Stop Stall

A

ampico-kid

Senior Member
Long time member, first time posting. This topic has probably been beaten to death, but it's a problem I never had with my 30 Coupe, so I never paid much attention to the subject. I've now taken the plunge and gotten a 30 Town Sedan to keep my Coupe company. The car is in great shape, but I now have that miserable stall when you stop issue. The carburetor that was on the car was in sorry shape, and the car would stall every time you stepped hard on the brake. I decided to upgrade and put a new Zenith-1 carb on the car assuming that would eliminate a whole batch of problems. Long story short....the new carb didn't solve the stall when you brake hard problem. I also find that the idle mixture screw has no effect on the idle quality (which isn't very good).

After doing a lot of reading on the subject I'm now thinking the carb and float level (apparently a common cause of this problem) are not the issue since both the old and new carburetors perform the same. That points to a vacuum leak in the intake manifold. Visually the manifold looks fine, although I can only see part of it. I'm hoping that the problem might be the gasket from manifold to engine block. Although I haven't tried it yet, I'm thinking about spraying some starting fluid near the gasket to see if that has any affect on the idle speed.

Just wondering what you all might think about this situation?

Thanks. Bob
 
Last edited:
It sounds like a clog in the carburetors internal circuitry possibly. It seems like a vacuum leak would respond to enriching the mixture? You can try running some cleaner through by removing the screw spraying some cleaner in replace the screw a little compressed air could help as well.

Using starting fluid or even brake cleaner can help you diagnose a possible vacuum leak in the intake. don't spray too much as it could be pulled into the carb and give you a false indication.
 
In another thread the solution to the stop stall was to raise the fuel level in the carburetor. However, check for vacuum leaks first.
 
We had the same stop stall problem with our '30 coupe. Found that braking hard in reverse caused no stall. Raised the float level and the stop stall was over.
 
The stall issue was cured in 32, when the B engine was introduced “the new and improved 4 cylinder” set the float port and starboard, instead of fore and aft on the A
 
You have two carbs that have issues. Just that simple. I do agree make sure you have a good tight intake, no leaks at vacuum to wiper. And get the carb issues fixed . Not always easy. You might need someone who is very schooled at carbs around you to assist. You have more than a float level issue if your idle screw doesn’t do anything.
Larry
 
X2 on post #3. Check for air leaks at the throttle plate, wiper connections and all manifold connections. Cracks in the intake manifold too. Remove the throttle rod and shake the throttle at the throttle plate. If it moves side to side, you have a leak there. It will need and oversized shaft or a bushing and a standard shaft.

Our ’31 coupe (Little Bug Eye) has a Bert's rebuilt Zenith carb on her. Her driving history is clouded by a fresh motor that was breaking in and a new Model A owner. Now, after 8500 miles she idles nicely after warm up and no longer stalls at a stop. Still, I glance at the ammeter as we come to a stop, especially at specific corners where during break in, she did die. Her ammeter would flicker widely, warning of an imminent stall. A quick adjustment of the hand throttle preempted this. Little Bug’s stalling was corrected by resetting the base idle speed with an idle air adjustment screw setting at ~ 1-1/4 turns.

I have a handheld digital tachometer that connects to the coil. The ending idle rpm was set to 470 at 25% spark advance. If your idle speed is too high, the GAV has too much authority as the throttle plate is further open.
 
Last edited:
OK....there's a lot to unpack here. First....the carburetor that I used to replace the original is a brand new Zenith-1.....not a rebuild, but one of the brand new ones. I purchased one of these newly manufactured Zeniths for my coupe several years ago and it's worked flawlessly since I installed it. Instead of having the original carb. on this new car rebuilt and hoping it was done correctly, I decided to bite the bullet and buy and install another of the new Zeniths, which I did. I would think that the new carburetor is not part of the problem equation since it's reacting much like the original old carburetor. I'd find it hard to believe BOTH carburetors would have the float level set wrong. And the throttle plate feels very secure and as tight as it should be to allow for easy movement on this new carb. This all leads me to suspect a leak on the intake manifold which I just checked with starting fluid. I idled the engine down as slow as I could without stalling, and sprayed the starting fluid around the intake to block connections. Spraying around the front port had no effect, but spraying the rear seemed to make the engine run smoother for about 20 to 30 seconds. I repeated it several times to be sure, and the results were consistent. So....I assume that what I've discovered is an air leak on the intake manifold.....hopefully just the gasket. Would you all agree?

