total timing reading accurate with no load?
Thank you I did read into that, and I figured since idle was a light load as well it may as well get the vacuum advance by hooking to manifold vacuum.
Ah. So many of us did 'cause it seems that way. The explanation seems to be that at very low rpm the engine's power is very low too. So as a percentage of what the engine can make at idle speed, its a moderate load. maybe the engine make 30 hp and loses 5 - 10 to internal losses. Slipping it into gear, especially with an automatic might take another 10hp.
What I can't seem to figure out is if the initial timing is bumped almost 10 degrees over stock, should I bump the stock idle speed as well? For my truck the recommended idle was 750rpm. After I recurved the distributer and adjusted the timing to 16 intitial, it bumped my idle up to 850. I'm wondering if I should just leave it at 850 or do some more adjusting and set it back at 750
Can't think of any reason why it would be good to idle higher.
If it idles nice at 750 then I would go back to that. *
Without any other info. the practical test with an automatic to tune in will be to set it for most power at idle in gear.
When shift into drive, the rpm shouldn't drop, or drop very little.
Another check is the manifold vacuum in drive, at that rpm is an indicator of how strong it is with the load.
So an example of this first round of testing.
850 rpm, 16* in N
reduce idle speed via throttle stop screw.
750 rpm, 16* in N
shift into D
650 rpm, 16* in D
Compare with previous settings. Lets pretend it was
750 rpm, 14* in N
shift into D
700 rpm, 14* in D
Therefore in the above example, 14* initial is the stronger one. Go with that.
*There is another effect when changing the throttle position at idle.
That's why I put an asterisk up. The throttle can only be changed within a small range before the effecting both the idle mixture and the off idle mixture.
This is particulaly true with Holley 4150/60 type carbs.
So...the practical next test is to try some very gently accelerations from stop, along with some more moderate accelerations from stop. If there is a lag or delay in response, then the initial throttle position is out of range.
Adjusting the idle mix screws can help make up for loss of fuel at dead idle (probably need to open them more when reducing throttle position)
They will only have limited impact in helping the off-idle.
Keep track of how much you turn each of these three screws (idle stop, and idle mixture screw).