For a streeter; that's all I know about:
All well and good, but modern carbs have the transfer slots engineered to run with the ported spark.
On street engines, if you try and run NON-ported spark, and simultaneously have the timing cranked, almost invariably the throttle blades end up too low on the transfers, and you crank the mixture screws out to compensate. Ok great it idles.
Then you put it into gear, and airflow falters and the engine throws a hissy-fit. If you manage to keep it running, then you get a tip-in stumble as the transfers come on line.
So then in desperation you start throwing timing at it, and the idle speed goes up. And then you reduce the idle speed with the speed-screw; Making it worse; probably again.
The thing for a newbe to keep in mind is that the idle fueling is determined by the 1-2 punch of transfer slots plus the idle trimmers. Those mixture screws are trimmers for making the engine rich enough to idle on.They are not there for the engine to idle on by themselves.
The lowspeed circuit is actually the transfer slots, trimmed by the mixture screws.
So if at idle your mixture screws are ineffective, then the transfers are doing all the work.
But if the mixture screws are out to double their mid-point, then the transfers are not supplying enough.
At idle you can play these two off eachother to get a nice smooth transition to off-idle. And this usually solves the stumble when putting it into gear as well.
So what about the timing?
Well, with an automatic; who cares! the engine doesn't have to pull at idle, it has a fluid coupling! All you have to worry about is that by stall speed, the timing is back to where it needs to be.
So then if that is true, then after you have the relationship between the transfers and the mixture trimmers dialed in, THEN, you use the timing to set the idle speed. And finally, you introduce idle-bypass air, if your cam calls for it, to clean up the exhaust and or smooth the idle out. But be wary of adding too much air on a rich idle...... cuz the idle-speed will go up, and then you will have to take timing out. Cuz you already established the T-slot to trimmer relationship, and can no longer use the speed screw.
And round and round it goes.
So what is the answer?
Understanding is the answer.
Every engine will have a desire for a unique T-slot exposure to trimmer relationship, and modified by how much idle bypass air it is getting. The initial-timing is only used to set the idle-speed; and yes you can trade timing for bypass air.... and vice-versa, to a small extent.
Then the power-timing is established.
Then the starting and ending points of the timing curve are established.
Then the shape of the curve is established.
Sometimes/usually the above two are done simultaneously, because that's all that the factory type parts will allow, and sometimes it gets to be a crapshoot.
Now you have established, to a large degree, two things namely; 1) the power-timing for all rpms at or near exactly ONE load setting namely WOT, and 2) the idle timing/ tip-in. In other words, the timing is exactly right just two times; at WOT, and at idle; ergo at all other rpm and load settings; the timing is dead wrong.
Now comes the fun part; making the Part-Throttle/ load timing right, using the Vcan; or at least, as close as you can.
So now, where does the tune start? Answer;Establishing the T-slot exposure to trimmer adjustment.
And I always say;
On carbs with transfer slots;
Remove the carb, flip it upside down and set the Transfer-slot exposure to between square and slightly taller than wide. Square with small cams, to taller with bigger cams. Put it back on and reset the trimmers to in the center of their adjustment range. Pull in some timing and crank it up. Then back off the timing to whatever in-gear idle-speed your cam likes; typically 650 (+/-50) in gear for for most street cams with stalls around 2000 or better. Then finish up by fiddling with the trimmers.
On carbs without transfer slots, IDK.I haven't seen one in a very long time.
With a manual trans, that's a whole nuther story.
