Distributor vacuum advance

[thinman666]

1969 F100 240ci engine with a new distributor. The engine runs best when the vacuum chamber is disconnected and vacuum line plugged. Would someone offer possible causes? The dwell and the timing is set per specs.. I can't figure this out. Any suggestions will be appreciated.

Thanks,
Russell

 

[65 sporty]

Is the advance connected to full vacuum or ported vacuum? It should probably be connected to ported vacuum, then it only add advance when it off idle

 

[thinman666]

I tried both. Same results.

 

[LocuMob]

Can you adjust it with an Allen wrench through the vacuum port? I had a similar issue with a rebuilt distributor, and it was fine after a quick adjustment.

 

[thinman666]

I'm not sure. It's not a high buck distributor so I assume it's not. I can probably fiddle around with an allen wrench and maybe tell or better yet call the supplier.
I read an article that mentioned carb jetting can have an effect on how a distributor performs. Sounds reasonable since fuel/air/ignition timing is what vacuum advance is all about as I understand. That got me thinking back and if I'm not remembering incorrectly this issue started after I increased the main jet size in the carb but the problem is at and off idle mostly.

 

[65 sporty]

What's your base timing set at?

 

[7mopar]

That what the vacuum advance was added for to prevent. You many have to drop the vacuum required for advance. It's factory setting should be stamped on the mounting flange. Best to use a vacuum pump with a gauge to check the setting.