Popping sound in exhaust
Gotcha, so it won't idle with less than 40° initial?
If that's a fact:
then I'm pretty sure the valves ain't working right.
The thing is, at idle, the Vcan is not working anyways if on the sparkport. And if on the sparkport,with a properly timed cam and fully functioning valves, it will be at least 1500 to 1700, in Neutral, before any signal at all will appear there. And the signal is usually too weak to operate the Vcan, until a lil later bringing in just one degree at a time, to peak at somewhere after 10" vacuum.
It sounds to me like the throttle is waaaaaaaaaay open, and the idle is still waaaaaaaay low, and that only happens, in conjunction with mega idle-timing, if the cam is running retarded.
Unless maybe you have a pair or two of plugwires crossed; each pair on a different crank revolution. Lots of guys get 5 and 7 crossed,which are on the same crank revolution. So now you have a V6 but at least one of those is firing on an intake stroke sending fire into the intake . Of course this destroys the manifold vacuum, and with that, the engines power; and so you have to crank up the idle speed to keep it running.
Imagine a second pair of consecutively firing cylinders are crossed up. If you have a second pair on the next crank revolution doing the same thing, well now you double the trouble, and have to kick in some advance to keep it running. Now you have a V4, but the engine is fighting those two backfiring cylinders, so it's a really low-powered V4 with way too much timing,way low manifold vacuum, and a waay increased curb-idle screw, and popping in the intake as the fire lights whatever is in there.Of course the unburned gas from the non-firing cylinder is collecting in the exhaust system, and is also popping every time it catches fire.
You can only screw up in pairs. 5 and 7 are common cuz they run next to each other on the engine, and also in the cap. No others do that.
Even just 5 and 7 , when it happens, makes a miserably running engine. Imagine two other successively firing cylinders doing some kind of dance.
I'm just speculating, as to 2 pairs crossed,as opposed to one pair; cuz one pair I know about. Two pairs, I have managed to avoid all my lifetime. A retarded cam I have also experienced... more than once,lol.
Just to be clear; the firing order is ; 1-8-4-3-6-5-7-2, the first 4 on the one revolution, and the second 4 on the next revolution.
Put a vacuum gauge on the intake at idle; it will tell you amazing things.
or, just start pulling off plug wires, one atta time, until the popping stops.This is called isolating the problem cylinder.
