Getting the timing adjusted.

[Lugnutz65]

This is a fresh 1965 SBC 283 rebuilt by Carolina Machine Engines here in SC.
Rochester 2Jet carb. Cast iron manifold and ram horn cast iron exhaust. Bored 0.060 over. Hypereutectic pistons and a 268H Comp Cams flat tappet cam.
New points style distributor with Pertronix conversion. No points or condenser.

I’ve got the timing set to where it will start cold without any choke. Idles well at 750 RPMS and drives fine without stumbles. Engine is too fresh to do any hard pulls or hard accelerations. Medium acceleration is great though.

I did all this testing because the timing seems to have a lot of advance.

Here are some numbers for us to ponder.

I’m very methodical but have only one set of hands. I’m lucky to have a retired neighbor who enjoys helping me in the shop. I’m using an INNOVA timing light with flash delay and digital tach.

I brought the engine up to temperature and tested 4 things . . .
MECHANICAL ADVANCE with the vacuum line plugged.
MANIFOLD VACUUM from a large port behind the carburetor (see photo)
CARBURETOR vacuum line.
TOTAL ADVANCE with the carb vac line connected to the dizzy.

Like them or not, here are the numbers I got. If anything seemed unusual, I went back and tested again. I think I would get the same numbers if I did this again tomorrow.


MECHANICAL ADVANCE with the vacuum line plugged.
570 RPMs = 12°
750 RPMs = 12°
1000 RPMs = 15°
1300 RPMs = 23°
1500 RPMs = 24°
2000 RPMs = 27°
2500 RPMs = 32°
3000 RPMs = 35°
3500 RPMs = 40°


MANIFOLD VACUUM from a large port behind the carburetor
750 RPMs = 32 cm Hg (13 inches Hg)
1000 RPMs = 40 (16)
1300 RPMs = 47 (18.5)
1500 RPMs = 50 (19.5)
2000 RPMs = 54 (21)
2500 RPMs = 54 (21)
3000 RPMs = 54 (21)
3500 RPMs = 54 (21)

CARBURETOR vacuum line
750 RPMs = 20 cm Hg (8 inches Hg)
1000 RPMs = 24 (9.5)
1300 RPMs = 35 (13.5)
1500 RPMs = 40 (15.5)
2000 RPMs = 47 (18.5)
2500 RPMs = 50 (20)
3000 RPMs = 50 (20)

Timing results WITH the carburetor vacuum line CONNECTED to the distributor.
750 RPMs = 25°
1000 RPMs = 27°
1300 RPMs = 36°
1500 RPMs = 38°
2000 RPMs = 44°
2500 RPMs = 46°

[Accelo]

Is the little stop for the weights gone? Seems the are missing or broken on most old distributors. While you are in there be sure the oil wick is still also there. It keeps your points from wearing prematurely. Most builders like to keep the distributor end play to about .020.
This will also keep your timing from bouncing back and forth.
Cheers

[Lugnutz65]

It has a new points style distributor with Pertronix conversion. No points or condenser.

[Accelo]

I should read more methodical!
Still your timing should typically 34 deg or so.
I agree you have to much timing. You didn't say if it pinged or not?
Possibly because no full throttle runs?
Do you know the compression ratio?
Very clean engine bay. Looks great.

[Lugnutz65]

Originally Posted by Accelo

I should read more methodical!

You read correctly! I went back and added the info to the original post. LOL!

Engine was properly broken in on a run stand but has not had any hard pulls or hard acceleration yet. Still treating it gentle for the first 1000 miles. No pinging at all. Drives great.

[Accelo]

Every motor is different. I would get some miles on it.
Take it and start on a hill and do some full throttle runs.
If it pings run some higher octane fuel and try it again.
If it runs good and doesn't ping go by the function.
That's the bottom line.
Love the old motors. I had a 283 that was a .090 overbore.
Some have ran them as much as .125 over. (A 301CI motor)
Unlike my current LS1, it has a max overbore of .005.
BTW, I have been reading your T5 information on the Web. Well done.
Cheers

[Ziegelsteinfaust]

You have something wrong with your distributor, someone really modified it. or you weights are too loose. You don't usually need more then 36* total, and I like 15* initial myself.

You have 28* of movement where the vast majority of distributors have 21 maybe 23* of movement.

My LT1 with 10.7-1 cr, Comp 306 cam, afr 195e heads circa 1994, Demon 750 mechanical secondary, and Pertronix distributor idles at 750 rpm in gear. With 14* initial timing. Starts up as good as most carbuerated engines.

[AussieinNC]

I suspect the distributor has been modified for use without the vacuum advance mechanism. I would just plug that vacuum line going to the distributor and run it as a mechanical advance unit.

Set initial timing to 13-14 degrees and let the distributor do its work....

Very nice install and those vacuum figures are excellent! Great work....

[Lugnutz65]

The distributor is brand new. Never modified. I bought it from Rockauto.
I expect some of you will give me negative feedback for buying a distributor from Rockauto.

I reduced the initial timing from 12° to 9° of advance. The timing with the vacuum line connected also dropped 3° as expected.
At operating temperature it starts right up and idles fine at 750 RPMs after doing a little idle screw and throttle adjustment. I will see how easily it starts cold tomorrow. I don’t mind if it needs a little choke.

I took it out for a drive and it runs just fine. No stumble. No pinging. It seems to need a little more throttle to get going smoothly from a standstill, but that may be the only change I’ve noticed. I pulled a hill that was half mile long in fifth gear with no pinging. I was lugging the engine on purpose. If I should pull the hill at higher RPMs instead, just let me know.

[Lugnutz65]

Someone suggested the weights are the cause of the problem. I found this pic I took when I first bought the dizzy. I have since converted it to Pertronix but the weights are the same now. The weights look similar to other points distributors I see in Google Pics.

[Accelo]

The factory timing stop goes on this pin. As viewed from the bottom side of the distributor. The bushing is missing in the picture.
I have included some timing specification from GM tech department.