The Ford Barn

38coop · 03-13-2016, 08:08 AM

This question is for the guys using Bubbas chevy electronic conversion distributor. I have a stock 8BA and stock 94 carburetor. Are you using vacuum from the carburetor or intake manifold? I will be starting this engine for the first time before long and this might help. Thanks

BUBBAS IGNITION · 03-13-2016, 08:19 AM

My suggestion would be on a first run, dont use the vacuum advance . Adjust the timing with a light on the pin (frt cover) and start it up. Adjust the idle and air fuel and get a few hours of run time on the engine dealing with all the normal new engine stuff.

Then adjust the vac canister (allen wrench) to max tension (inward) hook the vac to manifold vacuum and go from there adding more until spark knock occurs.

I will get a instruction sheet in the box someday?

Ol' Ron · 03-13-2016, 12:22 PM

Richard wrote a tuning post a few weeks back that explains everything. Remember the Carburetors and ignition systems are tuned for cruise conditions. Most street driven cars spend 90% of the time at part throttle, where the fuel mixture is lean. This requires more advance, which is supplied by the Vac adv. On acceleration the Power valve opens creating a rich mixture and the vacuum advance drops out and only the mechanical advance fires the plugs. Testing as shown that between 18-22 degs advance provides the best powser and 2428 the best economy. You have to consider the Air/fuel ratio as well. 14.7 is the norm in cruise bit 15.5 works very well in a higher compression engine with a lean mixture. However all this depends on the combustion chamber design, where piston to head clearance is the critical factor.
Now aren't you glad you asked??

JSeery · 03-13-2016, 12:43 PM

But in all cases, manifold vacuum! The load-a-matic uses the carb vacuum the others use manifold vacuum.

Ritzy1 · 03-13-2016, 01:01 PM

I've got a vacuum advance question about the earlier 59A motor. I've got a crab style distributor that originally had the vacuum advance line attached to the manifold below the carburetor. I'm going to go with an Edelbrock slingshot manifold and two Strombergs after the rebuild; will I need to plumb the vacuum line from the front cover into the manifold below where the upper part of that manifold joins the base to get the vacuum advance to work properly?

BUBBAS IGNITION · 03-13-2016, 08:43 PM

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Quote:

Originally Posted by Ritzy1

I've got a vacuum advance question about the earlier 59A motor. I've got a crab style distributor that originally had the vacuum advance line attached to the manifold below the carburetor. I'm going to go with an Edelbrock slingshot manifold and two Strombergs after the rebuild; will I need to plumb the vacuum line from the front cover into the manifold below where the upper part of that manifold joins the base to get the vacuum advance to work properly?

Yep , manifold vacuum...

03-13-2016, 08:08 AM	#1
38coop Senior Member Join Date: May 2010 Location: Cocoa Florida Posts: 180	Vacuum Advance This question is for the guys using Bubbas chevy electronic conversion distributor. I have a stock 8BA and stock 94 carburetor. Are you using vacuum from the carburetor or intake manifold? I will be starting this engine for the first time before long and this might help. Thanks

03-13-2016, 08:19 AM	#2
BUBBAS IGNITION Senior Member Join Date: May 2010 Location: SPEEDWAY INDIANA Posts: 4,148	Re: Vacuum Advance My suggestion would be on a first run, dont use the vacuum advance . Adjust the timing with a light on the pin (frt cover) and start it up. Adjust the idle and air fuel and get a few hours of run time on the engine dealing with all the normal new engine stuff. Then adjust the vac canister (allen wrench) to max tension (inward) hook the vac to manifold vacuum and go from there adding more until spark knock occurs. I will get a instruction sheet in the box someday? __________________ If it Makes Spark, we do it !!!! www.bubbasignition.com [email protected]

03-13-2016, 12:22 PM	#3
Ol' Ron Senior Member Join Date: May 2010 Location: Chester Vt Posts: 8,860	Re: Vacuum Advance Richard wrote a tuning post a few weeks back that explains everything. Remember the Carburetors and ignition systems are tuned for cruise conditions. Most street driven cars spend 90% of the time at part throttle, where the fuel mixture is lean. This requires more advance, which is supplied by the Vac adv. On acceleration the Power valve opens creating a rich mixture and the vacuum advance drops out and only the mechanical advance fires the plugs. Testing as shown that between 18-22 degs advance provides the best powser and 2428 the best economy. You have to consider the Air/fuel ratio as well. 14.7 is the norm in cruise bit 15.5 works very well in a higher compression engine with a lean mixture. However all this depends on the combustion chamber design, where piston to head clearance is the critical factor. Now aren't you glad you asked??

03-13-2016, 12:43 PM	#4
JSeery Member Emeritus Join Date: Nov 2012 Location: Wichita KS Posts: 16,132	Re: Vacuum Advance But in all cases, manifold vacuum! The load-a-matic uses the carb vacuum the others use manifold vacuum.

03-13-2016, 01:01 PM	#5
Ritzy1 Senior Member Join Date: Feb 2016 Location: Plymouth, MA Posts: 207	Re: Vacuum Advance I've got a vacuum advance question about the earlier 59A motor. I've got a crab style distributor that originally had the vacuum advance line attached to the manifold below the carburetor. I'm going to go with an Edelbrock slingshot manifold and two Strombergs after the rebuild; will I need to plumb the vacuum line from the front cover into the manifold below where the upper part of that manifold joins the base to get the vacuum advance to work properly?