ignition timing

[sbx22]

350 mild street set-up with Holley 670 street avenger carb

I want to do the ported timing vacuum advance to full manifold advance swap. Right now, I'm having vacuum advance on the distributor hooked up to the ported vacuum.

My question is, do I have to recheck timing? I'm assuming so because, well, now it's full vacuum advance. Anyway, do I check with the vacuum advance hooked up? What's the proper way? Right now, my full mechanical advance is set to 35 deg BTDC.

Any help is appreciated.

[rich weyand]

Nope, just swap the tube and you're good.

Base timing is not set with the vacuum advance connected so it makes no difference to base timing where you connect it.  And 35* BTDC at full mechanical is right in the ballpark.

You will probably have to adjust your idle screw down.  It will like manifold vacuum much better, maybe 150-200 rpm better.

[sbx22]

Awesome. Thanks Rich.

[rich weyand]

No problem.

You're probably going to want to lean out your idle mixture too.  A richer idle mixture burns faster, which helps make up for the ridiculously late spark at idle when running on ported vacuum.  So re-adjust your idle mixture once you get the idle rpms back where you want them.