It doesn’t appear to be leaking from filter so tape won’t help and can only hurt as Rod Knox pointed out. Here’s what I’d do- remove carb. Drain bowl. Remove bowl. Attach short length of hose to fuel inlet. Invert carb so float is closed by gravity. Observe operation. If nothing seen, blow in hose. It should totally blocked. If you can blow through, something is wrong with needle or seat.
W/the carb on the work bench OP could probably rig up a reservoir of fluid above the level of the carb, with a tube to the carb fuel inlet, and observe if the float action shuts off the fuel at the correct level. I wouldn’t use gas to do this experiment myself. I’d probably do it with water, then make sure everything is drained and dried and flushed w/gasoline quickly afterwards.
I tried this, and it seems to seal pretty well, but it seems that some air is leaking through somewhere, because it doesn’t feel totally sealed. When I was first testing, there seemed to be a pretty significant leak coming from where the fuel filter screws into the carb, so I first tried removing the tape (which didn’t help) and then I replaced the fuel filter, which seemed to stop that leak, but I still can blow through the fuel line. How can I figure out where the leak is coming from?
Actually upon testing again, the seal seems to be pretty much perfect blowing through the line with the carb upside down. I previously tested with the air horn removed, but this time the whole carb assembled, the seal is solid. So what does that mean now?
Hard to tell, but my guess is the float is not adjusted or the needle and seat are not working properly.
1 Like
The fuel inlet seal could be working fine , but if the float doesn’t float – b/c it is defective – or it floats ok but the level is set incorrectly – see Tester’s post above – the fuel could still flow in through the valve and overflow the bowl. A wet bench test of the float mechanism is how to diagnose that. Same as you’d do if your toilet tank was overflowing. If the float is working and the inlet seal is sealing and the level is set ok … hmmm … The way carb’s work in operation is sort of like how you suck cola from a glass. Your mouth and lungs form a vacuum force to pull the fluid level above the level in the glass. Carbs work the same way. When it is working correctly the only paths from the fuel bowl to the intake manifold (below the carb) require the fuel to be sucked above the level in the bowl. The running engine provides that suction force. So if it leaks without the engine running, the leak would have to be some part below the fuel bowl level not sealing correctly, like the power valve, the accelerator pump, the fuel filter, or the idle mixture screws. If it leaks only when the engine is running, besides totally defective carb internals, I can’t think of anything that would cause that besides a problem with the fuel inlet & float mechanism. You didn’t accidentally forget to install the jets, right?
Did you install a new accel pump diaphragm as part of the rebuild? Ruptured pump diaphragms are common sources of external carb leaks. What about the power valve, is it and it’s gasket new?
This may be a dumb question, but how can I properly bench-test the float when it is mounted to the air horn assembly?
From talking with some co-workers of mine who work on cars, they think it is likely to be a problem with the needle and seat since it seems that it is a problem with the float. Could I put the old ones back in, or should I order new ones?
My Ford truck’s 2100 2 barrel carb’s air horn just lifts off after removing a bolt, independent of the float ass’y. It sounds like that’s not the way it is configured on your 4 barrel. So I can’t offer much guidance there, sorry. You can still presumably set up a bench experiment where you gravity feed a bottle of liquid into the fuel inlet port, and monitor the fuel level in the bowl; at least you should be able to confirm whether it overfills the bowl or not or otherwise leaks. If the float and needle/seat are working correctly, the fluid flow will completely stop when the bowl has reached the proper fuel height, and there will be no leaks at all dripping below the carb. Suggest to try that first, before replacing parts.
A carb clean and float adjustment is where I would start, I do not know if these are replaceable seats or not, but some buildup if foreign stuff can cause a failure.
Without an insightful comprehension of the basic operation of a carburetor it is difficult to diagnose a problem and it seems that in this case the comprehension is lacking. A leaking gasket on the inlet seat, a damaged viton tip on the needle, a cracked float, a misaligned float tang, etc, ad nauseum, leads to a great deal of frustration if the diagnostician isn’t willing and able to think through the situation and investigate the possibilities. Maybe a factory rebuilt carburetor would be a worthwhile option at this point.
So I got a factory-rebuilt carb, but I’m now still having the same issue that caused me to start the carb rebuild in the first place where the car will start right up but then immediately stall, or it will run for a minute or two and then stall. It never stutters before stalling, it just cuts out.
I also tried using starting fluid, and that didn’t seem to help, which to me indicates an issue with the ignition system, but I don’t know how to diagnose it from there.
The ignition module is the most problem prone piece in the ignition. Those modules can be identified by the color of the plastic spacer on the wires where they exit the housing. Several years ago all the McParts stores had bench testers for those modules and repeatedly testing them would often successfully identify those that started the engine then failed after running a short time. Call around to see if one of the stores has the tester.
Remove a spark plug wire from number 1, and connect it to a spare spark plug. Hold the plug against an engine ground, a helper cranks the engine, you should see a healthy spark at the tip of the plug firing several times a second as the engine cranks. Be very careful as the engine may start up. If you don’t see that spark, and the engine didn’t start, you’ve isolated the problem to the ignition system. It could be something as simple as a bad ignition switch. If your Lincoln uses a capacitive discharge electronic ignition module (but still has a distributor w/ points or electronic sensor on the dist shaft) , those are known to fail in weird ways. Make sure nothing wet is getting dripped or sprayed on the module, as any dampness at all will cause it to fail and the engine stalls.
First things first though, do the experiments required to decide if the problem is ignition or fuel.
My first carb rebuild experience ended in the same result as yours: purchasing a rebuild unit. 
No worries. I wish I had kept the original carb though and not turned it in for the core fee. I’m pretty sure I could have fixed it.
I replaced the rotor and cap, and I got an in-line spark tester. Using this tester, I can see on the failed startups that I get spark while cranking, but as soon as I stop cranking after I feel the engine catch, the spark immediately stops (and the engine immediately dies).
Check the “primary resistance wire” from the coil to the ignition switch:
I’m getting ~12V at the coil when the key is “ON”.
How about during “START” and release back to “ON”?
There’s two power paths to the coil. One provides full battery power and is only used during cranking, to make it easier to start the engine. the other kicks in after the key is returned from start to run (or on). There’s a resistor in that path, to reduce the power, in order to prevent burning out the coil as the engine runs for a long time. Insightful’s diagram shows the two paths, the one from the starter relay provides full power during cranking, and the one from the ignition switch has the resistor in it. Typically it isn’t an actual resistor but a wire that has build in resistance due to the alloy used in the conductor. I think that part (the wire) is called the ballast resistor, if you need to order one.
If that ballast resistor had too high of resistance, or a bad connection somewhere, you might still measure the full battery voltage at the coil when the key is in “on”, especially if the points happened to be open. The problem would show up when the points closed, as that would cause current to flow in that wire and the voltage at the coil would decrease. During cranking the full power path would power the coil ok, but as soon as you returned the key to run, with the points closing, no more spark. This symptom is not uncommon here for older Fords.