Dead spot while accelerating

[Burlsube]

My IIa seems to have developed a sputter under hard acceleration. It will sputter for a few seconds, then it seems to surge and even out. It only happens on hard acceleration, if i were to gently accelerating or gradually increase the speed then there is no issue.

I am running a Zenith carb. I recently timed and tuned everything. Before I start tinkering I was wondering where I should I start.

[albersj51]

Have you looked at fuel delivery? Maybe a clogged filter or blocked pick up tube? maybe crap in the sediment bowl (assuming mechanical pump) or crud in the carb blocking the main jet?

[Terrys]

Is the accelerator pump jet clogged? Take the horn off the top of the carb, look down and see if it 'squirts" when you open the throttle.
Next I'd check the vacuum advance. Both are the main reasons for hesitation on acceleration.