The Ford Barn

36tbird · 10-31-2014, 08:33 AM

Yo Jim,
Got one of your Chevy units in my 8BA with a Petronix and it has been working great for about 3 years now. My mileage, however is in the 11mpg range and I thought I would try to improve it by putting on a Accel adjustable vac. can. So, I did that and I followed their instructions of backing it counter clockwise (CCW) all the way down initially. Started it up and it ran just as it has so I assumed that was making the can the least sensitive to vacuum as a starting point. Next, I turned the hex adjustment 4 turn CW and took it out yesterday for a drive. It seemed to cruise a bit smoother and be a little more responsive to pedal changes at cruise. Anyway, I was just wondering if the adjustments to these cans on your distributors are standardized enough that you may have seen a good set up and if the springs you send out with your dizzies should be modified with the addition of a can.

Description of the engine: 239, .060 over, 3/4 cam, Offy 3 X 2 with a 48 in center and front and rear 97's blocked off, vacuum is from heater vacuum plate under the 48. The 48 has .043 jets and 69 power valve.

Thanks in advance (get it?)

Ol' Ron · 10-31-2014, 03:17 PM

When using a converted SBC dist with Vacuum advance. I have set the machanical adv to stop at 16 degrees at 2000 RPM and the vacuum advance at 8 degrees. You have to change the advance bushing and springs to do this in the older Bubba distributors, but I inderstand the new ones have adj mach advance modifications. Not sure of the springs. With this set up 4 degs of inital will give 20 degs at 2000 At WOT. and 28 degs at cruise. As far as jetting the carbs, I'd refer to an AF meter. Tuning a 3 carb intake takes some thought work as it's pretty easy to make then drive nice, but difficult to get good mileage at the same time. I'm going through that right noe with one 49 in the center and 2 97's on each end. Still have some putzing to do. You might have Bubba go through your dist again.

BUBBAS IGNITION · 10-31-2014, 05:25 PM

I defer to Ol Ron and Richard for the vac set up....Richard has done a ton of work on the vac part set up for the flathead.....

36tbird · 11-01-2014, 08:42 AM

Thanks Ron and Bubba.

I may not be able to do everything scientifically. Mostly I am using "seat of the pants" quantitative analysis. Ron, I am only running off of the center 48, the outside 97's are blocked off air and fuel wise. The jetting I am using is as recommended by Uncle Max that I did a while ago and it helped out a lot. The stock 48 jets and PV were way too rich.

So, I added the vac can and set the previously only mech. adv. distributor back in with the same initial advance, about 8. Then like I said, I turned the allen head adjustment 4 turns CW from all the way CCW starting point. What I've noticed so far is that slamming back to idle from cruise used to cause a bit of stumbling as the engine searched to stabilize, maybe 600 to 800 rpm. Now when I do that, it drops to a steady 800. In a cruise, the old car just feels stronger. I have not read my plugs yet, I will do that soon to see what is going on there. I am going to rework my exhaust where I may be able to add bungs for an A/F sensor and then I can try to be a bit more scientific.

BUBBAS IGNITION · 11-01-2014, 10:21 AM

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Looks like ya got it.....
The vacuum advance is a "overlap" from mechanical.

Once the engine starts the engine vac is high and gives you lets say 16 degrees advance from the vacuum unit.

Then when you load the engine the vacuum goes down and the advance comes from the engine rpm increase and lets say thats also 16 degrees.

So between the two you have a pretty perfect world.

xx amount of timing all the time .
The vac can be as much as 2-3 mpg as well.

