Distributor tuning

[Yadkin]

Dave, you know as well as I that a Ford relies on a different Periodic Table than a Chevy does.

Back to reality for a minute, what you state makes sense. Referring to my curves in Post 1, I should adjust my vacuum advance to obtain 7 degrees advance at 15 in Hg, connect it to manifold vacuum (under the throttle plates) then set total timing at idle to 10 degrees BTDC (7 vacuum plus 3 mechanical).

That way punching the throttle at idle will set the timing to 3 degrees BTDC (0 vacuum and 3 mechanical), and as the engine speeds up both the vacuum and mechanical advances will increase, so at cruising condition, 2000 RPM, advance will be about 26 to 28 (5 to 7 vacuum plus 21 mechanical).

[scumdog]

I'm not taking sides here but you need to consider air-to-fuel mixtures. I grew up with GM cars that use manifold vacuum. Yes, I know this is a Ford but hear this out:

For initial timing, GM pulls the distributor hose off and plugs it. Then they time at ~6 degrees BTDC. What does this do... When your engine is stopped there is no vacuum so timing is at 6 degrees. As soon as it starts, vacuum advance.

If you punch it at a light vacuum immediately drops off and so does the advance. As rpms increase the distributor weights advance timing even at WOT (wide open throttle). Ease off the pedal and the vacuum adds more advance, as it should.

Punch it again at high speed and vacuum immediately drops off and so does vacuum advance, as it should. Mechanical weights still control HS advance. Lifting the pedal again advances more with vacuum. There is no lag.

Remember, when vacuum is high, air is choked off. In affect, this makes your engine displacement smaller because the air is thin and fuel is reduced. This is where the air/fuel mixture tries to maintain 14.7:1 for the best economy. When vacuum is low, air is more dense and the mixture is rich. This is the time to back off on spark advance. - Dave

What Dave said,
I tried to explain the same thing but it seems that Dave has a better way of saying it!

[Yadkin]

...adjust my vacuum advance to obtain 7 degrees advance at 15 in Hg, connect it to manifold vacuum (under the throttle plates) then set total timing at idle to 10 degrees BTDC (7 vacuum plus 3 mechanical).

I did exactly this and ran it around town than up and back I-40 one exit. I don't like the way it runs as much as before. There seems to be a bog when I mash the gas. Oddly, it also blows oil out the back while accelerating.

Remember I have EFI on this engine. At idle the air fuel target ratio is set to 13.6, WOT 12.5, cruise 14.1. Maybe it's getting too much gas during the transition??

[Yadkin]

I'm working with two guys over at the FAST forum on his. One indicates that I should be running 16 degrees initial timing (the engine idles great at this setting) and a total advance of only 18, for a total of 34 at 3500 rpm. Mine totals at 24, and the curve is too steep. Here's the curve I have now:

[Yadkin]

I can handle the curve issue easily by bending the spring mount tab on the smaller spring. I don't see an easy way to restrict the range though, without fabricating a part.

[Yadkin]

I bought a new Pertronix distributor so I can adjusts the advance curves for modern fuels. It has three different spring pairs, three different limiter pairs, and the pairs can be mixed can be combined. I'll use one silver and one bronze spring (S+B on the chart), and combine limited to achieve 18 degrees total.

[Yadkin]

Why would Pertonix use a larger shaft diameter that the drive gear rides on? I can't reuse my old one. Oh yeah, so you have to buy their bronze gear, spend another $60, and wait another few days for shipping.

At least I have Amazon Prime.

[Yadkin]

I put the new bronze gear in and installed the distributor. I must be livin' right, because I didn't have to bump the engine to get the oil pump shaft to engage. It just dropped in.

I had a little clearance issue, which I sort of anticipated. The Pertronix is about an inch taller than the Autolite, so it contacted the underside of the air cleaner. My solution: "dish" the lower flange, effectively making the cleaner taller, "ding" the area right on top of the distributor, and lengthen the center attachment screw a bit. I have enough clearance to rotate the cleaner back and forth and the spark plug leads don't move.

And yes, the hood still closes.

[Yadkin]

I started it up last night after some no-go cranking. The problem turned out to be the connector that I re-used to plug the distributor into my harness. It was one of those crimp or solder deals, then push into a holder where they snap in and don't back out. The problem is that the gauge of the metal used is so thin that they are easily deformed to the point where no electrical contact is being made. The pre-wired connectors are better, so I have some on order.

Once I got that replaced she started right up. I set the initial timing to 16 BTDC and the idle is nice and smooth. I hear a pleasant "whir" noise when the engine is running that I haven't heard before. Unfortunately, since I'm waiting for parts on my steering rebuild, I can't drive her and test the engine under load.

Working the throttle with vacuum disconnected, the advance retards while accelerating then advances at the higher RPM. Apparently the electronics does this?

I ran the engine through two cooling cycles and shut her down. No carbon deposits on the floor under the exhausts. Another good sign.

[Yadkin]

I finally had time (and good weather) to test drive the car. Huge improvement. There is no knocking at any engine speed or load. My misfire is gone. No more black smoke and rich running condition at idle. I just drove about 50 miles, once up to 88 then later up to 94 mph, and the gas gauge barely moved. At 50 on a two lane the cabin is actually quiet.

That advance issue turned out to be my new timing light. Innova 5568. It allows you to delay the strobe in 1 degree increments. Set on 16 it can't figure out the changes in RPM fast enough to give an accurate flash. Set on 0 the strobe shows the advance operating correctly.

[simplyconnected]

Glad you finally enjoyed success, Steve. I hope this is the last of your problems and you can enjoy the summer cruising in your classic. - Dave

[Yadkin]

No kidding, and thanks. This one was a real bugger to diagnose. I had my old distributor checked out by a guy with a very good reputation, and the engine ran fine before my rebuild. I felt that it was an ignition problem, and replaced basically everything, least expensive on up, and nothing solved the problem.