ignition timing , 1956

[TedRamAir2]

I have a customer with a 1956 312, AT. I replaced the original vacuum advance with a rebuilt unit. When setting the timing, should both vacuum lines be off? what do I set it to? the owner does not have a service manual. I really need him to get one! it also has a off idle stumble, like it goes lean for a time, then as the throttle is opened wider, smooths out. The accel pump is working. TIA Ted Schore, Ocala Fl

 

[paul5456]

Both lines must be off and as you know, plugged..

What are you setting the initial advance it. The factory setting is 3 or 6 degrees but most yblocks run better at 10-12 degrees without any pings. This higher setting my help the off idle hesitation.

 

[Shawnski]

Both lines must be off and as you know, plugged..

What are you setting the initial advance it. The factory setting is 3 or 6 degrees but most yblocks run better at 10-12 degrees without any pings. This higher setting my help the off idle hesitation.

If your customers engine still has the Holly Tea Pot 4v, there’s valve that is likely worn or leaking bye.

70-45 Holley 2140 4000Diaphragm Gas Enrichment Valve - 70-45

 

[Shawnski]

If your customers engine still has the Holly Tea Pot 4v, there’s valve that is likely worn or leaking bye.

70-45 Holley 2140 4000Diaphragm Gas Enrichment Valve - 70-45

This valve takes over just after the accelerator pump and before the secondary starts to pull in…

 

[TedRamAir2]

This valve takes over just after the accelerator pump and before the secondary starts to pull in…

That has been replaced, so I ASSUME its working. Seems like I tested it a while back, and the diaphragm held vacuum ok. Thank you very much. I will get the timing adjusted, and see what happens!!

 

[TedRamAir2]

This valve takes over just after the accelerator pump and before the secondary starts to pull in…

I checked that diaphragm it moves and will hold vacuum. pulled the Power Valve out, it works. Small hole will pass air when the valve pin is down. that's a small hole!.

 

[Frankie the Fink]

Both lines must be off and as you know, plugged..

What are you setting the initial advance it. The factory setting is 3 or 6 degrees but most yblocks run better at 10-12 degrees without any pings. This higher setting my help the off idle hesitation.

Any American engine I know off requires plugging the vacuum advance to set initial timing. And yes the factory timing map is set very conservatviely for different gas formulationa, altitutdes and driveing styles. Bumping up the timing is a cost-free, seat-of-the-pants perfromance increase in nearly every case.

 

[cokefirst]

Yes, the vacuum advance needs to be disconnected to set Initial timing. Agree with the 10-12 instead of the 6 degree spec for auto trans cars. check that power valve and the accelerator pump. I would get an accelerator pump from Casco or any supplier that an assure you that they are good for alcohol blended gasoline.

 

[Ward 57]

My vacuum advance is hard wired so I'm not breaking that connection to time. At idle it doesn't have that much influence anyway. It's a driver so max performance is not a goal and just great torque and the howl tone of the carb and rumble of the exhaust when you step on it is just music.

 

[cokefirst]

your vacuum advance should not be "hard wired" but should have a fitting that you can unthread at either end of the two hollow metal vacuum lines.

 

[Ward 57]

your vacuum advance should not be "hard wired" but should have a fitting that you can unthread at either end of the two hollow metal vacuum lines.

True but I'm not breaking them for this. Have never had an issue when timing. If the slight vacuum advances it at idle there is no harm in advancing it a bit more anyway. It's a dance.

 

[cokefirst]

Be sure and check the diaphragms from time to time. The double diaphragms in that distributor is designed to advance the spark at speed and to retard it on deceleration.