[carbking]

Enlarging the idle tubes may help or it may not; consider the "Law of Unintended Consequences" first.

If the idle now is fine, and the hesitation goes away when the engine is at normal temperature; then the idle may be too rich at normal operating temperature with more idle fuel.

By hooking up a choke, you can maintain existing calibration when hot, AND add additional fuel when cold.

In a different lifetime, when I actually had time to build carbs, built a number of the 455 2-barrel carbs for the dirt-track racers. NEVER had to open the idle tubes, but NEVER removed the choke. Because of having the choke butterfly to straighten eddy currents when the driver was off the throttle in the corners, and the fact we kept a functioning power system; the carbs we built had no hesitation when coming out of the corners, and drivers loved them.

The aluminum flywheel acts as a double edged sword, and not a lot of Pontiac folks use one; as Pontiac engines, mostly, are "torquer" engines. The mass of the cast flywheel helps the engine at lower RPM when the engine is cold.

As my 350 is built for RPM and NOT torque, and because of previous experience with aluminum flywheels on smaller displacement high revving engines; I installed one . The speed of change of RPM with the aluminum wheel is stunning. But as I posted earlier, it requires a choke for city driving, even when the ambient is 80 degrees F. until the engine is completely warmed up.

The 800 CFM I tried first, with electric choke, works well on Pontiac 400 and mild to medium 455's; but the choke went off too soon, and still had issues. With the manual choke, I can pull the choke out a quarter of the way at each stop sign for the first 20 minutes, then push it in once the car is moving again. Once the engine is warm, the choke is no longer needed. Oh, and I have a very wide ratio transmission, so the overall gear ratio in low gear is over 9.

And just for the record, while I know very few enthusiast have any interest in fuel economy; my OVERALL, with maybe 40 percent city driving, is better than 20 MPG. I never purchased stock in Shell Oil.

In short, can you modify that carb so no choke is necessary on the street? Probably. But the overall result may be less than satisfactory.

Any possibility you have a unmodified 2-barrel that you could throw on for a test? If so, wire the choke so that the butterfly is at about 75 degrees instead of 90. If the hesitation goes away when cold, you will then know what to do.

Lots of theory on this thread, but a single test might give us an answer, without doing any modifications to your existing carb.

Jon.