I recently joined this cite -- not because I am a truck owner (I am the original owner of a 1978 Mustang II Ghia), but because I saw some posts on this forum answered by "fme400" - pertaining to the 2150 carb, which I believed to be quite knowledgeable. Sadly, I have not run into this expertise on the Mustang forums, although I am sure that it exists.

In the last couple of years I have run into the problem of cold cranks requiring 20-25 seconds of cranking before the engine fires. Once fired, it runs smoothly, and restarts are instant. I have written this off to fuel evaporation with all of the EPA changes dumped on the refiners, and because I don't drive the car daily. But, I'm not sure.

I just completed my third rebuild of this carb in 30+ years. I replaced the choke pull-off, which had a slow vacuum leak, and the electric choke thermostat heater, both still available through Rockauto.com. But, even with the carb bowl one-third full, it still required 20 seconds of cranking. Have others experienced this situation for a carburetor of this vintage, or do I have a unique problem?

The fast idle screw/cam setup is unlike anything that I have seen. It does not match the pictures in the carb rebuild kits, nor does it match anything in my overhaul manuals. I will try to upload a photo below. There is a linkage on the end of the throttle shaft, which limits the amount of rotation of the cam. This may have been a Ford adjustment late in the Mustang II series, but which never made it to the manuals. Regardless, this tells me that fast idle speed might be affected, but I would not think that it would affect a cold crank. The choke pull-off does its thing, and the choke thermostat heater returns the choke plate to a vertical position as the heater element warms up. Maybe the cold cranking problem is not even related to the carb setup? Coil? Or, today's gasoline evaporates so rapidly from a non-fuel injected rig that this is something that I will simply have to live with.

Obviously, any observations are most welcome!

Gordon Biggar
Houston, TX

 

Wondered about this myself and have seen exactly the same thing with 2100 series. If the truck is not used for several days, even though the bowl has fuel, it will not start right away.

This is hard on the starter, solenoid and battery. Thought it might mean a bad or leaking power valve, gasket, etc and but this seems not to be the case. The key is that the power valve reservoir is losing its prime over time, so there is no pump shot at the time when the accelerator is pressed.

Many others have observed this too. If you can figure it out you will be a hero. A teaspoon of fuel down carburetor throat is enough to get it started right away.

Oh, welcome to FTE btw

 

Not a very comforting reply! I am trying to make contact with Shell Oil to see if they can shed some light on the situation; something (increased percentage levels of ethanol?) must have been added to the refining process to cause this - dictated by the EPA, no doubt.

At first I thought that there was a leak from the enrichment valve, which one would not see externally, and which I have never replaced until now. But, the gaskets were in great shape for having been left alone for over 30 years.

I have used StarTron in my fuel tanks for a number of years now, since I am not a frequent driver of my Mustang, nor of the Model "A" Ford. But, it has not helped the situation.

In looking at a diagram of the idle system, is it possible that the mixture screws are somehow restricting the idle discharge hole? I doubt it, though, because once started, the engine idles perfectly.

Back to the drawing board. Thanks for the response.

Gordon

 

Fuel characteristics have changed over the years. One of them is called the Reid index iirc. Has to do with the susceptibility of fuel to cause vapor lock. Since virtually all cars and trucks today are fuel injected, this is no longer a concern for gasoline refiners.

In high temps you can watch fuel boil in the carb bowl. After shutdown some of the fuel does boil or evaporate out of the carb as earlier models had open vents but not all of it. Some people suggest that the fuel is being drawn somehow back through the fuel pump or somesuch too. Maybe a fuel shutoff valve at the carb would prevent that.

Some recommend installing an inline electric fuel pump to prime the carburetor because of this problem, so it's well known.

 

I have restored Model "A" carburetors for many years. A hard start condition is not a problem, because these are downdraft carburetors. When shutting down the engine, one can close the fuel valve while the engine idles until the fuel bowl is drained.

For a reverse flow of fuel through or to the fuel pump would require fuel to get past the inlet needle and seat. The suction would be pulling the needle valve down to its seat, so I wouldn't think that this would be a likely condition.

Carb rebuild kits show at least two choke adjustments. The first pertains to the choke valve pulldown adjustment, which opens up the choke plate slightly, based on engine vacuum. A second adjustment, which I don't totally comprehend, pertains to a choke unloader measurement. This would seem to be counter to the concept of the choke plate closing totally at start-up in order to enrich the fuel mixture. But, I would still expect some firing, which does not occur.

Gordon

 

Yes I agree with you, and not saying I subscribe to any of theories though is a very common complaint, neither of us is the first to notice this "feature".