Optimal Timing SBC 350

[kna4977]

Decal says 8 but that was with 1972 fuel. What is optimal initial timing with todays fuel?

[geezer#99]

I run mine at 14 here at sea level.

[kna4977]

Originally Posted by geezer#99

I run mine at 14 here at sea level.

I’m in the Dallas TX area. Was thinking maybe 10-12 range?

[geezer#99]

Start at 12 and bump it up a couple degrees until it pings or is hard to crank.

[Willshook]

Initial timing is just one aspect of timing - mechanical and vacuum advance are key for performance, fuel economy and drivability.

For mechanical advance you want ~36 degrees at 3K RPM. If the initial timing then ends up over 14 degrees...then you should do some digging to make sure the timing marks are right. Kits are cheap from MSD and Mr. Gasket for weights and springs.

Vacuum advance is a little more tweaky, but unless you have (or want to install) an adjustable can you can ignore it for a daily driver. Just make sure you're using manifold and not "ported" (above the carb butterflies) vacuum.

If you don't want to monkey with this, 10-12 degrees initial is usually in the ballpark. I wouldn't run anything more than that on a daily driver. There's no advantage to "more" timing...

Lots of great articles on this around, but the basic numbers are very well proven on the road, track, and dyno...

[Dead Parrot]

A lot of the early 70's timing numbers were intentionally less then optimal for emissions reasons. If the vehicle had the AIR system, they wanted some unburned fuel in the exhaust so it would burn off when the fresh air was injected in the manifold. Better for clean exhaust, not so much for power and fuel economy. Also, the more advanced the timing, the more NOx that gets made.

If you don't have to worry about emission checks or your location doesn't check timing, then for a stock or mostly stock 350, around 12~14 usually works. Don't worry about exact numbers. Keep in mind you are reading off a mass produced timing mark on a press fit damper using a stamped timing mark tab spot welded to a stamped timing cover. There is a bit of slop in the system.

Do what Geezer said and sneak up on it over a couple of weeks. Unless you want to seasonally adjust things, best to do during a 100*F hot streak. If it starts easy when hot on a 100* day, you should be good for any weather.

For OP, I would adjust to 10 and see how it reacts. Then go from there. It will probably cause a higher idle so you may have to readjust that. While you are adjusting, make sure your vacuum pot is still working. They often quit and not get noticed as the main effect is lower part throttle cruise economy. If your vacuum pot is currently on ported(often the factory option), switching to manifold will also cause a increase in idle speed so another adjustment needed.

[kna4977]

Initial timing appears to be at 12.

I have been working on the choke and getting it set right. Currently closes for cold start right, but once it cranks, it soon seems to run out of fuel and dies.

I currently have the choke pull off opening the flap by about 1/8" Should I adjust it to close further and enrich the mixture?

I reconnected the thermac air cleaner system by hooking back up the vacuum hoses. It works like it should.

I cranked it, and it sounded great out of the left/drivers side, but sounded like it was backfiring, misfiring or just not running right on the passenger side.

I've done no adjusting or tuning on the carb at all up to this point, but found it odd for this to start all of the sudden without any adjustments other than hooking back up the thermac system.

I checked the fuel mixture screws and they were both about 1.5 turns out from closed.

I currently have them out 2.5 turns and it sounds better but not exactly where I would like. Especially on the right side.

Any ideas? What should I look at to get this dialed in?

[Willshook]

What carb?

Double-check the firing order and make sure you don't have something swapped. If you don't, use a timing light to verify all of the cylinders are firing.

[kna4977]

Originally Posted by Willshook

What carb?

Double-check the firing order and make sure you don't have something swapped. If you don't, use a timing light to verify all of the cylinders are firing.

Everything is stock quadrajet. Here’s a sound bite.

https://photos.app.goo.gl/QoU1wp1UB7pPCnmd8

[Willshook]

I'm not sure what I'm supposed to be hearing on that clip; sounds fine to me.

Single best Q-jet tuning guide on the planet in theses threads; lots of background but gets to the meat further down.

https://www.digitalcorvettes.com/thr...by-lars.88376/

[GSP7]

I dont here anything wrong in the Sound bite either

Small air leak in your pipes somewhere???? , or not ??