It doesn't make sense - vacuum advance

[65shelby]

I've got a built '65 289. I'm using the original distributor which has been upgraded to electronic ignition with an Ignitor II. Base timing is 16 degrees. Disti is adding another 22 max. I'm trying to dial in the vacuum advance and when I turn the vacuum adjustment 3 turns from the lowest amount of spring resistance (most advance). The car starts and seems to run fine. If, however, I reduce the resistance even more or turn it all the way to the lightest setting, the car will not start. I have the vacuum advance hooked up to the timed port on the carb. My main question is, I don't understand why the vacuum advance has any impact on the car's ability to start or idle?

In case it matters the motor makes about 13 inches of vacuum at idle. Any help would be appreciated.

 

[brianj5600]

Won't start as in the starter turns to slow? Or the starter spins fine but it won't light off?

 

[65shelby]

The starter spins fine, it just won't fire up. Appreciate any ideas. Thanks

 

[65FBE2]

Something else is happening. If it is truely conected to ported vacuum not manifold, then the advance will have no effect. Check to see if you have spark at the plug. I think something is shorting to ground

 

[rbohm]

the first thing to do is to disconnect and plug the vacuum advance line and set your initial timing at about 10-14 degrees. once you have that done, you can then play with the vacuum advance curve. and i agree that you should be running ported vacuum and not full time vacuum.

 

[66Runt]

Might also check the ground pigtail wire that runs between the distributor body and advance plate. If it's broken, it can cause the symptoms you describe.
Good luck!

 

[htwheelz67]

with a pretty hot motor, I have ran the vac advance to straight manifold vac and set the initial timing higher so that while cranking the timing is retarded but once running inital timing was more advanced which would usually cause hard cranking.

 

[65FBE2]

What?

 

[65shelby]

I just want to add that it has no problem starting up and running well with the vacuum advance adjusted to about 2.5-3 turns from the least amount of spring resistance. It's when I turn the vacuum advance all the way to the least resistance that it won't start up. This is what doesn't make sense to me. The vacuum advance setting should not have any impact on the engines ability to start and idle. It shouldn't even be advancing the spark at start up or idle. But in my case it seems like it does have some impact on the engines ability to start. Maybe it's just trying to tell me that it won't like that much vacuum advance.

 

[65shelby]

htwheelz67 - how can the timing become retarded from the initial base timing by only adjusting the vacuum advance? I don't think that's possible. Vacuum advance only advances timing from the base, it doesn't retard it.

 

[jcode68]

Might also check the ground pigtail wire that runs between the distributor body and advance plate. If it's broken, it can cause the symptoms you describe.
Good luck!

I tend to think this would be along the lines of the problem. When you adjust the Vac Advance using the allen wrench, it's simply moving the plate within the distributor housing. If is moved and hitting this wire, it could cause this problem. I would remove the cap and inspect things, especially while making adjustements. You should be able to find the problem.

 

[bnickel]

I just want to add that it has no problem starting up and running well with the vacuum advance adjusted to about 2.5-3 turns from the least amount of spring resistance. It's when I turn the vacuum advance all the way to the least resistance that it won't start up. This is what doesn't make sense to me. The vacuum advance setting should not have any impact on the engines ability to start and idle. It shouldn't even be advancing the spark at start up or idle. But in my case it seems like it does have some impact on the engines ability to start. Maybe it's just trying to tell me that it won't like that much vacuum advance.

vacuum advance, when connected to a ported vacuum source, will not effect the engine's ability to start at all, it sounds like something is either grounding out (shorting) or going open inside the dizzy when you have the vac adv adjusted like that. possibly the breaker plate or the advance arm is touching a bare wire or pulling a connection loose. another alternative is that the distributor bushing is worn out and causing the the point cam to move and close the gap on the pertronix up to the point where the ignition won't fire. what you need to do is pull the cap and run the advance through the full range of adjustment and physically se what is going on.

my only other though is that you actually have the advance connected to full manifold vacuum somehow and when the advance is turned out all the way you're causing a big enough vacuum leak that the car won't start

 

[65shelby]

Thanks for all the advice. I'll check it out and see what I can find. BTW it's definitely connected to the timed port on the carb. Not full manifold.

 

[bnickel]

i'm sure you have checked that port just to make sure but in case you haven't you should pull the vacuum hose for the dizzy at the carb port and put your finger over the port just to make sure there is no vacuum present there with the engine idling

 

[2+2GT]

I agree with those who recommend disconnection the advance altogether, and trying without.

BTW, this is not how the advance should be adjusted. Find someone who can do your distributor on a Sun machine. Your car will thank you by being faster.