End Carb Throttle Plate Holes
 

Beginning in 1964 and through 1966 the end carb throttle plates have a .026" hole through them. I have asked this before, but still am not certain why engineers added this. I have been adding these holes on all Tri-Power end carb throttle plates for many years now.

My theory is that the small amount of airflow actually moves a tiny amount of fas from the end carb float bowls through the venturi cluster. This prevents the fuel in those carbs from developing sticky, varnishy deposits. This would be for drivers who seldom or never open the end carbs. The fuel in those carbs evaporates and leaves deposits in the float bowls.

Another possible reason for the holes may be to allow a very small amount of air flow into the intake manifold, exhausting any vapor and liquid fuel in the area above the throttle plates. If the vapor and liquid gas is not sucked into the intake, the liquid will seep into the intake and may affect hot starting.

Similarly, the gaskets between the throttle bases and the float bowl were modified to vent the area above the throttle plates to improve hot starting. This change was made in about 1963 to all three carbs.

Do any of you have theories on this?

I thought the holes were there to prevent vacuum from pulling the butterflies open in high vacuum situations where the carbs are closed.

The throttle body gaskets were vented to prevent or at least minimize stalling in city traffic during hot weather.

Jon

The very small holes in the red circle?

Yes .026" in diameter.

Makes sense the holes would 'vent' the slave carburetors especially if they were rarely used during driving

That makes sense. The small holes don't interfere with idle, but flow enough air to keep the throttle plates clear of gas. There is sometimes a small amount of fuel that collects on the end carb throttle plates.

Is there enough airflow to suck gas from the venturi cluster to keep fuel in the float bowls from becoming stagnant?

Maybe I'm wrong but that looks like the wrong gasket.

You are wrong. The vented base gasket was used on all '65 and '66 Tri-Power carbs. The theory was that there may be fuel on top of the throttle plates, causing difficult hot starts.

I use the vented gaskets on all Tri-power restorations I've done since about 1981,

Some look at the gasket and proclaim the venting causes a vacuum leak. But they need to consider that the vents are ON TOP of the throttle plates--no affect on vacuum.

My original post was a question on why the .026" holes were added to the end carb throttle plates.

I find it very hard to believe that the small .030" holes would draw fuel from the cluster.

If so, how much fuel would the much larger .055"-.081" holes in the throttle body on the center carburetor for cars with automatic transmissions pull?

Isn't it true that the vented gaskets vent excess vapors when the engine is off and that the holes in the throttle body draw in excess vapors left for combustion instead of clogging the throttle blades?

I imagine Pontiac started using sealed gaskets for the outer carburetors when they introduced the small holes in the throttle blades to avoid dirt being drawn into the venturi via the vented gasket.

Conclusion, for end carbs, no holes i blades, vented gasket.
Holes in blades, closed gasket.
Both vented gasket AND holes in blades, dirt in carbs.

FWIW