Why does my engine die when stopping?

[Pat Martone]

My engine dies on the road when stopping, however when running the car in the driveway while parked and gunning the engine, it does not die but keeps idling.
This problem happens with 2 different carburetors, with one of them being a brand new $400 carburetor from Bratton's.
I welcome your advice; thanks!

[Gary WA]

Maybe crud in the tank,or if you have a glass sediment bowl the screen may be plugged in the top, cast iron sediment bowl same crud in it. ensure you have good gas flow to the carb. possibly a short in brake switch?

[steve s]

I have read conflicting explanations of why this happens, but they usually involve the carb float pivoting on an axle that is crosswise to the direction of travel:

1. During a hard stop, the gasoline rolls forward, the float drops, more gas enters the bowl giving too rich a mixture.

2. The gas rolls forward, lowering the fuel level over the exit jets giving too lean a mixture.

3. The gas rolls forward, then sloshes back, over-enriching the mixture.

Nonetheless, many folks don't have the problem. They will be telling you to either raise or lower your float level. You can also try fiddling with the GAV.

The B carb has the float pivoting on an axle parallel to travel, and some have an anti-slosh baffle. Personally, the problem was solved for me by going to the new Zenith 13922 (from a $400 new Zenith 1) but you're probably not up for another new carb purchase for a while.

Steve

[pat in Santa Cruz]

a vacuum leak will do that as well as an incorrectly adjusted float. A common leak is a loose throttle shaft. Since you tried 2 carbs, it could be the intake manifold or gaskets.

[BILL WILLIAMSON]

Very typical idiosyncrcy with many Zeniths On HARD stops! ( gas sloshes fore and aft and momentarily floods/starves normal mixture ) On hard tops, just pull throttle lever Down a couple or so clicks 'til idle stabilizes! This ain't your modern car! If your float level is correct, don't diddle with it, as changing it will NOT overcome this idle thing! Bill W.

[BILL WILLIAMSON]

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Originally Posted by pat in Santa Cruz

a vacuum leak will do that as well as an incorrectly adjusted float. A common leak is a loose throttle shaft. Since you tried 2 carbs, it could be the intake manifold or gaskets.

His comments said it idled good in the driveway & when reving, so that rules out vacuum leaks. Bill W.

[ford1]

when in the drive way idling will the engine die when brakes are applied, if not that eliminates the brake switch, does the engine stumble or just die when you stop, if it stumbles to much fuel, if it just dies no fuel

[Pat Martone]

The engine does not die when the brakes are applied.
I do not think it is a float issue since 2 different carburetors are still resulting in the engine stalling-out at stops (and one carb is brand new), unless I give it a little gas and release the pedal and somehow the carb "recovers" and will continue to idle just fine until the light turns green and I can proceed.
When running the car while parked in the driveway, I can gun the engine and release the accelerator quickly without the engine dying, but when I actually drive the car and slow down or stop (while in neutral) the engine dies.
Maybe my car is not a "driver" after all?
(But, it is certainly not a show car either!)
Again, I welcome your advice; thank you.

[Barry B./ Ma.]

I notice that a little in my coupe so before coming to a stop I richen the GAV valve about 1/4 turn and it doesn't try to stall out.

[ericr]

has Pat actually tested the float level? I certainly have purchased "rebuilt" carbs that had this problem and it was the float level being too high.

[Pat Martone]

Yes, float level is 5/8" on both carburetors.
But, I appreciate you asking!

[Patrick L.]

So it seems as though this only happens when in neutral ?? It doesn't do it when in gear ??
How is the idle speed ?? Maybe try raising it a bit.. Have you played with the GAV and idle mixture?? I think I would try those before playing with float level, if that doesn't work, then I guess I'd change the float level about 1/16"..

