I bought my 1976 F250 Ranger XLT about three weeks ago and last week it developed a problem with stalling/cutting out when running.

I changed the tank side fuel filter, the electric fuel pump, the mechanical fuel pump on the block, and as many of the fuel hoses as I could get to and it seemed to solve the problem with the truck running fine over the weekend.

Then this morning it started again. The truck will run for a bit and then die out, leaving me to coast to the side of the road and wait a minute or two before I can restart it again. When I check under the hood, the fuel filter on the carb is almost completely empty after each cut out. Then when I get it restarted it'll run for a little while and then cut out again. After each cut out, the time between cut outs is shortened, but then if I leave it longer between restarts, it seems to get better. Obviously not an ideal situation when you're trying to limp it home!

Anyone got any ideas? This is my first project truck and my first time working with a V8 and Carbs, but I'd like to think I'm fairly switched on otherwise

 

I wonder if it's a fuel tank venting issue - try running with the fuel cap off and see if it makes a difference - if so, the vent line to the canister (for evaporative emissions) could be blocked, or the vented fuel cap (for non-evap vehicles) could be faulty.

 

Sorry, I forgot to note that it's got the 390 V8 with a Holley 600 Carb on it.

 

Next question would be how do I find out if it's the evap or non-evap type that I've got? There's no obvious vent on the fuel cap, but it doesn't tightly seal against the filler neck, so shouldn't be an issue with pulling a vacuum in the tank.

 

Another thing I'd like to ask/mention is that on the truck I have, there are two fuel pumps. One electrical pump underneath the driver's door taking suction from the two tanks, and the engine mounted mechanical one. Now I didn't know any better and so have replaced both pumps, but reading through the Haynes manual for this era of trucks, it's telling me there should only be one fuel pump? The mechanical engine mounted one?
Struggling to work through what this might be but when the day dries up a little, I want to get back into it.

 

Is there a charcoal canister under the hood on the passenger side frame rail? It would either be a round blue can like this:



or a plastic canister shaped like these:



(canister type depends on model year - the metal one with rust holes is what I removed from my '74 truck; the plastic ones are from a mid-80s donor vehicle). The original canister on mine was on the inside of the frame rail, just a little further forward than where I've got these mounted.

If there's a charcoal canister, it's a vehicle that was originally equipped with evaporative emissions control - there should be a vent line from the tank running along the passenger frame rail to the canister. These systems capture the vapors from the gas tank in the charcoal canister(s), then breathe them into the engine to be burned under some conditions rather than releasing them to the atmosphere; they use a sealed gas cap and rely on the evap system to vent the tank. Vehicles without this system have a vented gas cap to allow the tank to breathe. Either way, if the tank is completely sealed off, the fuel pump will be pulling a vacuum on the tank and eventually not be strong enough to draw any more out.

I see you have dual tanks; does the problem happen on both tanks? See if loosening/removing the gas cap on the tank that you're running from when it happens clears it up or not. If not, the problem is something else; if it does, it's a venting issue.

As for the electrical pump, it is not original - sounds like something a previous owner added ... possibly in an attempt to work around the same problem you're encountering.

 

If it's not an issue with the tank vent, you might check that any rubber lines are in good shape/not collapsing, etc. Replacing every rubber line between the tank(s) and the pump has helped some people with similar symptoms.

Given that it seems to be either temperature or run-time related, I would suspect either venting or maybe vapor lock - if the engine is always pretty hot when this happens, it could be a thermal issue with the line from the pump to the carb or the carb itself - attention to routing, heat shields and/or phenolic spacers could help with those issues. Depending on where your fuel filter is located, I'm not sure if I'd expect it to be starved in that case though...

 

not to hyjack this but bkaul did all truck that have these charcol canaster have the evap stuff, because i have the tank but mine is not to bad, should i hook it back up or remove it?

 

I've just had a look where you suggested and I can't find the carbon filter canister you referred to. Could it be located elsewhere? I've looked about and can't find it.

I want to give it a try with the gas filler cap off and see if that does the trick. I've not used both tanks before now as I'm not 100% convinced on the changeover switch, although it does seem to work. Last time I was messing about with it was right after this all started last week.

Should I just remove the electric fuel pump then or wait until I've got it all sorted first?

Think I'm going to have to call in some help with this...

 

That's where it would be located - your truck probably either never had it or it's been uninstalled. In that case, you should have a vented gas cap that allows it to breathe. Worth trying w/o the gas cap just to see.
Hmm ... can you reproduce the problem running the engine in the driveway? I wonder if you get into the situation where it's not running, if you turned off the electric pump so it doesn't spray everywhere and ran the mechanical one out of a gas can instead of the tank, whether it would still die or if it would run reliably. If it still dies, the problem is more likely vapor lock between the pump and the carb, or with the needle valves or bowl vents in the carb; if it runs in that case, the problem is more likely between the pump and the tank.

