This frickin fuel supply deal, man!

[derekm803]

I have a 71 F100. 302/3 on the tree. The thing will sit there n run for like 10 mins then slowly stop getting fuel. I have the glass in line filter and can see the level in it slowly dropping off til it starves out. I pulled the tank, had it it boiled n lined, new fuel pump, new rubber lines everywhere the metal lines meet, blew out the metal lines, all clamps are good n tight, vent lines blown out. I just have no idea where to go from here besides the the high pressure pump. It's been doing it every since I got the thing. While the tank was out I had it running off of a one gallon tank under the hood. It would run longer off that tank, 30-45 mins but still would eventually do the same thing. The first time I fired it up after re installing the tank when I noticed the level starting to drop off I took the gas cap off and it lost prime, the filter went completely empty. Let it sit there n cool off and it'll fill the filter completely up when you first crank it but a few mins later it'll start dropping off again. Before I pulled the tank I tried a couple electric pumps with the same results but they were both the low flow variety. Kinda at wits end, here. Don't wanna just keep throwing money at the thing but can't just let it sit there, either

[idaho_cowboy]

These mechanical fuel pumps are notoriously bad. Even when new, often I'll have to have them replaced. I'd start there. Don't assume that because it's new that it's working.

- Joseph

[markguiver]

Might want to pull the tank and make sure there is no crud down in the bottom getting sucked into the pickup tube, and also check the pickup tube for holes in it. Even a small pinhole in the pickup tube above the fuel level will cause it to lose prime. Another thing you can do is get a vacuum/fuel pressure tester and see what the pressure does when while it's running good and when the starvation starts. Seems to me like the system is sucking air somewhere before the pump.
Mark.

[derekm803]

The tank has been pulled, boiled out and reclined. I'll look for a fuel pressure gauge. I tightened the hell out of every connection from the tank to the carb to try n make sure I wasn't sucking air. What about vapor lock?

[markguiver]

It could be vapor lock if your fuel lines are close to the exhaust system under the truck. My truck used to vapor lock until I insulated the lines where they were close to the headers. That worked until a couple of years ago when they started leaving ethanol in the gas year round. Started vapor locking again during the summer because the Obama gas boils at a lower temp. then pure gas. I ended up routing my fuel lines outside the frame rails. That cured the vapor lock. When it would vapor lock I could see it percolating in the clear plastic filter up by the carb and hear it as well. Are these symptoms showing up when it dies? One thing you can try; pull the fuel line loose under the truck and drain it into a gas can. The siphon should drain the tank unless there is a restriction or it is sucking air between the bottom of the pickup tube in the tank and the end in the can.

Mark.

[derekm803]

Picking up my replacement "new" fuel pump in the morn. when i took the old(new) one off i stuck my electric pump back on it. It would pull fuel up to the filter but not prime it all the way. Plus, the truck wouldnt stay running with it on. Like it wasnt even pumping enough to fill the bowl. When it was running last on the manual pump i did notice a small bubble popping up at the infeed side of the filter. maybe i am sucking air somewhere. Ill pick up a couple more feet of fuel hose tomorrow too n try again. Gotta double check the location of all the metal lines in relation to the exhaust, too. Anyone had a situation where the OE 30gph manual pump just wasnt strong enough to keep fuel coming out of that vertical tank behind the seat?

[Manny]

Picking up my replacement "new" fuel pump in the morn. when i took the old(new) one off i stuck my electric pump back on it. It would pull fuel up to the filter but not prime it all the way. Plus, the truck wouldnt stay running with it on. Like it wasnt even pumping enough to fill the bowl. When it was running last on the manual pump i did notice a small bubble popping up at the infeed side of the filter. maybe i am sucking air somewhere. Ill pick up a couple more feet of fuel hose tomorrow too n try again. Gotta double check the location of all the metal lines in relation to the exhaust, too. Anyone had a situation where the OE 30gph manual pump just wasnt strong enough to keep fuel coming out of that vertical tank behind the seat?

That would be if it was a failed check valve or so makes it not pull properly. Cracked dip tube all that stuff. Your going the right way cleaning the tank and such. Does it have any old dual tank valves of anything like that on the frame? I would hook a vacuum pump up the to line at the pump. then cap off the line in the tank pull a vacuum and wait to see if it bleeds down. Could be rubbed a pin hole on the frame somewhere at the cross member is the only thing I can think of.

[derekm803]

I'm getting back on it tomorrow with the new pump and some new rubber. Gonna try n inspect every bit of it real well. Pretty sure it was never a dual tank truck. My high volume pump should be here before the weekend, too. Anybody wanna save me some thread searching n post a link to a nice horizontal tank swap thread to study in case I get to wits end n decide to go that way? Thanks

[sargentrs]

Scout tank
https://www.fordification.com/forum/vie ... =3&t=77791

Mustang tank
http://www.fordification.com/forum/view ... =7&t=46022

Tech pages
https://www.fordification.com/tech/fueltank01.htm
https://www.fordification.com/tech/fueltank02.htm

[derekm803]

Thanks!

[Busboy]

It worked for 50 years with the existing tank and supply system. Keep looking for the problem rather than changing out tanks.

[derekm803]

It's just a simple. Single line up to the pump. Just put my second new one on there n its pulling less than the first

[Busboy]

Are you sure the eccentric on the cam or gear is in good shape?

[derekm803]

No, im not. I have thought of that but ive tried 2 electric fuel pumps with no success as well.
If i get a fuel filler neck to fit a vented gas cap I can do away with that Quagmire of a ventilation system tho, right?

[Busboy]

That quagmire isn't causing your problem. I'm one of the guys who like to keep things all original. It's an OCD thing.