[Ronnie Lawson]

I read an article in the Chicago Service Letters 1930-31. The service letters were sent out by Ford Motor Company to authorized Ford dealers for the cars and trucks.
Recently complaints have been received of difficulty experienced in adjusting carburetors on new cars for idling speeds, excessive gas consumption and motors stalling when stopping cars at street intersections.
In most cases this happens on cars drive 500 miles or less. As motors now being built have highly polished crankshaft main bearings, this is not sufficient mileage to limber them up. In fact so little wear takes place with these polished bearings, it sometimes requires considerably more driving before the motor is well broken in.
The very best results cannot be obtained until these motors have reached the point where the bearings produce the least amount of friction. Then if the carburetor is carefully adjusted, and the motor is timed accurately, with spark plugs gaps set at .027 to .030 and distributor points properly spaced, at .018 to .020, they will attain their maximum efficiency and operate the most economically.
Note the spark plugs gaps and point setting. I have always heard that the plugs should be set at .035 for a stock head and .030 for a high compression head and the points set to .018 to .022.

[Pat Martone]

Yes, with both carbs, I have adjusted GAV, idle screw, and fuel mixture screw.
The timing is correct, points gap is correct, and spark plug gap is correct. I believe I have a high compression head because I measured 70-71 psi compression in all 4 cylinders.
I previously indicated it dies when approaching a stop in neutral, because of course the engine would die if it were in gear when I stopped.
Any other suggestions?
Thanks.

[steve s]

Originally Posted by Pat Martone

...
I previously indicated it dies when approaching a stop in neutral, because of course the engine would die if it were in gear when I stopped.
Any other suggestions?
Thanks.

Pat,

This might be your clue--don't approach a stop in neutral: Do not step on the clutch until the very last moment. I have found that this technique helps a lot. The motor won't stall as long as the movement of the car is keeping it turning. Providing an extra second or two for the sloshing and whatever else is going on in there to sort itself out can make a big difference. That, and, as others suggested, stepping up the idle speed a bit will definitely help--save showing off your super slow idle for driveway moments.

Steve

[Pat Martone]

Steve,
Thank you for the advice; I have tried keeping the car in gear as long as possible and raising the idle, but the engine still dies.
This is very frustrating since I think I've tried everything to resolve this problem.

[pat in Santa Cruz]

Originally Posted by BILL WILLIAMSON

His comments said it idled good in the driveway & when reving, so that rules out vacuum leaks. Bill W.

not necessarily. It takes a lot of vacuum to initially draw the fuel up the idle tube. When stopping the car, the carburetor must shift fuel supply from the main jet circuit to the idle jet circuit. A small leak near the idle jet, like a loose throttle shaft, leaking gasket or crack in the vacuum port of the manifold, will delay that long enough to kill the engine. Once the fuel gets to the orifice, the siphoning effect draws enough fuel to allow a good idle. I've seen this too many times to ignore checking it out. I would not rule out a poorly seated idle air mix screw either. But since Pat has a new "rebuilt" carburetor, its a slim possibility. The only rebuilt carburetors I have installed with never a problem were Chris Pelikan's. Those from some other sources, even some well known ones, have occasionally performed exactly as Pat describes..

[HoarseWhisperer]

Originally Posted by BILL WILLIAMSON

His comments said it idled good in the driveway & when reving, so that rules out vacuum leaks. Bill W.

I had a different experience. Although they would idle good, two carbs would stall at hard stops.

Replacing the throttle shafts resulted in no more stalling at stops. Small vacuum leaks.

[msmaron]

Check the first basic thing..What are the points set at and did they close
Next Check for rust or junk clogging the carb
Re-Set timing and air/gas mixture dial on carb
Check for vacuum leak at the vacuum line at the fire wall,
Check same at Manifold gaskets and nuts

Good Luck!

[joltesvig]

My 31 Coupe does the same thing but only on those quick stops like when I'm going down hill and have to get stopped quickly. I have checked the float level, vacuum leaks. Pulling down the throttle lever a little to bring the idle up before she dies has worked well for me. I'll also do another check for vacuum leaks...is that a visual check or can vacuum be checked with a gage?