Too many changes at once.
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But sometimes you just have to try things, so its all good as long as you learn something.
Eventually you'll get a sense of when big jumps are OK and when they are not. You can generally do that with field artillery and naval guns but not always with engines. Once outside of a working range fluid dynamics of the fuel and air start doing unpredictable things.
Going back to the baseline as you are is the logical move in my book too.
Then make one move from there. I'd say the .035" t-slot is a good one. And since you've done that, try 18 and or 20* and see if you can get it to idle at same rpm and vacuum without opening the t-slots.
Come back to that decision after reviewing some of what has been learned.
That's interesting! While its possible that timing may related to the stumble, removing vacuum advance from the equation did not completely resolve it.
View attachment 1715543422 That's definately something to think on. I've used the Direct Connection Race distributor, which is super fast advance (no vacuum advance) and no stumbles.
I used to think something similar. Its not nuts, but its not correct. Or maybe it is nuts, but then I'd be admitting I'm crazy too.
First of all, timing's relationship with mixture density (which is more or less the same as how rich the mixture is in the combustion chamber) is tied together. In a lean running or other slow burning condition, more time is needed for the burn to build maximum pressure as the piston is going down.
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Second, with a high overlap cam the idle vacuum is already somewhat low. If you recall the 'idle circuit' uses the manifold vacuum to move fuel from the bowl to the idle and transfer ports. So when the
both air flow and fuel flow was reduced. Opening the throttles brought in more air, but not a proportional amount of fuel.
Take the carb off, measure t-slot openings for 1/4 turn increments of the adjustment screw. Start from just touches to .045 or .050 open.
If your chicken scratch is getting impossible to reference, copy it over neatly into a spreadsheet or a fresh sheet of paper or whatever works for you.
My carb notes (almost) always goes onto a spread sheet later that day or week. I also print some stuff and copy things onto 8.5 by 11. Most now goes into file folders which I can grab easily. A few things still go into 3 ring notebook - which was my initial method or organizing.
Returning to the next steps:
Going back to the baseline as you are is the logical move in my book too.
Then make one move from there. I'd say the .035" t-slot is a good one. And since you've done that, try 18 and or 20* and see if you can get it to idle at same rpm and vacuum without opening the t-slots.
I don't know what will happen when you try a little less initial with .035
. My guess is that there will not be enough air flow. That's probably why the car was running with .045" of the slots showing. Opening up the throttles let more air in.
So I would plan on it not idling as strongly with only 18 or 20* initial and .035 to .040 t-slots. In which case let more air in at idle.
One method would be to crack the secondary throttles just a little further open. Measure the throttle to base distance before you do this. Or if you have a wire gage you could measure clearance to the wall. There is no other reference for the factory setting! Then give the screw a 1/4 turn. Give it try.
A more easily adjustible method is to put a T in the PCV line. Plug the base of the t and drill an 1/8" hole in the plug. If that helps try 3/16.
(Later you can drill the throttle plates or crack the secondaries.)
See if that brings the idle speed up. It should.
Next, see what the idle mix screws are doing. They should still have an effect on the mix, especially with the t-slots further closed.
But the mixture may need more enrichment. If so, experiment with wires in the primary idle air bleeds.
Once an idle is established that is at least as strong as the baseline (800 rpm 10.5 "Hg). Then try driving it.
If the dead spot is still be there, increase the wires in the IFR.
Cheat sheet for a few IAB sizes.
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So if the 4777 has .076 IABs, and .025" wire is placed in each one, they will be equivallent of .072 IABs.
Run the wire under the aircleaner gasket to secure it. I usually use one wire for both bleeds even though it takes longer to bend up jsut because its easier to keep track of. Two individual wires works just as well.
Typical IABs will be in the .072 to .076 range.
With the air bleeds, a jump of .002 or .004" should noticibly effect the idle through transition fuel.