Stalling at idle

31 Woody

31 Woody

Senior Member
I finally have my Cabbie licensed and have had it out on the road. Unfortunately, there is a stalling issue. As we slow down or as the idle lowers it does sometimes stall. I was initially running a Tillotson—which was painful on starting, but ran good other than the stalling.

The Tillotson was difficult when cold starting. It took an excessive amount of choking and cranking, but then it would start and run. Once warm, it didn’t want to start unless rolling and popping the clutch. Even the slightest roll, you could pop the clutch and it would fire up. Cranking while warm, best to wait a few minutes, then try.

Tonight I switched to a B carb, it starts easier even after warming up, but stalls even more frequently if idled down too far. It started right off with some minor choking. When warm, a small bit of choke and it fired right up. If the idle was kept a bit high, it seemed OK but I did not go for a drive so I don’t know how it would bee over some more time.

Both carbs have been very thoroughly cleaned and reassembled with the basic new parts (gaskets, float valve, washers, etc). I don’t think there is a timing issue, but it could be a weak spark while cranking issue combined with a carb idle circuit issue (on both carbs)…but help?
 
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Please don’t take this the wrong way but there are so many threads on this subject that I don’t think I could do you service by attempting to answer you. Please do a search for “Stalling at idle” or “Stalling when coming to a stop”. Lots of great information on Ford Barn already about this topic.
 
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Just my two pennyworth...since it's still playing up with a substitute carb I'd start suspecting that it may not be carb related but possiblly the ignition circuit.:(
 
Measure the voltage at the terminal on the starter switch with respect to ground when cranking the engine over with the ignition off. If lower than 4.5 volts (or 9 volts) check the ground connection for the battery and make sure you have a ground connection to the engine (a transmission bolt). Make sure the connections at the battery terminals are clean and shiny metallic.

Here is a good site for the Zenith carburetor for the Model A. Not the carburetors you are using but the principles are the same: https://modela.org/default.html
 
If you have a safety fuse mounted on the starter check to see that the prongs that squeeze the ends of the fuse aren’t loose.
If they don’t grip the fuse tightly it will cause weak spark and stalling at stops like your what your experiencing.
 
As others have said, I suspect an electrical or ignition issue.

In addition to the others' suggestions, check your coil polarity. If backwards, it gives a weak spark, which can result in hard starting, stalling, etc.

You should not have to choke a warm engine.
 
Jim/GA said:
As others have said, I suspect an electrical or ignition issue.

In addition to the others' suggestions, check your coil polarity. If backwards, it gives a weak spark, which can result in hard starting, stalling, etc.

You should not have to choke a warm engine.
Click to expand...

Interesting—the coil and every bit of wiring was touched as I put this together. I really wasn’t sure if I had the coiled connected correctly or not. I am going to look at that again.

Thanks everyone.
 
Can you give a more exact description of the problem? You're saying the engine stalls if you lower the idle setting too far? Have you adjusted the idle mix on each carb?

Reversed coil polarity is not the problem. Reversed polarity will only decrease maximum spark voltage by 15%, and at idle you're not hitting the limits of the coil's abilities anyway. Don't waste your time.
 
Your symptoms (hard starting, stalling) are occurring at times when the manifold vacuum is, or should be, at it's highest. You didn't mention if adjusting the GAV caused any changes but I'm suspecting a lean condition caused by a vacuum leak.
 
Go old school....... You can check ignition coil polarity with a pencil by holding its graphite tip in the spark gap between a disconnected spark plug wire and the plug (or ground) while cranking the engine; a sharp, bright flare towards the spark plug (or ground) means correct polarity, while a duller flare towards the coil wire indicates reversed polarity, requiring you to switch the low-voltage (primary) coil wires.
 

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