Double check your timing @George.
@“Rod Knox” … double checked the ignition timing, it’s ok. Next I reconnected the retard vacuum hose to the distributor from the intake manifold, it yields a 3 degree retard ok, but made no difference to the starting problem. Next I adjusted the idle mixture screws, did this with the air cleaner removed, started at 2 full turns out, then turned them in, in increments CW direction, 1/2 of a turn increments, until idle speed noticeably reduced, which was 1 full turn, then backed them both CCW 1/2 turn back to where the idle rpm seemed pretty stable. Runs a little better, but still no difference in the starting. While the air cleaner was removed I visually verified the accelerator pump is working, squirting fuel into the carb.
I noticed that starting the engine after the engine had heated up to normal temperature, then turned off and the truck sat for 15 minutes, it was even harder to re-start then. When this happened, instead of just cranking some more, I removed the top off the carb and took a peek at the fuel level in the bowl. It was lower than I expected it to be. The dry float setting checked ok at 1/2 inch (from the rim – no gasket – of the carb to the top of the float in the closed position), but when I looked in the bowl the float wasn’t in the closed position, and the fuel was lower than it would have been if the bowl had been full and the float in the closed position.
So I tried an experiment, manually filled the fuel bowl so the float was in the closed position, fuel level about 27/32" from the rim, which is what the service manual says is the spec for the top of the fuel. Put the top back on the carb, same starting problem.
So the starting problem seems unrelated to the unexpectedly low (to me) fuel level in the bowl.
I also checked the position of the fast idle screw on the fast idle cam, that checks out ok. I experimented w/that setting to see if it affected the starting problem, had no effect.
I also lubed the choke linkage and where the throttle rod goes into the casting with a few drops of wd 40. Didn’t seem to have any effect on the starting problem, but the choke linkage seemed to operate a little smoother.
So the results to summarize, after doing the various stuff above, the engine is running maybe a little smoother due to the adjustment of the idle mixture screws, but is still stubborn to start, especially when hot. And there’s an unexplained drop in the fuel level in the bowl after the engine is turned off, but like I say, maybe that is just how the fuel level behaves w/ Ford carbs. The shop manual says the way to check the fuel level (wet level test) is with the engine running, not stopped. So what it measures when stopped probably isn’t important. Since the dry float setting is ok, and the float is floating ok, I’m thinking the fuel level is unrelated.
One more piece of information, might be a clue, I discovered I could make the engine start more quickly (fewer seconds of cranking) when hot if I hold the gas pedal all the way to the floor and didn’t pump on the gas pedal at all. So it sort of is acting like it is flooded a little.
Any ideas?
Sounds like it’s vapor locking. The fuel level in the float bowl will be lower than normal because the gasoline in it is being boiled out and dripped into the intake. That leads to a flooded condition.
Sometime when the engine is fully warmed up on a hot day you might wait 5 minutes, pop the hood, take the top off of the air cleaner, and look down in the carburetor bores to see if there is any gasoline being dribbled. You should see nothing at all.
If you do see a dribble of gas then it’s vapor lock.
Something I have seen a couple of times with Ford carburetors (and it’s not common) is that several of them had porous castings. The first time I ran into this it ate me up figuring out what was going on. The engine could be run, shut off, and 4 or 5 hours later the float bowl would be empty.
I finally pulled the carb, cleaned it up a bit, filled the float bowl with gas manually, and propped the carb up on the bench on a pair of containers.
I pulled up a chair and flashlight and started watching and waiting.
About 10 minutes go by and I see a drip. Five minutes more another drop. At that point I disassembled the carb and got the clutter out of the way. Gas in the float bowl again and then in 10 minutes I could see an area in one of the bores start getting damp; followed by a drip.
I also ran into this on a 2 barrel carb on my sister in law’s Mustang.
In yet another incident I installed a reman carb direct from the Ford dealer that suffered the same problem. The Ford dealer was a bit puzzled when I took it back and pointed out the issue but was understanding and ordered another which turned out to be fine.
As I said, that’s rare but something for consideration.
In all of these porous casting carbs though the common trait was that the float bowls would be completely empty.
Good ideas @ok4450 … thanks for your well-informed feedback. I got to thinking the same thing, that somehow the gas in the bowl is making its way to the intake manifold w/the engine off. I was thinking I’d have to remove the carb, put it on the bench, and fill the bowl w/gasoline and watch for leaks. Like minds think alike I guess! … 
I have already looked down the throat of the carb when the engine is hot, didn’t notice any dribbling of gas out of those little holes down near the throttle plate. But I didn’t look very carefully either. That’s my next step, before removing the carb for the bench test.
