With a stick car, the carb has to be dialed in pretty sweet.
It's not like an automatic, where you can get away with murder. Automatics between idle and stall-rpm can be pretty ugly and guys like it because they can "hear the cam".
You can't get away with that in a stick car, cuz she spends alotta lotta time below 3000 rpm, and has to pull sweetly in that zone.
Proper timing and the 10.5 with a slightly reduced mainjet will get you some of that.
If you put a vacuum gauge on that engine and slowly rev her up, you should find the vacuum increasing until somewhere in the early 2000s and then it will hang at that vacuum for a while. The lowest rpm that it achieves the highest vacuum, is where the engine first becomes efficient with the current camshaft. You want to drive there for best fuel useage not necessarily best mpgs. But that is where your engine will typically become a joy to drive. For a Mopar streeter, this usually drops in between 2000 and 2400. But for your combo IDK.
In any case, because that is the beginning of the sweetspot, yur rightfoot is gonna gravitate towards being there. For my combo, the sweetspot is 2200 to 2800, and then again at or near peak-torque.
The thing is, with a stick car, and a starter gear of around 11/1 and 25.5" tires, 2200rpm is ~15 mph. So whenever your mph is below that, the engine is not where it likes to be. Typically, us mt guys blast thru there because of the engines grumpiness to being there. But it doesn't have to be that way!
The cure is in the tune.
Assuming you have the right size carb, for starters; then at and below 2200rpm, your engine does not care what size MJ is in the carb; you can take it right outta there and it will make no difference.
What it cares about, is the stinking timing, the position of the throttle blades to the transfer slots at idle, and the PV timing, coming off idle. After that, you get on the IABs to fine tune it.
The stinking timing at low-rpm is where just about every m/t self-tuner screws up. He tries to throw timing at it like the automatic guys do. Which if your cylinder pressure is in the basement, you can sortof get away with.
But as your cylinder pressure rises, the engine becomes more efficient, and so more powerful at small throttle openings...... like at below 2200 in first gear lol. With a manual trans, this translates to bucking...... because there is no Torque Convertor to suck the pulses up, and Mustang guys typically have featherweight flywheels, so that is the opposite of what you need to tame the pulses.
But the easiest cure for that, is to light the fire a lil later, so the power pulse are less strong and occur well after the optimum crank position. Below 15 mph/2200rpm,and cruising or lightly accelerating, your combo does not need optimum power, it just needs to behave itself.
Your 13* idle-timing is a step in the right direction. So if you are NOT experiencing bucking at low-rpm, then you are on the right track.
As an example; I run 14* in my 367 which works well most of the while. But not at closed throttle and driving reallt slowly. My idle speed is 700, so with my starter gear and tires 700=5mph. So that would typically be called my slowest roadspeed.... but the bucking starts right there, so I gotta put a lotta toe on the pedal to smooth it out. But at 5* timing, she will idle smoothly down to 550rpm in gear and pull herself around at 4mph without bucking. So now I can parade with the automatic guys. That's probably partly due to the 180psi cylinder pressure, of this 367. So I'm just pointing out what is possible. I am not recommending you try 5* of idle-timing. This 367 has a 230@.050 cam in it, probably close to 3 sizes bigger than what's under your hood, so mine is apt to be waaaay more jumpy than yours.
But here's the deal; to make the engine run on retarded idle-timing, you gotta pull some tricks out of your tool-kit, to fast track the timing back up to normal by around that same 2200. But you still gotta hit the power-timing at 3500. And, the fueling has to keep abreast of that too.
And that is where the rate of advance, and the Vcan, and 10.5PV come in.
But I digress;
Back to post #2,
and pay attention to the other guys that often show up to help. I doubt any of them will accidentally steer you wrong. Your problem should be an easy cure.
One thing I should mention is this; I never begin a tune without knowing the cylinder pressure is at least even across all cylinders. It's amazing to me how many issues can track back to a poor valve seal on even just one cylinder.
At 18/19 inches of as you say steady-vacuum, I'm not pointing to a compression test, but I am questioning the gauge reading for that cam at 750 rpm and 13* of idle timing. If it is the same cam as the 84 TBI GLX's got, working from memory, that cam didn't make anywhere near that. But then, the TBIs didn't idle at 750 either,lol; so IDK. Very interesting none-the-less.
