I have a 63 but it has a later engine. I'll give the specs and then get to my question.

The block is a 4 bolt 250 hp 350 made in 1970. It was used in light trucks and Camaros. Intake is a 1965 Corvette 250 hp, distributor is 1973 250 hp. I'm running an Edelbrock 1406 600 cfm carb in it. The heads are 350's, I have roller rockers in the engine. I don't know what the compression is but when I rebuilt the car I chose low compression heads to run pump gas. I think I remember putting a very slightly spicey cam in the engine. I have an M&H Electrics 1 wire electronic ignition conversion in place of points.

All the info I can find for that engine combo with a manual trans, which mine is, timing should be TDC. For auto trans its 4 BTDC. I set it at 4 degrees without vacuum advance, 725 rpms.

More information I have is that the advance timing should be about 32-34 degrees at about 2500 rpms. However, mine is showing 41 degrees. Am I in a danger area? Before I really studied the parts I have I've run the engine at 10 degrees BTDC initial timing for several years and it seemed to run fine. No pinging, etc. But the more I read the more I see that 10 degrees may be way too advanced. Any thoughts?

I realize there is latitude for performance in the factory specs. so I'm not a stickler for factory info. Its not a race or performance car; mainly a daily driver type but I would like to get the best performance and gas mileage in what I have to work with.

 

Set up your total timing to 36 degrees and assure that it's pegged out at 2800-3000 rpm. Once done, verify that your initial is in the low to mid-teens. If it's not, correct the length of your centrifugal curve by using an advance stop bushing in combination with custom-tailoring the length of the advance slot. Make sure your vacuum advance meets the "2-inch rule" and that it is limited to an additional 12 degrees. Hook it up to manifold vacuum, which should give you actual timing at idle of about 25-30 degrees. Maximum total combined timing with full centrifugal and vacuum advance hooked up should be 48 (36 total plus 12 vacuum). Done.
Lars

 

Thanks, Lars, but I must admit that some of that went right over my head. My vacuum advance is a B9 and is plugged into the driver side vacuum port on the bottom front of the carb.

So I keep the vacuum advance hooked up, rev the engine to 2800-3000 rpms and adjust the distributor to get to 36 degrees?

"correct the length of your centrifugal curve by using an advance stop bushing in combination with custom-tailoring the length of the advance slot" I have never heard of this.

"actual timing at idle of about 25-30 degrees"- that is with the vacuum advance connected?

 

I just checked the idle timing with vacuum advance connected, 700 rpm. The timing light shows 23 degrees.

I just noticed from some 2021 notes that I installed # 26 Autolite spark plugs and for some reason gapped them at .045" instead of .035"
Would that cause any ill effects?

I forgot to add that I have no idea what weights or springs are in the distributor.

 

Plug gap won't hurt anythng, but you're inviting misfire at elevated rpm and cylinder pressure. Just re-gap to .035".

23 initial without vacuum advance is too much. What's your total timing, pegged out, without vacuum advance? Set it to 36 and see where initial ends up. You don't need new weights - the stock weights are the best you can use. You also probably don't need different springs unless the stock springs have been removed. Note the rpm that pegs out your centrifugal and set timing to 36 at that rpm. If that rpm is anywhere between 2500 and 3500, don't worry about changing springs - it's close enough for all practical purposes.

 

No. Total timing is never set with vacuum advance hooked up. Yank the hose off (doesn't matter if you plug it or not) and set total to 36 when the timing pegs out at elevated rpm. Note the rpm at which the timing no longer advances with more rpm - that is your total timing rpm.

Yes, as I noted above: "Make sure your vacuum advance meets the "2-inch rule" and that it is limited to an additional 12 degrees. Hook it up to manifold vacuum, which should give you actual timing at idle of about 25-30 degrees." Your "B9" vacuum advance is producing WAY too much vacuum timing, so you need to limit it with a vacuum advance limiter. That B9 will give you over 20 degrees of vacuum advance. You need to limit it to 12.

The driver's side lower vacuum nipple is manifold vacuum, so that's correct to use.

All of this is covered in detail in my papers. E-Mail me for a copy.

Lars
V8FastCars@msn.com

 

I'm a little clearer now. I thought I'd read that total timing was set with the vacuum advance connected. If my initial timing is set at 4 degrees without vacuum advance, 41 Degrees at 2500 rpm is probably because vacuum advance was connected.

My 23 degree idle timing was with vacuum advance connected. Its 4 degrees disconnected.

On my Edelbrock carb I can feel constant vacuum from the port the vacuum advance is connected to.

"Your "B9" vacuum advance is producing WAY too much vacuum timing, so you need to limit it with a vacuum advance limiter. That B9 will give you over 20 degrees of vacuum advance. You need to limit it to 12."

Would it be better to just use a different vacuum advance? A B1? NEVER MIND, I just saw a 2015 posting by you regarding the limiter and that proper vacuum advances are not available.