The only problem w/this leaking-carb theory is that the same carb didn’t do this before. The sequence of events went like this, same carb
- starts perfectly, runs perfectly (for years)
- starts perfectly, runs poorly (for a few weeks)
- carb clean & rebuild
- stubborn starts, runs perfectly
I do have a little new data to report. I used a mirror and discovered some leaves and sticks debris in a portion of the hidden part of the air intake path from the grill to the air cleaner, which I blew out w/a shop vac. & I removed the plug and hooked up the vacuum advance line from the carb above-throttle port to the distributor vacuum advance. So now both vacuum ports to the distributor are connected, the retard to the intake manifold, and the advance as described above. One or both of these seemed to improve the stubborn start problem somewhat, but not entirely. As before, the engine continues to run perfectly once started, cold or warm.
OK, new theory for the stubborn start problem. I’m going OK’s “something’s causing the carb to overheat” idea. So it would have to be something different now than before the rebuild. I can’t think of anything in the rebuild. There’s still the same metal egr spacer between the carb and the intake manifold, same gaskets, etc.
But there is still one difference. In add’n to rebuilding the carb, I fixed a damaged choke heat riser system. Tha’st the system that routes cold air in a tube from the top of the carb down to an extension of the exhaust manifold where the cold air goes in the bottom, and hot air comes out the top, then back to the choke ass’y to heat the bi-metal spring, & from there the air is drawn into the intake manifold. Before the rebuild that system had rusted off at the exhaust manifold extension. The tubes were just hanging there. I installed a generic “fix the choke riser” kit, and so now those tubes actually draw cold air in, heat it, and send it up to the carb. The metal tube from the exhaust extension going to the carb now gets very hot, too hot to touch after the engine warms up.
My theory is that this system, now fixed, is working too good. And is heating the carb to the point it is boiling the fuel. What do you think?
The vapor lock problem can occur with any vehicle and any carburetor. This is made worse by unleaded fuel. Back in the 70s an 80s there was all kinds of vapor lock grief even on EEC controlled carburetors.
The engine heat has a tendency to rise after the engine is shut off. The heat soaks into the carburetor and can start the gasoline boiling and expanding. The gas is shoved out of the primary bore discharge tubes and so on due to the float bowl pressuring up a little.
About the best thing that can be done to prevent vapor lock is to use rubber fuel line on the engine and use a fiber or phenolic spacer block between the intake manifold and carb.
Drag racers running carbureted engines get around this issue by using a can with a metal fuel line coiled inside of it. The can is then packed with ice, dry ice, or a combination of dry ice and alcohol. All done solely to stop vapor lock by keeping the gasoline entering the carb cold.
Not really practical for street use.
Quick summary: 70’s Ford truck 302 V8 begins to idle and run poorly. Suspected some combination of deferred maintenance & fuel contamination. The fix: I replaced the spark plugs, added a second fuel filter, replaced the original fuel filter and air filter, fixed the broken choke heat stove system, and rebuilt the carburetor, which included replacing a badly damaged egr spacer gasket, likely a major contributor to the original problem, as it was causing a vacuum leak. This all fixed the poor idle and run, but introduced a new problem: stubborn starting. It took 5-10 seconds of cranking to start sometimes, when before all this work happened, it would always start on practically the first “r” in “rrrr”, maybe 1/2 second to crank, pop, & start up. The only obvious problem I could spot was the fuel level in the fuel bowl was lower than I’d expect it to be.
Posters @ok4450 , @“Rod Knox” , and @Nevada_545 all offered up opinions, Ok and Rod I think focusing on gas percolation from an overheated carb body for the stubborn starts, and Nevada mentioned a possible leaking power valve as the cause of the original problem. I suspected the second fuel filter for the stubborn start problem, so I removed that, but no help.
The actual problem: The new power valve (replaced as part of the rebuild) was leaking gasoline into the intake manifold with the engine turned off . Excepting percolation, the power valve is about the only way gasoline can leak from the carb bowl into the intake manifold without the engine running, the other ways would require gasoline to move uphill. I discovered this leak by removing the carb, building a little stand to sit it on, and filling the fuel bowl with fuel. It started dripping gas out the bottom immediately.
Replaced the power valve with a new one and associated gaskets, no leaks, and no more stubborn starts. 1/2 second crank & start returned.
Lesson learned: A carb rebuild requires that the rebuilt carb – before installing it back on the engine – be put on a stand and gasoline poured into the fuel bowl to verify it doesn’t leak.