warm model A motor begins to stutter

S

sojoanfr

Junior Member
I hope, someone has an idea.

After changing the regulator the motor begins to stutter when it gets warm.
The electrical system is a 12V system. The regulator was changed because the regulation of voltage didn't still work. I checked timing, distributor, checked and cleaned all gaps/contacts.
I checked the fuel mixture.
I checked sparks.
The Motor is starting perfect and runs good.
But when the motor gets warm after driving only 1 or 2 km,
the problem begins.
Checking the motor, valves work good, and I think gasket is not burned.
In my opinion the intake gets very hot. when touching the throttle at carburetor it is so hot that is near to burn the fingers.
I hope someone knows the problem.
Thank you for ideas.
 
I would check ignition timing first...even if you already checked it once....

Does the coolant/radiator get hot?

What part of the world are you in?
 
I checked timing already 5 or 6 times. First piston was in upper position and timing pin was fitting in gear hole.
But I will check it again.
I'am from Germany/Hessen.
 
Sometimes if the fuel cap is not venting properly the fuel flow will be restricted. Maybe resulting in a lean mixture.

Try loosening or removing the cap.....

Have you had the car very long?
 
sojoanfr,

Since this is your second post, I assume you are new to the Barn, so welcome. First of all, when you say "regulator" do you mean "distributor"?

It could be that the fuel mixture is too rich when the engine warms up, have you tried adjusting the GAV (Gas Adjustment Valve)? The gas mixture may be too rich. For example, when you start up the engine do you have it at 1 turn and then when it warms Up have you tried to close the GAV slowly to see if if runs more smoothly?

David Serrano
 
Thanks for all informations

fuel flow was good, shut off open there was a good flow out of the plastics filter

idle mixture is open 1.5 to 2 turns

GAV turning: there is no reaction, my impression

May be the adjusting needle is blocked? but choke works
The next step can be to check carburetor.

May be there is a problem with malfunction condenser?
Can a malfunction condenser cause backdraft and/or overheating intake.
Or the heat can be caused from very/to hot exhaust. Exhaust has no leakages.
The problem is, still very hot intake and carburetor and stuttering motor under load.

I think,
i will do one step to the other.
To change the condenser is quick and easy.
Then next step is checking the carburetor.
 
You've checked the timing, however it sure sounds like a timing issue. Have you tried running it at night? If so you'll see the manifold turn almost cherry. Check your timing procedure, make sure your timing on the right slope of the lobe and account for backlash. I would not run it much when its getting that hot. Good way to destroy it.
 
Recheck that timing. Lots of You Tube videos on setting the timing on a Model A. Some use a "test light" some a NuRex wrench. There's even one on there where the presenter has such a foul mouth that I had to turn it off. Sad.
Keep us posted, and enjoy the adventure, Chap
 
I maintain a car that behaves similarly; engine was "newly rebuilt". I found that getting everything perfect in timing, carburetion, and distributor function (as tested in another vehicle) helped but it still boils gas in the carb when hot and sounds rough when idling. A high compression head improved the situation and makes the car driveable. Careful adjustment of valve gaps helped slightly. I suspect that the exhaust manifold is paper thin and a great heat radiator to the carb but ultimately I think it has a poorly reground camshaft or worn original that makes it a dog.
 
Vapor lock/percolation was my first thought.

1. Keep spark advanced as much as possible. Late spark can send still-burning gas into the exhaust manifold. Energy is wasted heating the pipes instead of pushing the pistons.

2. Check muffler/tailpipe for restrictions. Pressure buildup in the manifold prevents proper expansion cooling of the compressed gas as it passes into the lower pressure chamber.
 
sojoanfr said:
I hope, someone has an idea.

After changing the regulator the motor begins to stutter when it gets warm.
The electrical system is a 12V system. The regulator was changed because the regulation of voltage didn't still work. I checked timing, distributor, checked and cleaned all gaps/contacts.
I checked the fuel mixture.
I checked sparks.
The Motor is starting perfect and runs good.
But when the motor gets warm after driving only 1 or 2 km,
the problem begins.
Checking the motor, valves work good, and I think gasket is not burned.
In my opinion the intake gets very hot. when touching the throttle at carburetor it is so hot that is near to burn the fingers.
I hope someone knows the problem.
Thank you for ideas.
Click to expand...

Are you running a 12 volt coil or a 6 volt coil
 
sojoanfr said:
I hope, someone has an idea.

After changing the regulator the motor begins to stutter when it gets warm.
The electrical system is a 12V system. The regulator was changed because the regulation of voltage didn't still work. I checked timing, distributor, checked and cleaned all gaps/contacts.
I checked the fuel mixture.
I checked sparks.
The Motor is starting perfect and runs good.
But when the motor gets warm after driving only 1 or 2 km,
the problem begins.
Checking the motor, valves work good, and I think gasket is not burned.
In my opinion the intake gets very hot. when touching the throttle at carburetor it is so hot that is near to burn the fingers.
I hope someone knows the problem.
Thank you for ideas.
Click to expand...

You say it gets hot:

You say it gets hot in a distance of only 1 or 2 clicks?

Basic things first before replacing parts.

Are you advancing the spark to about 50% OF SCALE after starting and while driving or are you running with it retarded (all the way up)?
 
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A video with sound of motor running might reveal what is going on.

Video of spark lever position.

If you are running car with "winter" gas and temperature is higher than 70 to 100 F.

Gas could be boiling in carb and cause the "stuttering".

Even more so if spark is retarded.
 
Last edited:
sojoanfr said:
Thanks for all informations

fuel flow was good, shut off open there was a good flow out of the plastics filter
....
Click to expand...

Remove that filter! They work fine for some people but not for others. Flow tests in driveway are not reliable indicator of what happens going down the road. I suspect multiple problems are in play, and especially agree with all who accuse timing. Even if it's set right, you still need to advance the spark after starting--do you?? (someone else asked this first)

Another straw to grasp at, make sure you don't have a Model B timing gear cover.

Too rich fuel mixture will not cause overheating; just the opposite. Opening the GAV is a quicky way to cool combustion a bit, as the extra heat of vaporization required helps a bit.
 
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