I just got a '68 f-250 ranger, camper special. I beleive it has a 390 with a 4 barrell edlebrock carb. The problem is, it starts great,drives and idles terrific,but about after 20 minutes or 10-15 miles, the idle startes ...chuging,like I'm running out of gas and then dies. I'll get it to the side of the road and turn it back over,and after a few tries the idle will be clear or I'll rev it till it clears, or it wont' respond to me reving it because the idle doesn't respond to me pressing the gas at all, and I'll literally prime the carb with my gas can to get it to re -start so I can limp it back home. whats the problem? whats the solution?

side bar question...could you put in a 351windsor or clevland to replace it? could you put a fuel injected 351 to replace it? would it even be worth it to save some gas mileage? I don't carry a camper or anything in the bed, and probably never will, but if I did want to would the 351 be enough?

I thank anyone that has some advise, because I really like the truck, but this problem is a pain in the neck!

Welcome to FTF. It sounds like you have a fuel problem. Possibly a plugged up fuel filter or carb. issue. If you were to swap to a 351 you would need a different trans as well. It won't bolt up to the new engine. I would see about getting this issue resolved and you might not have to worry about changing engines at all. I would begin by checking the fuel filter. When was the last time it was changed?

It sounds like a fuel problem to me as well. Start with the least expensive first.

Check the filter if that dont fix it id say vapor lock. The fix for that would be either an electric fuel pump or a higher pressure mechanical pump.

1985 Ford F-150 said:

Check the filter if that dont fix it id say vapor lock. The fix for that would be either an electric fuel pump or a higher pressure mechanical pump.

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What would cause vapor lock ? Is it only a temperature issue. Thanks

How much rubber fuel line do you have ?

Try to keep it to a minimum as rubber retains heat.
Steel will allow fuel to stay cooler
Rubber also allows air to be sucked in causing fuel delivery problems.

Do you have headers ?

Under hood temps bein too hot or fuel line too close to the motor is what causes it. What happens is the fuel gets so hot it boils and turns into a vapor and starves the motor for fuel.

Reaplace your fuel filter, rebuild your carb and run a bottle of fuel line drier through it.

sounds like a weak fuel pump. disconnect it at the carb and have a friend hold something to catch the fuel and see how much its pumping.

Vapor lock is pretty rare in these trucks, but not unheard of. Sounds like a fuel filter to me, too. I've gotten in the habit of installing an electric fuel pump on all of my older vehicles, makes it easier to get them going if you run out of fuel (not that I ever do!), and takes care of vapor lock issues.

Vapor lock doesn't usually happen until it is 100*F with no breeze.

Like I said before remove as much rubber fuel line as possible