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.

 

[thinman666]

65 sporty, I'm not getting any email response notifications from my post so sorry for the delay. The timing is 6 deg.

 

[65 sporty]

Have you checked to make sure that 0 on the balancer is TDC? Roll the engine by hand with #1 with the spark plug out, put a long rod, wire or screwdriver in the plug hole and watch it come up and when it starts to go down, stop and roll it back the other way, it will start to come up again and then go back down. It should be the same distance on both sides of 0. If the balancer is marked this would make it even easier

 

[thinman666]

65 sporty, yeah I considered that as possibly the balancer had slipped. I tried to make a bump stop tool from a drilled out spark plug and I didn’t make it quite long enough to reach the piston so out of frustration I gave that up. I tried using a slender screw driver but the angle of the plug hole made the screw driver lay over too horizontal so it proved to be too inaccurate. I’m still going to try some other way. I hate to be defeated so easily!
When I can confirm that the mark is correct I’m going to check total advance as 7mopar mentioned. That is if I can find out what the total is supposed to be.