The vacuum and timing threads are interesting.

My jyd 350 has about 12-14 in of vacuum, with steady fast fluctuations at idle, and the idle mixture screws on the Edelbrock carb are not real responsive.

I tried to set the base timing, with the vac disconnected, at 10 deg. and it would hardly idle in gear.

I see several people here setting base timing ( I think) at 16 to 18 deg. That sounds like way too much, and should cause hard starting, from my experience.

Anyway, I ended up setting the timing on mine at 15 or so, with the vac advance hooked up to ported (venturi) vacuum, and it now idles in drive, although poorly. I am headed to a cam change downward soon.

My thought would have been no more than 10 deg base, 12-20 in mechanical, and the rest in vacuum. Total of 36 or so.

Do you all really run 16-18 deg base timing? And if so, why, and does it start and work ok? This is my first 350 Chevy, so I am trying to learn.

I've run 16 initial (900 rpm or so in park) on mine forever and it starts and works fine. I think a lot of it depends on what you have in your motor now. A "standard" mild sbc will work well at 16 with 20 mechanical. If your starter is decent and you have adequate battery cables, it should be no problem.

When you set initial with the vac hooked up you get an artificially high initial reading and when you put it in gear the vacuum is probably dropping as the rpm drops which causes the timing to retard from initial and the vicious cycle starts.

Try disconnecting the vacuum, setting it at 16 and plotting the timing curve until it stops advancing to make sure how much mechanical your distributor has. (Smog year distributors have a ton of mechanical built in and will be sluggish on a perf motor) I'd run it without the vacuum for a while to make sure it runs ok and as expected. Once that is established you can jack with the vacuum can.

What you need and can run in initial ignition timing depends HIGHLY on what kind of cam you have in the engine.

I have an HR296 with 236/242 @.050 on a 396 with 11.5:1 compression. I run 16-18* initial and have no problem cranking it over with a basic starter. Now with less cam I might have cranking issues, but with less cam I would need less initial as well.

Now to really raise your education level, I idle at 28-30* advance. I do that by having a vacuum advance that is all in at 9" providing a limited 12* advance and connecting it to manifold vacuum. I idle at 11-12" of vacuum.

I have 20* mechanical advance or 36* of total advance. This is a very consistent total advance setting for most Chevy V8 engines no matter what.

So I can advance up to 52* during cruise conditions. Again a very consistent setting for Chevy V8 engines.

I used to have a screwed up vacuum setup and my combination really did not like idling with only 16-18* advance. Vacuum in that messed up setup was only 7-8". I know there are reasons why people recommend running with disconnected vacuum advance to sort things out... but there are also very good reasons to hook it up and make it work right too. For getting the vacuum advance dialed in there is nothing better than a hand vacuum pump so you can figure out exactly what you have in there.

My 350 has exhaust, intake, and carb. Unknown compression and cam, but “sounds” smooth. I run 16° initial and 36° total all in at 3k rpm. My vacuum can is ported.

I did have a slow crank when hot. I replaced the starter with a high torque mini and 1/0 battery cables. Starts like a champ now!