10-31-2014, 08:33 AM	#1
36tbird Senior Member Join Date: May 2010 Location: nw SanAntonio, TX Posts: 939	Bubba Chevy dizzy with vacuum Yo Jim, Got one of your Chevy units in my 8BA with a Petronix and it has been working great for about 3 years now. My mileage, however is in the 11mpg range and I thought I would try to improve it by putting on a Accel adjustable vac. can. So, I did that and I followed their instructions of backing it counter clockwise (CCW) all the way down initially. Started it up and it ran just as it has so I assumed that was making the can the least sensitive to vacuum as a starting point. Next, I turned the hex adjustment 4 turn CW and took it out yesterday for a drive. It seemed to cruise a bit smoother and be a little more responsive to pedal changes at cruise. Anyway, I was just wondering if the adjustments to these cans on your distributors are standardized enough that you may have seen a good set up and if the springs you send out with your dizzies should be modified with the addition of a can. Description of the engine: 239, .060 over, 3/4 cam, Offy 3 X 2 with a 48 in center and front and rear 97's blocked off, vacuum is from heater vacuum plate under the 48. The 48 has .043 jets and 69 power valve. Thanks in advance (get it?)

10-31-2014, 03:17 PM	#2
Ol' Ron Senior Member Join Date: May 2010 Location: Chester Vt Posts: 8,857	Re: Bubba Chevy dizzy with vacuum When using a converted SBC dist with Vacuum advance. I have set the machanical adv to stop at 16 degrees at 2000 RPM and the vacuum advance at 8 degrees. You have to change the advance bushing and springs to do this in the older Bubba distributors, but I inderstand the new ones have adj mach advance modifications. Not sure of the springs. With this set up 4 degs of inital will give 20 degs at 2000 At WOT. and 28 degs at cruise. As far as jetting the carbs, I'd refer to an AF meter. Tuning a 3 carb intake takes some thought work as it's pretty easy to make then drive nice, but difficult to get good mileage at the same time. I'm going through that right noe with one 49 in the center and 2 97's on each end. Still have some putzing to do. You might have Bubba go through your dist again.

10-31-2014, 05:25 PM	#3
BUBBAS IGNITION Senior Member Join Date: May 2010 Location: SPEEDWAY INDIANA Posts: 4,148	Re: Bubba Chevy dizzy with vacuum I defer to Ol Ron and Richard for the vac set up....Richard has done a ton of work on the vac part set up for the flathead..... __________________ If it Makes Spark, we do it !!!! www.bubbasignition.com [email protected]

11-01-2014, 08:42 AM	#4
36tbird Senior Member Join Date: May 2010 Location: nw SanAntonio, TX Posts: 939	Re: Bubba Chevy dizzy with vacuum Thanks Ron and Bubba. I may not be able to do everything scientifically. Mostly I am using "seat of the pants" quantitative analysis. Ron, I am only running off of the center 48, the outside 97's are blocked off air and fuel wise. The jetting I am using is as recommended by Uncle Max that I did a while ago and it helped out a lot. The stock 48 jets and PV were way too rich. So, I added the vac can and set the previously only mech. adv. distributor back in with the same initial advance, about 8. Then like I said, I turned the allen head adjustment 4 turns CW from all the way CCW starting point. What I've noticed so far is that slamming back to idle from cruise used to cause a bit of stumbling as the engine searched to stabilize, maybe 600 to 800 rpm. Now when I do that, it drops to a steady 800. In a cruise, the old car just feels stronger. I have not read my plugs yet, I will do that soon to see what is going on there. I am going to rework my exhaust where I may be able to add bungs for an A/F sensor and then I can try to be a bit more scientific.

11-01-2014, 10:21 AM	#5
BUBBAS IGNITION Senior Member Join Date: May 2010 Location: SPEEDWAY INDIANA Posts: 4,148	Re: Bubba Chevy dizzy with vacuum Sponsored Links (Register now to hide all advertisements) Looks like ya got it..... The vacuum advance is a "overlap" from mechanical. Once the engine starts the engine vac is high and gives you lets say 16 degrees advance from the vacuum unit. Then when you load the engine the vacuum goes down and the advance comes from the engine rpm increase and lets say thats also 16 degrees. So between the two you have a pretty perfect world. xx amount of timing all the time . The vac can be as much as 2-3 mpg as well. __________________ If it Makes Spark, we do it !!!! www.bubbasignition.com [email protected]