If the problem only occurs on one tank, that obviously isolates the problem somewhat: could be rust, etc. in the tank clogging the sump or a bad line between the tank and valve.

The solenoid valve that switches between the tanks is another possible culprit - could be worth bypassing it and running from only one tank or only the other, as another test.
The charcoal canister is only used for evaporative emissions control, yes. There should be a vent line from the tank and another line up to the intake. I like to hook 'em up on mine: if not, you're literally letting fuel you bought evaporate away instead of using it, and you'll have a gassy smell around the truck on hot days. No performance penalty either way...

 

I know this isn't really in the spirit of the forum or doing things myself, but I've called a mobile mechanic to come and take a look at it and see if he can figure out what's going on.

I took another look at the filler caps and they're both vented and don't seal tight against the filler necks, so it shouldn't be drawing a vacuum in the tank that the pump can't overcome.

I would say you're right in saying that the electrical fuel pump has been installed to get round a similar problem in the past and that I'm now having to deal with that problem and sort it out properly.

Do you know if there is somewhere I can buy the Evaporative Emissions Control kit from to install this to my truck? I do smell the gas fumes around the truck on hot days (and we get some of those here in Florida!) and I'd rather it go back to good use than getting the bugs high! I checked the hoses from the mechanical pump to the carb (only ones I haven't replaced yet) and they look to be fine and have a good amount of resistance to them so I don't think that's it.

Hoping that this guy who's coming out can give me a solution to the problem!

 

The fuel tank is different (has a vent with a rollover valve for the "EEC" vehicles, while the "non-EEC" tank lacks the extra vent tube) - then there would be a vent line running from there up to the front. I think Inline Tube may reproduce that, or you could bend a new one yourself. Then you'd also need a charcoal canister (With two tanks, they may've run two canisters, or may've just run one and teed the vent lines together, not sure; with 4V carbs in the 80s, Ford ran 2), a sealed gas cap, and the lines to hook it up. It seems some of the early evaporative emissions systems (including at least some of these trucks) ran a ~3/4" line directly to the air cleaner; later model vehicles (not sure if later than these trucks or not) ran a vacuum-operated canister purge valve controlled by the emissions (EGR) port and teed the canister purge into the PCV line to the intake. That's what I'm doing in the picture above with the two plastic canisters. I've never seen anyone sell it as a kit - you'd just need to piece it together yourself.

 

Update:
SO I had the mechanic come round and take a look and he's convinced it's the carburetor. We had the engine running in park, and it was running with a high idle, but it was running. Almost immediately after putting it into drive and me keeping my foot on the brakes, the engine would splutter and die out. Because I finally had two people there when it happened, I was able to see the filter going to the carb and it was still filling right up until the engine died, and then running back to the mechanical fuel pump (hence why it was bone dry when I was seeing it before!). It's probably good for me to note here that we had a spark indicator on as well and we were getting good strong spark pulses to the spark plugs as well.
I looked on YouTube and found how to adjust the floats on the carb, which I've done with the help of my neighbor and the idle is running much better, and I was able to run the truck round the development without any issues, but as soon as we got on the road and I had to give it some gas, the engine died again.
When we followed the instructions off the Holley website and adjusted the floats, it was clear the carb was getting too much gas (pouring out the sight screw holes when I undid them) and so we adjusted back, but it still seems as though the carb is giving too much gas and flooding the engine.
My neighbor got in touch with his uncle who knows a thing or two about carbs and he thinks it's the power valve that's allowing too much gas into the carb. Does this sound about right? Has anyone had a similar issue and found the carb to be at fault? Would rebuilding the carb solve the issue? I've seen they've got rebuild kits at Advance Auto Parts with instructions, so I figure I'd be good with the rebuild, but how difficult would it be to do the setting up once the carb is back on the truck?
Any and all advice welcome, because I'm wanting to get to the bottom of this and fast! Oh and we checked the ICM and the fuel pump relays and all good on those two fronts according to mobile mechanic dude.

 

I think you're on the right track. If fuel's getting to the carb and you've got spark (not an ICM or coil overheating issue), the problem does sound like a mixture control issue at the carb. Sorry for going so far down the fuel supply path - I was thinking we were looking at fuel starvation from your description of an empty filter.

Rebuilding the carb is a good idea. A blown out power valve would cause issues along these lines, and you have to disassemble to get to it and would fix any other problems while there anyway. A lot of people recommend the Holley kits over auto-parts-store ones. I used one recently when I re-did my 4180C, and can say at least that the instructions are a whole lot better especially as regards adjustments, and it also had a few more parts than the Wagner kit that O'Reilly sells.

 

Havent had my hands in a Holley (all motorcraft here) but I'm glad you seem to have narrowed it down.. Carb issues can have you chasing all sorts of rabbits