Cranky carb ? (Zenith )

Special Coupe Frank

Special Coupe Frank

Well-known member
Took my '28 for a long drive today (40-some miles), after draining the water and installing 50-50 anti-freeze.

About five miles into my trip ( all urban / suburban driving, plenty of stop-signs and traffic lights), I noticed that the car would start to "pop" in the exhaust about half-way down a hill while coasting with the throttle closed, and it would stall at each and every stop, unless I set the hand throttle up to about 1000 RPM.

Didn't seem to matter which way I set the GAV, it did pop worse if I retarded the spark all the way.

There were no issues with fuel starvation / pulling hills. It did not pop or cough when I stepped on the accelerator.

I did notice that the popping while coasting would go away if I pulled the choke slightly.

All of this suggests a clogged idle jet / passage.

When I finally got home, I got under the hood and tried to adjust the idle needle to get it to idle at its normal speed ( where it has run just fine for 11 months / 5000 miles).

If I closed the idle needle completely, it would almost idle down; if I opened the needle even 1/2 turn, it would stall.

I removed that needle completely, and found the tip coated in sooty black... I wiped that off and re-installed & adjusted, but no improvement.

What would cause the idle needle to get sooted-up ?

Thanks in advance...

SC Frank

( no air-maze or other filter, BTW.)
 
I have found over the years that if you are running summer gas in temperatures hovering near the freezing mark with carburetted engines that they invariably want to stumble during idle speeds or even stop running completely. Gasolines are seasonally adjusted at the refineries, summer gasoline does not contain enough vaporizing agent for decent cold weather operation.
 
I 've been running 10% ethanated gas since getting the car a year ago; this is the first issue I 've had with the carb.

Car is a regular driver, going through a tank every two weeks or so; I'm pretty sure I'm running winter-blend.

Also, car has a 160 thermostat and consistently runs 160*.
 
Maybe you were getting carb icing. It can happen at the right temp. I used to get it when I drove a model A pickup to work years ago.
 
George Miller said:
Maybe you were getting carb icing. It can happen at the right temp. I used to get it when I drove a model A pickup to work years ago.
Click to expand...

I thought about that, but when I pulled over and looked under the hood for leaky float, or other obvious issues, I didn't see any frost on the bowl.

I have had occasional issues with carb icing with other vehicles, but usually when running at higher speeds, when air-flow through the carb is greater...
 
Special Coupe Frank said:
I thought about that, but when I pulled over and looked under the hood for leaky float, or other obvious issues, I didn't see any frost on the bowl.

I have had occasional issues with carb icing with other vehicles, but usually when running at higher speeds, when air-flow through the carb is greater...
Click to expand...

You might not see the ice, it can be inside carb from the cold moist air speeding up going through the carb. Does it run ok after it sets for a while.
 
I was going to suggest setting the points, but Mitch beat me to it. Also, if you will give that ethanol about a jigger or so of Marvel Mystery oil (about two ounces) per tank it will help. I give my AA a dose every time I get fuel. The gasoline here in metro Atlanta almost has more additives than petrol.

JW
 
Frank, I had a recent similar experience with my 30 doodlebug, would only run if I held the choke part way, it progressively got worse and ended up being an air leak in the manifold. On taking off the carburetor I noticed a cracked mounting ear. I put on another manifold with new gaskets and runs ok now.
 
This sounds like a classic vaccum leak on the top plate of the carb. One of the plugs is leaking. Take a punch and give the plug a couple of light taps.This should reseat it.
Then it could just be a intake gasket leaking.
My A's when cold,you pull the choke and turn the motor about 1/2 a turn then push it back in.They fire up and start to idle right away. I run E-10 gas
Wick
 
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