1983 Ranger won't start cold

[Fords4Us]

Good evening everyone. My 83 Ranger is dead in the driveway after a very difficult cold start which then stalled. And it's not even that cold outside, at 40F. This has been a very long-standing problem with this truck, but today was the worst yet.

I should note here that this is a duraspark conversion truck, so all the computer stuff has been physically removed. I've got a purely mechanical carb now. Still have the electric choke, which I'm starting to suspect isn't working correctly. During that conversion I also switched out the standard fuel jets for a pair of #46 jets, which are two sizes smaller than what it was delivered with. Over the summer I was having issues with it running too rich so I kept leaning out the idle mixture screws. I would expect that now during cold weather it would be near ideal, or even a little lean.

Symptoms:
1. Any time I try a cold-start below approx 50F, it takes several attempts to turn over. The starter turns the engine like normal, and the engine "takes" like normal, but the RPMs are too low to keep going and it quits within a few seconds. So I have to start it several times before the RPMs finally are high enough to maintain the engine.
2. Giving it gas during this phase is very touchy and it floods readily if I give it even a smidgen too much.
3. Often after starting it successfully, it'll run OK for a minute or two but then idle will steadily drop and it'll finally die, even if I'm trying to keep the RPMs up.

I suspect a combination of float level in the carb, and choke problems. I let it stand for an hour tonight to deal with the flooding, and then tried to crank it over again. Still had the same problem - the engine would seem to start to take and I'd let go of the start position, but it would idle very low for just a few seconds and then die. Doing some research online I'm getting repeated hits on how a rich mixture would cause problems during cold starts, but I'm getting conflicting information on what would cause the rich mixture and how to fix it. The first thing I'm going to do is check the position of the butterfly valve to see if it's open or closed, here with the engine cold and off. If the butterfly valve is open, that would help explain a lot. I'd sure appreciate any other suggestions for what to check for and possible explanations for why this is happening. Thanks all.............

 

[RonD]

Couple of things

Duraspark often used a Ballast resistor to lower coil voltage(8volts) when engine is RUNNING, a running engine doesn't need a strong spark and it prolongs coil life.
But you need the full 12volt power when starting any engine, especially cold.
When cranking the engine with the starter the battery voltage drops below 10volts, if it is passing thru the Ballast Resistor that means coil is getting under 6volts........very weak spark.
So there is always a by-pass circuit that feeds full battery voltage to the spark system during starting, make sure you have that and it is working, test voltage at coil + while cranking starter.
Or run a jumper wire from battery + to coil + and then try to start engine, won't hurt anything, if it starts better then you found one problem

You can add this by-pass with a diode and a wire to starter relay on fender, or get a 4 post starter relay, 4th post is the "i" post, it runs to coil +

Next will be spark plug gaps, wider gap makes for better cold starts, also check them for oil residue, very hard to cold start with oily spark plugs

Why do we need a choke to start cold engine?
Gasoline's vapor point is why
Liquid gasoline doesn't burn and can not be ignited by a spark for sure
Gasoline fumes do burn and exploded
When engine is cold there is less gasoline fumes for the spark to ignite, so the answer is to add more gasoline in the hope that there will be enough fumes to ignite.
Choke plate closed means vacuum in intake during cranking will go higher and suck more gasoline in from the jets, more gasoline means more fumes.
Once cylinders fire they get warm fast, so liquid gasoline will turn to vapor when it enters the cylinders, but you still need the choke because the cold gas is dripping from the jets and running down the intake, lol, so still low fume levels
Fuel injected engines are given more fuel on cold starts for the same reasons, more gas vapor is needed, just less wasted gas running down the inside of the intake.

Compression creates heat.
Even with the choke pulling in more gas the gas still needs to be heated to create enough fumes for spark plug to ignite it.
As an engine gets more miles its compression drops, this reduces its ability to heat up the gasoline when cold.
But you have to get down under 120psi.

 

[chewy012]

Do you have your cold start screw set properly on the carb?

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