Here's the clue;
That's helpful as mud in your eye and means exactly nothing.
But that's Ok cuz timing ain't the problem.......
unless you set the timing to "spot on", with the V-can hooked to full-time vacuum, which for a 318 is TDC to 5* advance. Then when the vacuum falls away the Vcan will drop about 10 to 20 degrees and the timing goes to as much as 20 degrees retarded....... but hey, it's "spot on" you said .........
Your problem, if not the above;
is 100% caused by ....... AFR went lean.
And the answer to why that is, is likely one of the following three things, or some combination of them.
1) insufficient transfer slot below the primaries
2) Secondaries opening too fast, or without with fuel in it, see #3
3) lazy or insufficient pumpshot
BTW
When you slam the gas pedal down, it would have to be a mighty big vacuum leak, to make a difference, cuz the vacuum goes to near zero, which not coincidentally is near 1 atmosphere, which is 14.7 PSI.
Typically, small vacuum leaks are only troublesome at very low rpms.
Getting back to setting the timing;
Your engine has at least 4 or 5 target timings that you have to engineer
1) is always, Power-Timing
2) is Stall-Timing
3) is Idle-Timing and
4) between Stall-Timing and Power-Timing is the rate of advance and "all-in-by" timing.
5) is Cruise Timing
Like I said "spot-on" means nothing.
BTW2
if the secondaries are
Not closed up tight but not sticking, that, on a small cam, constitutes a vacuum leak. Your primaries will have to be closed up in compensation. This will cause a very low fuel flow out the Transfer-slot exposure, which you will then have to crank open the mixture screws to get. So Ok, it idles. But as soon as you tip-in the throttles, the transfers are slow to respond, and you get a hesitation. Then once the transfers are flowing, the AFR goes rich...... because the mixture screws are cranked open.
So the lesson is
Set the T-slot exposure to square, and the mixture screws to about 1.5 to 2.5 turns. Then set the idlespeed with ignition timing.
What idlespeed you chose will depend on a few other things, like how big the cam is, standard or auto trans, how tight the convertor is, etc. ; the typical range is 550 to 650 rpm, in gear; and 100 to 150 higher in Neutral
