i got my distributor recurved and converted to crane HI-6 and in the instructions from Carmen it says to run 14 degrees initial timing and to run ported vacuum to the vacuum advance. my carburator only has a manifold vacuum port and when i run 14 initial and hook up the vacuum advance to the vacuum port i get a total of 28-30 degrees advance at 650 rpm..my engine doesnt seem to like this and doesnt idle as well as it could. what are my options? no vacuum advance... leave it as is and live with it? if i drop my initial setting it helps but then i'll lose my some of my total advance.. Bob
You could have the centrifugal curve "opened up" to provide more centrifugal, then back off the initial timing. Then you'd have the same total timing and still be vacuum-advance-friendly connected to manifold vacuum.
my centrifugal starts at 1100 and is all in by 3000 rpm with 20 degrees of mechanical advance and 14 initial for a total of 34 degrees
how much total advance would it be if the vacuum advance were working correctly on the ported vacuum? You are stuck unless you recurve the mechanical for the desired total timing w/o to ported vacuum or no vacuum advance at all. I will guess that Carmen stuck with the ported vacuum method for a reason and would try best to keep to what he recommended or call and ask him. He might have the recipe handy for "plan B" Are you running a Q-jet or AFB? Are you sure you don't have a ported vacuum or are your throttle blades opened too far at an idle because of your cam?
Adam Carmen rebuilt my carb. it's a stock 65 GS carb. engine runs nicely at 650 rpm in park and just a tad rougher with the vacuum advance connected. according to the sheet he sent it takes 6" of vacuum to start the advance with 14 degrees of vacuum advance at 11" of vacuum. there is no ported vacuum port on my 65 afb carb. Bob
Hm, that's odd that he would direct you to hook it up on something that doesn't exist on that car.... It's an easy buck for me to pass, but I have no doubt that Carmen is the the one to ask so that you get the best performance out of it. After all, he is Mr. Nailhead; even if he is in Tonawanda NY, the birthplace to all the BB Chevies
There is no ported vacuum because the 65's ran with full manifold vacuum advance. They typically had initial timing of 2*, and the stock cannister supplied 14-18* of advance, so they idled at around 20*, which is ideal. With 34* total + 14* of vacuum advance, that's 48*. seems a bit high to me. I would limit the vacuum advance to 8-10* maximum. That will give you 42-44*, which should be ideal. Then, with 14* initial, you could idle with full manifold vacuum, at 22-24*, which should be better. It's easy to limit the stock cannisters. Just make a block off plate.
I had the same problem with hte rough idle on manifold vacuum, and IgnitionMan steered me in the right direction with Larry's picture there. Solved the problem and the car ran smoother than I had ever felt it run after that. Listen to the Wizard!:beer
