Ignition Timing ?

[tatat]

Hi guys
I have a piggie with a 2 f engine and a holly carb.
I have set the ignition timing with a light, have set the mixture screws with a vacuum guauge .
On the carb there is a vacuum advance timing port. On the intake manifold there is a vacuum port.
On thevacuum port of the carb carb at idle, no vacuum. Only vacuum when the revs are higher. On the manifold at idle 23 Hg mm of depression. If I plug the hose on the intake manifold it will advance the timing . If I plug it on the carb, no advance port am'I supposed to use.?
When I bought the piggie it was connected to the intake manifold but I moved the distributor for more or less advance to try to get the good timing so I loose al reference.
On a oem carb, at idle, does'the vacuum port for the distributor give vacuum or not aat idle? In other world, is your timing set on 8degrees btdc at idle, connected to your vacuum hose?

Thanks for yours answers
Regards

 

[Pighead]

Use the carb vacuum port. I disconnect the dizzy vac hose when setting timing.

 

[tatat]

Ok. That's what I did. Disconnected the hose during the timing setting.
Thanks.

 

[Splangy]

It’s normal to not see vacuum at the ported carb vacuum advance port at idle. Like pighead said, that’s the proper place for it.

 

[Dizzy]

If your Holley was not jetted for the 2F, or you are running it at an altitude significantly dissimilar from how it was intended, then your vacuum gauge is the wrong tool. You need an O2 sensor in your exhaust and a Air Fuel ratio display for a wider range of tuning. An O2 bung can be a drill-and-clamp, but most are drill and weld. Or, you need someone to tell you how it should be jetted based on a similar build. Generally, you can use your ear to get an idle by closing the idle speed screw to a minimum smooth idle and then the idle mix closed to a maximum and you are gold. If you 'read' your plugs (looking for carbon=rich, or super white insulator=lean) at a range of throttle positions you might be lucky and 'wing it' and not get an O2 sensor and A/F ratio meter.

Many folks run 10 deg btdc at idle on desmog jobs and let the mechanical advance, and possibly lower octane fuel, do the work. 'Ported' carb vacuum is what many use for the distributor. Otherwise, a 2F from factory would have had 'ported' vac running to a Vacuum Switching Valve then to the distributor. So, If the distributor was hooked up to the intake manifold, then I suspect that jetting might also be an issue.