My first post in the forums: I really appreciate all the resources and knowledge in here.

I'm the proud new owner of a 1972 F-100 4x4 manual 4 spd with a 302 and Motorcraft 2100 carb. Truck barely ran when I bought it and had sat for a couple years on a farm, so I've been going through some basics to get the engine usable (rebuilt carb/plugs/wires/ignition coil/alternator/oil change/battery). Distributor is next on my to-do; a little nervous about that. Truck had a new in-cab fuel tank installed right before I purchased it. I've got the manual choke and idle pretty dialed in and I put a vacuum guage on and adjusted the screws. I choke it on start with a couple revs; it warms up fine after a minute or two here in Georgia, I push the choke in and it will idle all day.

Took it out for a drive today and it really ran great compared to where we started a month ago. The only issue was that at higher RPM in 4th gear (around 50-55mph) the engine starts cutting out. The first time it happened, it totally quit and I just restarted it on the fly. The second time, when I knew it was coming, I let off the throttle to keep it running. No issues as long as I stayed under 50.

Any thoughts? I'm handy, but definitely an amateur when it comes to these old trucks. I've learned more in the past month about engines than in all of my previous 39 years LOL! Thanks in advance; this forum has already been tons of help.

 

Fuel pressure and flow. My guess is filter or pump.

 

BTW; Welcome to the conversation. There are things to be shared and learned. With a little bragging and humiliation thrown in.

 

Christmas is spot on, with the bragging and humiliation. He also seems to be on the right track for the fuel flow issue, sounds like you are running out of fuel in the carb. Welcome to the group.

 

Thanks guys! A couple follow ups:

1. When I rebuilt the carb, I put a brand new fuel filter on (screw in type, to the front of the carb)
2. I haven't replace the pump, but it looks fairly new compared to the rest of the engine and I'm guessing it was replaced when the new tank was installed. Is it worth going ahead and swapping out since they're pretty cheap?
3. Could this be a carb float issue? I used 7/16" as the dry adjustment when I rebuilt it. The 302 is not original to the truck and I'm not sure what year it is, so I used the most common measurement for 302s.

 

Unlikely, IMHO.

Like Christmas said, it sounds like it is starving for fuel. Fuel pumps (even newish looking ones) go bad. Easy fix.

 

It could be a problem with the gas cap or vent to the tank. Try taking a short ride with the cap off or just taped on loosely. If air can't get into the tank, fuel can't get out properly.

 

I will test this today, before I grab a pump. I've got the charcoal canister setup and the vent line is run properly (unsure if kinked or clogged), but I've been a little suspect of if the system is actually venting properly.

 

Same issue with no cap; looks like I'll go the fuel pump route.

 

I would pull the filter first and check. Just because it has a new tank doesn't mean the lines are not rusty.

 

Thanks for that. Once I pull the filter, what exactly am I checking for (or how do I inspect)?

 

Try to blow through the filter in the direction fuel flows through it. If that's difficult or impossible, it's clogged. It's also possible that a new tank was installed without a new fuel pickup assembly being installed. If so, the old one could be clogged, maybe with the remnants of the old fuel sock. I found exactly that on a '72 chevy c10 that had a really clean original tank, and a pickup almost totally clogged by the crumbled up fuel sock.

 

Congratulations on landing a pretty rare truck, there were only a little over 18,000 of those made in '72, and fewer survived since they mostly went into forestry and other hard use applications.

I am curious about the 302 - I didn't think they put them in the 4x4 trucks. I understood that the only v8 offered was the 360.

 

That’s correct. According to the VIN, it came with the 360. May look at getting one back in there down the road. It also came from the factory in blue, but now it’s green.... the life of old trucks...

 

The 302 is a better engine than a 360 for a driver. The 360 is a 390 with a 352 crank, making lower compression and power but great durability. Not much fun. If you want something more correct a 360/390 block with a stroker crank or at least a 390 crank will make a much better driving engine, especially with the NP435 gearbox and bull low. It is really a 3 speed with a stump pulling gear.