Thanks for all of the input and advice.
 
As my ex wife once, and only once, said, " I do."

I have the gasket that is two gaskets and looks like cardboard on Little Bug, but I have the copper clad one in reserve waiting for the failure.

I think yore on to it.... rootin' fer ya.
 
Rob Doe said:
As my ex wife once, and only once, said, " I do."

I have the gasket that is two gaskets and looks like cardboard on Little Bug, but I have the copper clad one in reserve waiting for the failure.

I think yore on to it.... rootin' fer ya.
Click to expand...

Will let you all know how it turns out.....either way. Thanks!!!
 
Chuck Sea/Tac said:
Where do you set the gav once it’s running up to temperature?
Click to expand...


I think it depends on the car. I open mine 1/2 to start, and I close it all the way when it starts to warm. The plugs are tan like they should be; so, I don’t think it’s running rich or lean.


Sent from my iPhone using Tapatalk
 
This slide may help you understand what goes on in the carburetor when the engine stalls.
 

Attachments

  • Engine Stalls178kb.jpg
    Engine Stalls178kb.jpg
    59.1 KB · Views: 78
ampico-kid said:
OK....there's a lot to unpack here. First....the carburetor that I used to replace the original is a brand new Zenith-1.....not a rebuild, but one of the brand new ones. I purchased one of these newly manufactured Zeniths for my coupe several years ago and it's worked flawlessly since I installed it. Instead of having the original carb. on this new car rebuilt and hoping it was done correctly, I decided to bite the bullet and buy and install another of the new Zeniths, which I did. I would think that the new carburetor is not part of the problem equation since it's reacting much like the original old carburetor. I'd find it hard to believe BOTH carburetors would have the float level set wrong. And the throttle plate feels very secure and as tight as it should be to allow for easy movement on this new carb. This all leads me to suspect a leak on the intake manifold which I just checked with starting fluid. I idled the engine down as slow as I could without stalling, and sprayed the starting fluid around the intake to block connections. Spraying around the front port had no effect, but spraying the rear seemed to make the engine run smoother for about 20 to 30 seconds. I repeated it several times to be sure, and the results were consistent. So....I assume that what I've discovered is an air leak on the intake manifold.....hopefully just the gasket. Would you all agree?

Thanks for all of the input and advice.
Click to expand...


I can appreciate you comment on the new carbs but from my experience which is more than the average beat most of the new carbs have issues. Not always the same but I’ve only ever seen one so we’ll from the start without having to correct issues.
Everyone thinks new is ok but not always the case. Have done hundreds of carbs so just my experience…. You do have to remove and get your manifold surfaced and install a new copper or steel clad gasket .
 
Chuck Sea/Tac said:
Where do you set the gav once it’s running up to temperature?
Click to expand...

Have only had the car for two weeks, and haven't run it out on the road long enough or hard enough to bring it up to a normal running temperature. With the stop/stall issue in the forefront of the problem list, I haven't played with the GAV other than to get the car started and then open it up a bit more.
 
larrys40 said:
I can appreciate you comment on the new carbs but from my experience which is more than the average beat most of the new carbs have issues. Not always the same but I’ve only ever seen one so we’ll from the start without having to correct issues.
Everyone thinks new is ok but not always the case. Have done hundreds of carbs so just my experience…. You do have to remove and get your manifold surfaced and install a new copper or steel clad gasket .
Click to expand...

Thanks for your reply/comment. I'm thinking I may just pull the carb off of my other A and install it on the Town Sedan and see what happens. It's a known excellent working carb, so it would resolve any doubts about float levels or air leaks or whatever.
 
You must log in or register to reply here.
Back
Top