DansYellow66

If I'm following your post correctly, you might want to experiment with wrapping your weights with rubber bands to hold them retracted and check your initial timing. For terminology I refer to your distributor setting as initial or static timing; centrifugal advance as mechanical timing; and both static and mechanical timing as total timing (minus vacuum). I suspect you are getting some centrifugal (mechanical) advance while at idle which is masking your true initial static timing and amount of centrifugal advance. My BB is subject to this in order to use light enough springs to get all my mechanical advance in by about 3000 rpm.

Some guys think this is perfectly OK to have some centrifugal advance in at idle and with a stock engine with a mild cam it probably does no harm. However, if you have a pretty lumpy cam and the low end is a bit weak - if you are like me you take off in first in a normal manner by giving it a little gas (which brings in more centrifugal advance) and then release the clutch fairly quickly to avoid excessive slipping which usually drags the engine speed back down - even below idle a little - and all that advance drops back out, engine loses power as a result and you end up stumbling away as the engine tries to recover. It doesn't make for the best street manners.

Ideally I would like to delay my centrifugal advance from beginning until at least slightly above idle. But setting up distributors is sometimes about compromises.

Every engine will be a little different but even with a 12 deg vacuum can I was getting too much advance at cruise with 36 degrees static and mechanical and it was constantly missing/surging. I had to make a limiter for my vacuum can finally to get it down to 8 degrees vacuum advance to solve this.

tbarb

I think the B-26 vacuum control gives 15* @ 12" vacuum so it sounds matched to your engine if you use full manifold vacuum advance.

How far out are your idle mix screws adjusted. I believe the reason the engine smooths when you retard the initial timing is because you give the diluted idle mixture longer to compress which makes more heat and the mixture lights easier. The idle smell you think is rich could be incomplete combustion because of the above. If you get the timing close you can lean the idle mixture by reducing the idle feed restriction by .002-.003 and see how the car runs.

A good indicator if the idle jet size is close is with the transfer slots set almost closed (little squares) the emulsion screws are approx 1 to 2 turns out at warm idle.

The way your distributor is set up it sounds like you could use ported vacuum advance, set the initial timing at 18*+- and then experiment with different vacuum advance controls using a ported source. If you decide the use full manifold vacuum advance I would think 10-12* initial timing would be good but that may cause the total centrifugal to fall short.

63 340HP

John, review what you wrote and adjust to match the reported benefit.

35d total at 3000 rpm, no vac, is good.

The resulting 17d at idle, not good.

12d at idle, better.

The solution is more centrifugal advance, from the reported 18 degrees (35-17), to a less aggressive 23 degrees (35-12).

You may need a skinner advance stop pin collar, or just a squeeze to pinch more slot travel from the existing collar.

​​​​​​​Use what you find to work best at full rpm, and at idle, to guide your direction in adjustments.

​​​​​​​Get the full rpm and static idle rpm timing optimized, centrifugal advance first, before tuning vacuum advance.

SWCDuke

The 365/375 HP engine spark advance map works as well with the LT-1 or Duntov cams as it does with the 30-30 cam... actually better because the two former cams make more low end torque.

It's that simple!

Duke

TCracingCA

Also don't forget to factor in the camshaft if not installed straight up!

cardo0

Don't be afraid of dynamometers and O2 sensors. That's the modern way to tune and what every professional racing team uses. Not cheap but most dyno have a wideband O2 for tuning customer cars. Many times a dyno shop will run specials or have club discounts.

Good luck.

63 340HP

People fail to recognize the 24 degrees of advance travel in the correct SHP spark advance map is aggressive enough for most high performance cams. Get the travel correct and then tune with springs.

mrg

The pistons are hyperutectics, yes. Compression ratio comes in at 9.75 with a .015 steel shim head gasket. Backing off the static timing to 12* looks to be a good starting point. Anything lower, the engine labors and wants to stall unless idle screw is turned up significantly. I haven't tried holding the advance weights in place with rubber bands. The timing is stable at 950 rpm. No notable balancer timing mark jumping around to suggest the advance weights coming in early.
The B26 vac can replaced a B28 that was in use. The B28 seemed to add too much ignition advance at too low an rpm to induce a trailer hitching condition. The B26 vac can worked out better.

​Also in the works is to refresh the distributor with a rebuild kit ordered up from Willcox. The rebuild kit includes a new shaft, drive en gear and housing, and button.

​​​​​,https://willcoxcorvette.com/media/catalog/product/cache/1/image/940x587/f64e6f78ad8ff0f538d56bcc7762581b/d/i/dist001-corvette-part.jpg

The idea is to add a plunger stop while the distributor is apart.
All suggestions appreciated. .. Thanks, guys.
John

BTW, wanted a to add:
While monkeying around with the timing light trying to get it just so, the positive lead clamp on the timing light rotated slightly and shorted out against the left side vertical spark plug wire shield. The engine sputtered, then died. The 30 amp fuse that was added to the large black wire that connects at the center solenoid post blew. Smoking wires aside, this is the second time the fuse has blown. First time was a Pertronix install that went slightly awry. ..