Problem with SPF 1207

[Hal Copple]

In my 392 custom stroked Windsor, when i had it on a chassis dyno a year ago, the dyno operator showed me on the power curve where he could tell my secondary's were finally opening, i think about 4k rpm or so. He put in the lightest (white) spring in my vacuum attachement, and i picked up 40 !! horsepower, mostly in the mid range, and with the earlier opening of my secondary's, the "bump" in the power curve on the dyno graph disappeared.

I tweaked and chopped on that 750 vac Holley, cut off the choke tower, and recently put on a 750 Pro HP Holley, again with a vacuum secondary, and it gives noticably more power. But both carbs were seamless in their power deliveray.

I doubt your problem is ignition related, more likely fuel/air inadequacies. I ran and run now front 71 jets, and rear 80 (which is bit rich, but more protective against detonation). Power valve on my car is a 6.5. You may not be running enough air cleaner, these engines can be hindered by inadequate air flow from too small an air filter, especially one that is low, and makes it hard for the air to make such a sharp turn to go down into the primary side, what with the choke tower. As my speed shop guy reminds me, the primary has to flow as much as the seconary system!

My suggestion, is to check your timing, i ran best at 32 degrees total at 4000 + rpm, put on a bigger filter, i run a 14 inch diameter, 3 inch tall DROP BASE ! K&N, and put in the white secondary spring. My idle needle's seem to run best about 1 and 1/4 turn out in the front metering block.

Oh, on a 4160 series Holley, which is probably what you have, you have a rear metering plate, not rear jets, as you don't have a rear metering block, which i swapped out to on my carb, making it into a 4160 series Holley, so i could swap out rear jets easier. But when you do this, your hard chromed fuel line won't fit, as the rear metering block is 3/4 inches thick, and makes the carb a bit too long for the fuel line you have, i put on braided stainless steel to my car.

I don't think you need to swap out your rear metering plate, it will cost about $100 to change to a rear metering block with new fuel lines.

As for the MSD, i have mine in my engine compartment, on the passenger side footwell, although i do have it partially shielded from radiant heat with some aluminum-faced heat shielding. No problems, now at about 42K miles.

My car runs with the smoothness of a modern EFI engine, as do most of these cars, so i suggest you not embark on some long and complex road to a highly modified carb. Just do the secondary spring, and get the big drop base air filter. I have seen these cars gain as much as 75 horsepower with a switch to a big enough aircleaner.

keep us informed.