[Chaplin]

Mr Fixit
Here's the interesting thing. The carb is a stock 3310 that had 72 primaries and a 6.5 power valve. At idle, the engine was running very rich and it had a bit of a stumble/bog between 1800 and 2100. I measured the manifold vacuum and it was only 5"/hg at idle (about 950) and 8"/hg at 1100, and 16" at 2200. I called up Holley and they said to first change the power valve to a 2.5, drive it and then if it's still rich, change the jets.

Well, I changed the pv to a 2.5 and drove it around for a while. The stumble around 2000 rpm was much improved, but a new problem developed. When you are cruising in third gear at 2500 or so and then quickly push the gas pedal down, there is now hesitation in the 2800-3000 rpm range that was not there before-it almost sounds like a lean miss. If you gently roll on the throttle, there is no hesitation.

I need to get some longer tubing on my vacuum gauge so I can drive around and see what the vacuum readings are on the road, but I had the following thought: Is it possible that when I am cruising and when the vacuum is highest, the vacuum does not drop enough to activate the 2.5 pv causing a lean condition?

What do you think? And a smaller duration cam may be in the future . . .