<VV> '69 engine misfire?

[Michael Kovacs]

'69 110 PG 172,000 miles, never had heads off, doesn't smoke or use excessive oil.  Starts instantly. 



 Problem is a slight back fire when cruising. This is a mild series of pops through the carb(s) and a minor loss of power (to be expected).  A  stab of the gas will usually bring a moment of hesitation than normal power. The carbs were rebuilt by me about 2,000 miles ago due to tired accelerator pumps, they do squirt very well now.

 It has a protonics ignition installed years ago. It seems like a lean mixture to me, but how? The manifolds are from an non smog engine and the AIR was removed by PO 30 years ago. I've had this car since the mid 70's.

 I can check almost anything, but with this 20 degree weather, I'd rather concentrate on the most obvious. I drive it 20 miles to work with no other symptoms, but it seems much better when hot.
 MIKE KOVACS