I might be beating a dead horse, but i cant figure this out. I have a &! dodge dart with a new (450 miles new) 340 .20 over, RPM Aluminum heads and and pistons. i cant remember the exact cam except its a crane, and a mighty demon 750 carb. Ok so I have gas in the tank and 3/8" lines from the tank to the old stock steel lines that run along the car up to the engine bay. Then back to 3/8" line to the mechanical fuel pump and up to the carb.

OK so when i start the car fuel pressure is like 4.5 - 5.5. and as the car runs for a bit it just falls to like 2-3. Now if i drive it around the block then stop and check 0-1. Im afraid to go out of the neighborhood due to the fact that it will die like its out of gas. Then after pumping and pumping the gas and cranking the engine over. it will finally start and idle fine but then when i drive again dead. Its almost as if my fuel pump cant keep up with the demand of the carb/motor. (the fuel pump is a basic carter 5.5-6.5 psi max). Im going nuts here. Sorry for the long thread. Thanks.

Landon from Hawaii.

 

Is the fuel pump new?

It sounds like the pump isn't keeping up. I think that the fuel pump arm, on a 340, rides on a cam lobe. Maybe the arm needs to be adjusted or somehow got bent and isn't getting the full push from the cam to make the pump do what it's supposed to do.

On my boat, I have a Holley mechanical fuel pump with a fuel pressure gauge plumbed inline to my Holley 850 and it stays pretty constant.

 

Check the sock in the gas tank and fuel filter. If you tank is old you may have one or both collecting crud.

 

Be sure any hoses you have for connections on the suction side of the pump are not collapsing, and are rated for fuel use.

As above, check the tank pickup, AND ALSO be sure the tank is being vented. Easy way to do that is to run it without the cap

Buy a vacuum/ pressure gauge at any parts store, and check pump suction in this case both at the tank and at the pump

Suspect pinholes or obstructions (rust, debri) in the old tubing (I assume it is old/ original?)

 

I am going to pull the tank and put in a new sending unit. One issue is that when i connect a hose to the fuel pump side and then directly into a gas can eliminating the whole fuel line. I still only have about 3-4 psi. Could my carb/ motor be pulling more fuel than the pump can supply. by the way there is no change in pressure if i rev the engine. Should i just stop messing around and get an electrical fuel pump or and better mechanical one.

 

How tight are the 3/8 hose to the steel line connections? If your original lines are 5/16 that 3/8 hose will fit kind of loose on it. It may not leak fuel but it may be sucking air. If your using the typical braided fuel line try a better grade. I've been using a Goodyear brand that is rated for use on fuel injection systems. A good mechanical pump may be needed but be more concerned about GPM than PSI. Hope this helps.

 

thanks for the info guys. So Im going to replace all the lines along with the sending unit. what do you recommend as for a pump.(mechanical). and what is the difference between gph and psi. Someone told me that my Mighty demon should have about 6-8 psi fuel pressure. But I don't know.

 

This is similar to the pump that I run on the BBC in my ski boat, and has been trouble free.

http://www.holley.com/12-360-11.asp

 

On my 1940 ford pickup I restored not too long ago I had a similar problem. The truck had a 350 in it and an electronic fuel pump. I put an inline filter just before the pump. I made the HUGE mistake of using the tank the truck had in it. The had been restored about 20 years before I got it. But it had sat in a field for a long while. Any how long story short I tried cleaning the tank out. First time to run it I got about 2 miles and it lost fuel pressure and died. Let it set a couple minutes, it started up no problem and I got about another 500 yards and died again. Changed the filter got about 5 miles before it happened again. Anyhow I ended up putting a new tank in it never had a problem with the fuel system again. So if you used the original tank I would do like the guys said on here before and change out the sock on the sending unit. Or just change the tank. But If I were you I would just change the tank and sending unit. Your lines are probably fine just take a little bit of gas and blow through them with an air hose. keep doin it til it starts comin out clean on the other end. That will save you a lot of time and hell with those metal lines. Hope this helps.... And btw I used the original fuel lines on my 40, done exactly what I just said and after I changed the tank didn't have a problem.

 

GPH is the amount of fuel that is flowing. PSI is the amount of pressure that is pushing that fuel

 

After you get your fuel problem fixed, let us know what it was. I would like to see more pics of that car. That first picture sure looked good. What island are you on?

 

Ok some of you asked for more pics. So here you go. And on a better note.... new sending unit, all new lines with a carter super street pump were cookin now. I am most likely going to sell this car and would love some advise on what you guys truly think i can get for it. I know all the mopar guys like cuda's and chargers but i don't want to give it away but also don't want to rip anyone off.

Its a 340 .20 over with RPM performer heads and Pistons. everything port and polished mighty demon 750 carb new everything from alternator to fuel lines. Has a 904 3 speed trans with a ford 8 1/4 rear end and 3.08 gears. then interior is all new from the seats to the carpet. No tears cracks or anything. the only thing wrong is the speedo doesn't kick in until 20mph. Here are some pics and a video link to youtube.













Video link http://www.youtube.com/watch?v=jVOivoEzDno

 

That's a nice car but I have to tell you it might take a "special someone" to like the paint combo.

 

There is a check valve in the vent coming from the fuel tank that connects to a rubber line on the passenger side in the front on the radiator support remove rubber line from steel vent line cut the last inch off the steel vent line where it connects to rubber line recconect rubber line problem solved the check valve is pressed into that last inch of line the tank will now vent

 

Easier way would be to take the gas cap off and try it.. I would suspect the rubber lines at the top of the tank where it connects to the sending unit. That is what was causing a fuel problem with a Dodge Van I had