. I use to run two Holley blue pumps on my 72 Z28 with a BBC The dual Flow masters helped cancel out their noise.

thanks, I think I'll stick with the holly electric seeing how I already have it installed on the frame right under the tank with the canister filter fefore the pump, and have the mechinical pump off and a plate over the hole. I did mount the pump on a piece of soft wood with rubber bushings, then mounted the piece of wood to the frame with rubber dampers, so I really can't hear it once the engine is started, plus I have it wired through a relay and through the ignition switch so it turns off when the key is off, and also I have it on a switch if I want to have the key on for some reason but not run the engine. I hope when I install new sending unit, and fuel lines away from heat source it cures the problem, as I said, it has to be a problem between the see thru fuel filter I have right before the pressure gauge and carb, because when it happend the see thru is mt, and there is no pressure, and if you let it sit, it will run again for a while.

[J kippin]

just one last thing I would check is the vents for the fuel tank/or cap. If it is not properly vented it my give you problems. what pump are you using? are you using a pressure regulator? Pump pressures will vary with temperature. Too much pressure and you will have float problems. I like to keep pressure set around 5-6 psi

[runamuck]

Originally Posted by J kippin

just one last thing I would check is the vents for the fuel tank/or cap. If it is not properly vented it my give you problems. what pump are you using? are you using a pressure regulator? Pump pressures will vary with temperature. Too much pressure and you will have float problems. I like to keep pressure set around 5-6 psi

Thanks for all the great advice, I'm not using a regulator, the Holly Red pump doesn't need one, I'm running between 4 1/2 and 5 1/2 lbs. pressure at the carb. I tried to run with the gas cap off and it didn't make any difference, next weekend I'm gonna replace the sending unit inside the tank with a new "filter sock" and replace and move the wgole fuel line from the tank to the carb, I'm hoping that does it. Again, thanks for your insight.