Air, Fuel, Spark. From your description it sounds like Air and Spark are okay...So, when was the last time the fuel filter was changed? 

> On Dec 12, 2018, at 3:58 PM, al sinclair <alvanagon@GMAIL.COM> wrote:
> 
> Please help suggest a cause of a new problem in 1981 Westie (aircooled),
> automatic not stick shift.
> 
> Occasionally, a few times a day, there's no response from the engine when
> pushing the accelerator pedal to accelerate from stationary. The pedal
> moves normally, and the sound of the engine changes so I think the throttle
> opens, but there's no change from idle, no increase of power for at least
> several seconds. Then the engine behaves totally normally. I've begun
> pumping the pedal when this happens but I'm unsure if it makes any
> difference.
> 
> The engine was rebuilt a couple of years back (lovely job by Greg Tuttle,
> installed by Fred's Garage, runs like a dream) maybe 10,000 miles ago. It's
> had oil changes but little else since then.
> 
> Any ideas how to identify the cause will be much appreciated. The problem
> isn't reproducible on demand, it only happens now and then - and can be
> scary if I'm pulling out across the road.
> 
> Thanks
> Alan