That doesn't change what has been said thus far.
That engine in stock trim, should be able to tic over at 450 rpm in gear/ 500in Neutral.
"extra idle-timing" with a stock engine, will lead to extra idle horsepower, which shows up as an increase in idle speed. In compensation, you will most likely crank the idle speed-screw out.
Most likely, this action will upset the transfer slot to mixture-screw relationship, and three things will show up, the severity of which being in direct relationship to the severity of the mismatch.
1) you will get; a tip-in sag, or a hesitation, or a flat-out bog, and
2) your low-speed fuel delivery, OFF-idle will go rich, leading to soot-fouled plugs..
3) your fuel-economy will plummet
4) you get the dreaded idle-speed disparity from neutral to in-gear. Ok that's number 4, lol.
Do yourself a favor; set the transfer slot exposure FIRST to prevent those ugly manifestations, then use ignition timing to set the idle-speed. This will; kill the Idle-power, which will kill the banging going into gear, while simultaneously narrowing the disparity between Neutral and in-gear idle speeds, and allow you to lean out the mixture screws which will kill the plug-fouling, and improve fuel-economy.
If the stock-engine will not tic over at or near 500rpm in gear, visit the cooling system temperature and then the valve lash. (see below)
AFTER the idle-timing has been settled, revisit the power-timing and AFTER that, tune the Vacuum-Advance system.
Finally, for training purposes, AFTER everything including the Idle-timing has been settled, try this; without regard to reading the actual timing numbers;
advance the timing bit by bit, until either you run out of adjustment OR until any further addition of timing produces no increase of idle speed. When you find that rpm, you have found the max timing for the existing conditions. Now, read the timing. Don't be surprised to see a number deep into the 20s even early 30s.
Obviously you cannot run the engine in this state.
Put the timing back.
The point of this exercise is this;
Say you get 32*,
but to satisfy the Transfer-port synchronization to the mixture screws, the engine wanted say 5*, which is about as far away from 32 as can be imagined. Your engine is idling at say 27* retarded...... and is happy about it.
Now take a moment to ponder this. The only idle-timing that you can run, within a very narrow window, is that which avoids the above mentioned 4 situations.
Ignore what others may advise what your idle-timing "should" be.
Ignore what I say; you won't hurt my feelings, lol.
Ignore-NOT what the engine tells you about avoiding the Four dreaded idle/off idle situations. It's "only the idle", make the engine happy, because every time you take off from a stop, a crappy idle tune will tell you all about it.
BTW
do not confuse a tight valve-lash with making power. Looser is usually better.
The more retarded the idle timing is, (and as we have seen, your engine may be idling around 27* retarded before you get it figured out), the more heat will be going into the cylinder walls and, the more heat will be going thru the exhaust ports and into the manifold. This means, the exhaust valve is gonna run hotter than it needs to. That's just the way it is.
The valves, especially the exhaust, have to spend time on the seat to give up the heat of combustion. With a too tight lash, this may be not enough time. If your engine starts to idle rough, it may be due to a too-tight lash.
IIRC the factory lash settings are .010int./.020exh. Do not be afraid to open them up 10>20%, then backtrack later on.
I have always run my slantys at 195*F, and ALL of them liked at least .013int/.023exh., and I set them at ambient temp, say 75>85*F, cuz who the heck can get to the valves fast enough to set them any where near to operating temp, and I'm not fan of setting slantys while running
because;
If you ever inspect your rocker arms, you will almost invariably find that the valve stems have worn a rut into them, which requires a narrowed feeler to ride in there. Yeah; just try keeping your narrowed feeler in the rut with the engine idling and simultaneously adjusting the dancing nuts. I got a lotta patience but not enough to suffer this. So, now you know, almost everything that I know about tuning a slanty.
Oh yeah, almost forgot;
before you do anything, check the float level. The engine, at idle, is fairly sensitive to having a specific and steady WET fuel level.
If it is too low, pull-over gets difficult, relying heavily on the vacuum signal.
If it is too high, pull-over will be too easy, resulting in a rich idle. This can be corrected by adjusting the mixture screw lean, and it idles just fine. But now, just try to drive away without a lean tip-in stumble.......
Happy HotRodding
