How much pressure should electric pumps be putting out? I was getting fed-up with my dual tank in-tank pumps and have bought 2 electric (Rail-mount pumps) each capable of pushing 5-7 PSI. I have an 84 F250 w/460 and a new Holley Street Avenger 670 cfm Carb. I also just got rid of all my old fuel lines (metal and rubber) and replaced the fuel supply line with 3/8 fuel line, and the return line with 7/16 fuel line. I put an in line filter in each line right after it exits the tank. My external pump was working okay, (I only drove it once), but when I hooked up the front tank again, (just the lines, I haven't put the other external pump on yet) now it runs fine on the front tank, but dies immediately on the rear... I think my wiring to my switch valve is faulty, I found one broke, I got no gas at all, I fixed it but now I don't seem to get gas from the rear. I am about to rebuild the fuel harness so the witing isn't so old and crappy. But I still want to be sure 5-7 pounds is adequate. The truck ran pretty giid until I put the new Carb on (Street Avenger 670) then started dying at high RPM 55+MPH. Drop down to 35-40 and it was okay. But I can rev the engine up sitting still and it didn't die, possibly EGR? I need some advice, I love this truck and have restored most of it and redone all the wiring, this fuel thing is really starting to **&%$% off!

 

5-7psi is plenty. Have you checked actual pressure while driving? If it ran fine before changing carbs, I would double check the float levels, they could be low.

 

Roger that, I have adjusted the floats once already. Tonight I went out and fired it up and it ran but really rough. I haven't been driving it much lately but that shouldn't be a reason for the rough running???? I think I may have a vaccum leak somehwere, so I'll check that as well. My external pump is on the driver side rail below the level of the tank about 8-10 inches in front of it, I have read that positioning of the pump can affect the running as well. Thanks for the advice.

 

Sounds like the pump is properly. It should get a good gravity feed there so I would doubt that you have a problem there. I don't know if having a filter before the pump may be too restrictive.

 

Most fuel pumps are more pusher than suckers. They can push the fuel to the carb better than they can suck through a restricted line/filter.

 

Dying at upper RPM's? I have the same situation with my current setup on my mudder. I hammer it, and it start acting like it's only running on 4 cylinders. I adjusted my timing, and have yet to test it again, but I think that may be the culprit. I know it's got good fuel pressure, and the carb is good, cuz when I rev it halfway sitting still, then hammer it, I can hear the secondaries opening. If the timing is too far advanced, the extra fuel doesn't get burned and jsut exits the pipe and causes the engine to stall. What are your RPM's at 55+? If you're higher in the RPM range, the secondaries may be opening and advancing the timing, thus the stall. In all honesty, a 670 CFM carb isn't the BEST choice for a big block, (750 or 850 preferable), but I'm running a 650 myself, so I can't knock you too bad. May want to check your timing or recurve the advance, or just retard the timing a bit. I'm curious to hear other responses.

 

I had this problem on my highboy and it turned out to be a bad vacuum advance. Switched it and have not had anymore problems.

 

Thanks for the information, this is my project truck, and now that my wife has her own car, (I can drive my 2004 GMC) I am going back over the whole system from rear to front. I have replaced all the old metal lines with Black fuel line 3/8'' for supply, and 7/16 for return. I have my rear pump moved to external and just need to do the same with the front now. I took off the body wiring harness so I can clean it up and fix the switch valve connection, and I replaced the Distributor Cap & Rotor. When I put it all back together I'll try the Vaccum advance, and reset the timing. Thanks for the help. If I didn't love this truck I'd have called it quits long ago...