Classic/Antique Car Repair: 1930 Ford Model A Running Rough, gravity feed, carborator

Question
Sir,

I have a 1930 Model A truck that my father in-law had restored.  It looks perfect, starts easily, and idles well.  However, after driving for 5 or 6 minutes it starts to sputter and try to die.  I have tried adjusting the spark advance and carborator from inside the cab, but none of this seems to work.  Any advice?  

Answer
There are so many possibilities here that I'd be crazy to make a wild guess!  It could be either fuel, ignition, or a plugged exhaust system, and the only way to sort this out is to have someone with an engine analyzer take a look at it.

If that isn't practical, check the various systems one by one, and hope you run across the problem.

Since the fuel is gravity feed, there is no pump to worry about, so verify that the fuel line valve is all the way open, and that there isn't any restriction in the line by disconnecting the line into the carburetor to see if you get a good strong flow of gas into a separate container held at the same height as the carburetor inlet.  If it flows a strong pencil sized stream, your problem isn't lack of fuel.

When you do a cold start, you should be adjusting the mixture toward "rich" to get it to start, but you need lean it out as the engine warms up. You are also pulling the knob to choke it when you crank, right?  You need to push the choke knob back in as soon as it begins to stumble.  You also may have to lean out the mixture by turning the knob toward lean. I forget which way is lean and which is rich on the knob in the cab (I sold my last Model A in 1951!), you'll have to ask someone who has a model A if you can't figure out which way to go to lean it out.

The spark should be all the way toward retard to start the engine, then advance it about half way as soon as it starts, and make fine adjustments from there as the engine warms up and as you begin to drive off.  More advance gives you more power, up to a point, but beyond that point, more advance will make the engine stumble and kick back, so make sure you are not over advancing it.

To check for a plugged exhaust, you need to remove the exhaust pipe right at the exhaust manifold, then start the engine. It will be outrageously loud, but keep it running long enough to determine whether or not this makes the problem go away.  (Better warn your neighbors before you do this!)

If none of this leads you to the answer, you are best advised to get a fellow member of the Model A club to come over and give you the benefit of his experience (you are a member of the club, right!?)

Good Luck with it

Dick