The '66 aint running right

[69supercj]

So the other day I was heading into town and got about a half mile down the road and the truck started sputtering like it was running out of gas. I would pump the heck out of it and it would cough and sputter and it finally died. Got it back home, put some gas in the tank, but I knew it had gas, just had to eliminate that possibility, hit the key and it started right up. WTH. So it sat there and ran for about 5 minutes or so and then it started doing its thing again. Its got a visible fuel filter near the carb and it was full at first but slowly started emptying out and finally was dry and thats when the motor died. So I'm thinking that the new electric fuel pump I put on about 3 weeks ago has shot craps. I could let the truck sit for a few hours or overnight, come out and hit the key and it would fire right up and the filter would be completely full. However yesterday, I started it up and it ran for about 5 minutes or so and I decided to give it some rpm's up to around 2800 or so and after about a minute or so it started to act like it was running out of gas again. But this time, the filter still had fuel in it. Hmmn. Thats a new twist. Pulled the choke all the way out and it would run and then cough and sputter and get down to almost dying and then it would idle up real fast and then start coughing and sputtering and get down to almost dying and then idle up again real fast then start the process all over again. It did this about 3 or 4 times and finally died. I've taken the gas cap off, left it on, and it doesn't seem to make a difference. Dont think its electrical, it just acts like its running out of fuel but with the filter still have fuel in it the last time it started to die, thats got me scratching my head. Any ideas or thoughts? Its got a pre-filter in front of the pump as well as the clear one up by the carb.

[69supercj]

So I just tried a little experiment with some starting fluid. Seems when its starting to starve for fuel and I spray some SF down the carb, it peps back up so that to me pretty much eliminates an ignition issue. So its gotta be carb or fuel pump or lines. I can pump the throttle lever and it squirts fuel immediately and at full throttle it pumps the secondaries as well so it seems to have fuel in the carb or at least to the accellerator pump. Maybe its got fuel, just not enough to keep it running. Fuel filter still had fuel but not as full as before.

[69supercj]

Well I think I found the problem. Pulled the fuel line just past the first filter and it flowed well. Pulled the fuel line past the fuel pump and its pumping but just barely. Seems my new pump lasted about a month. Nice.

[Macon ACE]

Dang man, it's awesome that you figured it out so fast! While reading your first post I was racking my brain trying to come up with some way to help.

[69supercj]

Well I THOUGHT I had the problem figured out but it took another twist today. I bought a new fuel pump and was getting ready to install it and I was removing the fuel line just past the fuel filter and no fuel ran out. Hmmm. Thats odd. I pulled this line yesterday and fuel flowed well. So I pulled the line in front of the filter thinking that the filter was clogged and nothing. Took the air hose and blew back through the tank and the fuel flowed like a fountain!! Guess its time to pull the tank and either clean it and replace it or ditch the incab tank and install a Mustang tank between the rear frame rails. Decisions decisions!!!

[unibody madness]

Could be something being sucked into your pick up tube,
or hole just below the fuel level, that raises above the level, when rocked, or you sit in the drivers seat?

[64 f100]

Could be a piece of lose rubber inside the fuel line acting as a valve. Also, Old fuel lines will collapse from getting soft. There are normally two rubber fuel lines on these trucks. One is directly below the cab . Also, the metal line in the tank sometimes gives problems.

Rich

[slickstysix]

I had the same issue with mine. Turned out to be a small pebble that was getting sucked up into the tube up to the bulkhead connector on the factory in-cab tank. I'd stop and the pebble would fall allowing enough gas to flow up until i got on the throttle and make it about 1/2 mile down the road. Check all of the tubes from the tank to the pump...

[69supercj]

Got the tank pulled out today and this thing is clean as a pin inside. I cant see anything at all. I guess I'll flush it out and see if I can get anything to come out. Also, which way should I bend the fuel sending unit if its reading a 1/4 tank when in fact its empty? More bend or less?

[slickstysix]

I believe you should bend it up to allow the sender to read correctly. How much, not sure.

[unibody madness]

Since it is apart, test it out of the tank. Float should point toward passenger side, and no amount of bend or straight will read fuel if tank is empty. the straighter the rod the lower it will read, but if is the correct sender it can never reach the bottom of the tank.

[Toyz]

With a given amount of fuel, bending it up will result in a lower reading if everything else is correct. John is correct, there is a stop tang on the sender assembly when against that lower tang, it should read empty. The replacement assemblies sometimes require adjustment to both rod and tang for a correct reading.
A very minimal chafing in the sensor wire external to the tank can also result in a slightly high reading.
Paul

[69supercj]

Took the tank to the station today and found a small piece of solder, about the size of a plump raisin and another small sliver of solder. Guess the larger piece was getting sucked up into the pickup tube. Only thing I can guess anyway. Got it flushed out and now its drying. Speaking of tanks, what should I use to replace the "organic" insulation strips that were used between the tank and the cab. Mine are here but they look compressed and not sure how good they are insulating. Thought about some foam rubber like you would put on the bed rails when installing a camper shell but I figured it might squeak really bad.

[Toyz]

Sounds like MacGyver and his ping pong ball trick! I used 1/8" thick rubber stripping on the tank straps.
Paul

[69supercj]

Okay here' the latest on my '66. I thought I'd found the problem with the piece of solder in the tank but yesterday I went out to start it and it wouldn't hit. Went out this morning and it fired up and it sat and idled for probably 15 minutes at least and I noticed the fuel level slowly going down in the clear filter up near the carb. It finally started to sputter and I took my mouth and blew into the tank and she pepped up and ran. Started to sputter again and same thing. Finally I just let it die. I'm 99.9 percent positive its nothing in the tank. Its almost got to be the fuel pump put it seems to be pumping fine. Guess I'll take the fuel line and stick into a gas can and see if it runs that way and if so then that should point to the tank. Otherwise if it dies, its got to be the pump right? Its also got a filter just in front of the pump and adjacent to the elbow under neath the cab. One quick question though. If you remove the rubber fuel line at the elbow under the cab, how much fuel should run out, if any. With the line coming out of the top of the tank, I dont think you will get much gas, just whats in the line itself right?

[ICEMAN6166]

One quick question though. If you remove the rubber fuel line at the elbow under the cab, how much fuel should run out, if any. With the line coming out of the top of the tank, I dont think you will get much gas, just whats in the line itself right?

the gas will come pouring out until tank is empty
same thing if you remove the hose before the pump

thats because the dip tube inside the tank goes to the bottom and its a siphon

if you remove the hard line from the top of the tank, you break the siphon.

had a problem a long time ago where i was not getting fuel
turned out i did not tighten the line down at the top of the tank when i put it in and was getting air

seems you may have a similar problem somewhere between tank and pump

[69supercj]

Well yesterday when I was working on it, I removed the rubber line from the elbow below the cab floor and no fuel came out. Took the air hose and gave it a short blast and nothing. Did it again and nothing. Third time I gave it a good shot and fuel started coming out. Anyway, this afternoon I took the line loose from the tank and stuck it in a can of gas. The truck ran for a little bit and started doing its same old thing. So I removed that pump and put on a better pump. Got it mounted and other then a leaking fitting, it sat and idled for about 40 minutes or so and never had a hickup. I hope I've got the problem solved.