Do two simple tests.
First, do some heavy primary side pulls w/o the secondaries. Lug the engine, climb some grades, and speed up in high gear to make sure it has PLENTY of jet in it. If it pulls well and not nosing over, lackluster, flat, lacking power etc the jet size is fine.
Next set the APT at 3.5 turns and do some light load testing. Evaluate transition right off idle, speeding up with minimal throttle opening, etc.
Raise/lower the APT if/as needed for best throttle response, power, etc at the leanest setting.
It may take quite a bit of driving and a couple tanks of fuel to nail down the best APT setting.
IF you find yourself backing out the APT much more than 4-4.5 full turns you may need to go to a smaller primary rod. I'm not sure I had the full taper rods back then but a good option for the later carbs that used the shorter rods with .026" tips.
During all of this you can gander at your A/F meter but tune for best results, not any particular reading(s).
A well thought out engine build with optimum compression, tight quench, well chosen cam, adequate timing from the VA, etc will not want a lot of fuel to be happy.
Pontiac engines are very sensitive to quench distance, especially with factory iron heads on them. I've seen plenty of them run hot, overheat, and ping on pump gas when they shouldn't be simply because they had the pistons way down in the holes at TDC and/or thick head gaskets.
I will not assemble one here with more than .040" quench for any reason, even it tightening things up with decking/squaring and thinner head gaskets raises the compression.
Not paying attention to these things, decking, squaring, establishing tight quench, can not only cost the end user a LOT of power they can end up with other issues like running hot/overheating.
Take the average 350 SBC build. I get at least a dozen calls a week from folks who have just finished one up and wanting carb parts or carb work.
So I start asking questions, like what heads did you use?
What pistons and deck height?
Head gasket thickness?...etc...etc.
Most will say "stock" iron heads that were "ported", but no idea the casting numbers and 9 times out of 10 they will be 882 (door stops) with large 76cc chambers.
Deck height....not a CLUE, but likely .030" or more in the holes if they used a "rebuilder" set of pistons.
Head gasket thickness, not a CLUE, but for sure it was NOT the OEM .020" shim gaskets and probably .040-.060" thick instead.
So their engine instead of being 9.5 to 1 compression as their machinist told them which it would have been with .035" or so quench, flat top pistons and a little cut off the heads, it's probably closer to 8 to 8.5 to 1 compression......and they wonder why it doesn't idle well with their Comp XE or Thump-ya-muther cam in it and doesn't make chit for power either.
....continued
