Choke pulloff

[PaulC]

What would be the symptoms of a defective choke pulloff?
I've been pondering if that might be the cause of my cold start engine dying after it starts unless you keep your foot on the accelerator.
Or is it just that the choke idle speed needs to be raised?
But again, once it's warmed up it runs well and restarts immediately.

[18Fiatsandcounting]

Coolant-driven choke or electric? Do you know what model carb you have? 32ADHA or 32ADFA perhaps?

Either way, if you remove the air cleaner and peer down into the carburetor and open the throttle by hand, you should see the choke plates snap close. You may have one choke plate or two, depending on the carburetor. If the engine is already warm, the choke plates may not snap all the way closed.

Have an assistant start the engine while you watch those choke plates. As soon as the engine fires, the choke plate(s) should move open slightly, perhaps 1/4 open. This is the choke unloader at work, and it lets enough air into the engine for it to run, once it starts. As the engine idles and warms up over 5 or 10 minutes, the choke plate(s) should slowly move to full vertical (fully open). Note that sometimes you have to blip the throttle periodically for the choke to continue to open.

If the choke plates stay fully closed when the engine first fires, the choke unloader is not working. That could be part of the problem, but it might also be that you don't have the fast idle speed adjusted correctly for when the choke is on.

-Bryan

[PaulC]

32ADFA with electric choke.
Will take a look at the suggestions next time out.

[PaulC]

Engine still cranks a bit to start but at least it doesn't die on startup like before when cold.
When I received this used carb (32ADFA) it was in pretty sorry shape so I rebuilt it and put all the adjustment screws back in their original positions. Since then it has always been a bugger to start and keep running until warmed up with having to continually blip the throttle to keep it running.

Ignition and gas all checked out ok so I started taking a look at the ADFA workbook for clues and made a few adjustments.

First I noted that the choke pull off plays an important part in cold running by opening the choke a bit after the engine starts. Also noted that it's operation requires a vacuum from the idle to activate it. Also noted that there is an adjustment screw that looks to adjust the movement of the diaphragm in the choke pull off.

So my reasoning was if the choke idle speed was not high enough to create enough vacuum and/or the pull off diaphragm wasn't moving far enough this feature would not be effective.

Based on this I adjusted the choke idle speed higher and screwed out the pull off adjustment so that the slotted end was even with the housing ( it was screwed in quite a bit before).

Yes, I realize this was changing two variables at once, but lo and behold, engine started on second try and kept running at a decently smooth high idle. A few more tweaks to the mixture and idle screws and it's never run better.

Now we'll see what happens on the next cold start.

[18Fiatsandcounting]

...but lo and behold, engine started on second try and kept running at a decently smooth high idle. A few more tweaks to the mixture and idle screws and it's never run better.

Sounds like progress, Paul! Yes, there is a fairly complex interplay between the idle speed screw, the idle mixture screw, the idle jet size, the choke unloader (pulloff), and the high idle speed cam adjustment when the choke is on. Over time, all of these need adjustment, and when all is working as it should, the system works fairly well.

When the choke is "on", the high idle speed should be around 1500 rpm. As the choke progressively shuts off, that speed will drop down to around 850 when the choke is fully off. Depending on your climate and altitude, you may need to adjust these a bit.

I've always just tinkered with the adjustments until it seemed best for the particular engine and climate. I've almost always had to pump the gas pedal a few times before cranking the engine. Doing that shoots some gas into the intake from the accelerator jet, which always seemed to help in starting. Sometimes it would stall out after a few seconds and I just repeated this process. Part of the fun of owning a car with 40 or 50 year old technology. Sometimes that's as good as it gets.

-Bryan

[PaulC]

My starting process is the same, but it's a whole lot better now.
The ADFA manual does mention the adjustment for the choke unloader but you need the elusive 3 part tool #4900 .
Guess my SWAG method was good enough.

[18Fiatsandcounting]

Guess my SWAG method was good enough.

That's what I'm thinking. I have seen this unloader adjustment screw, but I always just left it where it was. My assumption was that it was there to compensate for production variations amongst various carbs (or which engine they went on), but once it was set for a particular application, it was good forever. Not like the other carb adjustments which need periodic tweaking.

-Bryan

[PaulC]

Yes, that should be the last adjustment for that device.
Don't know what car the carb came from just that it was sold as parts only. But really it just needed a good overhaul.