Timing

[T.Hanson]

I got the timing so advanced it wouldn't take throttle.

Check distributor advance springs work. Start with static setting. Plug both distributor vacuum lines, light on # 1 wire, use nut/screw on throttle body to increase idle to 2100 .

Rotate distributor to center ball on pointer in bell housing window. Which effects the idle R.P.M..

Do we adjust the throttle body screw to return to 2100, rotate the distributor again, over and over ?

In the end I pulled the light, connected the vacuum lines, set the throttle body brass screw to five turns out and rotated the distributor to the place where the engine started promptly and would take throttle stabs, quickly responding. Turns out that's a fairly specific place. Just a dab too far advanced and it stumbles, chokes on the fuel input.

Still wonder why it has a random miss at idle. Rrrr, ftt, rrrrrrr, fft, rrrrrrrr, ft ft.Rrrrrrrrr.

[Karl in KS]

I run my car with a little extra advance by setting the timing at 1700-1800rpm instead of 2200. That gives strong throttle response and pulls all the way to the rev limiter. Like you said, as you add advance the idle speed increases. But a second adjustment--bring the idle speed back down then reset the timing a second time--is all that's needed to finish. You don't have to chase it all day.

And these engines are always lumpy at idle. But if you've really got a miss, check the condition of all the ignition stuff--rotor and cap and wires.

[Brian Smith]

I run my car with a little extra advance by setting the timing at 1700-1800rpm instead of 2200. That gives strong throttle response and pulls all the way to the rev limiter. Like you said, as you add advance the idle speed increases. But a second adjustment--bring the idle speed back down then reset the timing a second time--is all that's needed to finish. You don't have to chase it all day.

And these engines are always lumpy at idle. But if you've really got a miss, check the condition of all the ignition stuff--rotor and cap and wires.

One could remove a little advance at idle by mechanically limiting the vacuum advance pot mechanism a little after setting the timing like Karl's, but once you start looking at the mechanisms for all of that stuff, such as the mechanical advance weights and springs... Well, at least when I look at that stuff, I can hardly believe that cars run at all, and for decades (for better or worse) on the same distributor. It makes me want to go MS like Mr. Florence and gain additional benefits!

Advice (not for the paranoid!) - use a digital dial-back timing light sometime, and watch the combination of the display's tachometer and where the light is finding a mark on the crank pulley. With known good plugs/wires/cap/rotor/fuel pressure, if the timing mark is migrating more than a degree or so and the idle is fluctuating by over 80rpm or more, there is probably an ignition-related cause and effect interplay going on there.

That said, I find it much cheaper to obtain a stable, predicably smooth idle with the dizzy-spinning M30 engines than with a motronic M30. There aren't as many parts to deteriorate and troubleshoot. Take notes about what you change, if in doubt, so you can return to where you started, but there's not a lot to be afraid about experimenting with in there.

[alotawatts]

And these engines are always lumpy at idle.

Thats seems to be the norm but can anyone speak for a dead-smooth idle ? One of mine is......almost.......

[Mike W.]

One could remove a little advance at idle by mechanically limiting the vacuum advance pot mechanism a little

No, I think the vacuum advance only comes into play in transition modes. If you look at where the vacuum port is, it is before the throttle butterfly at idle. So it shouldn't have any affect at idle. And at full throttle, manifold vacuum is at near zero, suggesting again it would play no part. But crack the throttle open some, and it puts the vacuum port just behind the butterfly and under some vacuum.

If you want a smooth idle, with worse gas mileage and more emissions, disconnect the O2 sensor. It's feedback with the ECU always swinging rich/lean is the cause of the hunting idle. Literally, it can't make it's mind up, and pretty much every, if not every early O2 equipped car is that way. It was a great advance in emissions controls, but part of the deal was a less than perfect idle.

[Brian Smith]

If you look at where the vacuum port is, it is before the throttle butterfly at idle. So it shouldn't have any affect at idle.

Mike, you're right.
The port for the vacuum advance does not receive vacuum at idle, so changing the vaccuum advance curve won't affect idle speed. Thanks for the correction. Wrong idea on my part.

-Brian