running dual carbs

[jason nv]

ok i know im beating a dead horse here but should i run the vaccum line from the dist. to the front or rear carb or to the manifold its self where the vaccum line for the wipers go?

[Mike in AZ]

pretty sure it's manifold vacuum....Mike

[JWL]

What year engine/distributor is being discussed?? It does make a difference.

[Bruce Lancaster]

In fact, a huge difference!

[jason nv]

sorry guys its a 1951 8ba with stock dist. i should have said that.. lol

[1952henry]

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Originally Posted by jason nv

sorry guys its a 1951 8ba with stock dist. i should have said that.. lol

Then, to the carb port. Some say there won't be enough vacuum, others say it will work. I'm sure others will chime in.

[Ol' Ron]

The stock dist. didn't work well when new and adding aaaaaaaaaanother carb to the ols system doesn't help much. You can do two things. Buy a new dist with machanical & vacuum adv., Or, Make the rear carb a fake so it doesn't have any affect on the ignition system.

[texcarguy]

I have the same carb setup and engine. Never could get the thing to run worth a damn until I threw the stock distributor in the trash and replaced with a Mallory mechanical advance dual point distributor (not electronic). Now my advance is perfect and the car runs great.
I'm running a progressive throttle setup with blocked idle port base on the secondary carb. Easy to tune and setup, and runs great.

[jason nv]

well i have a chevy dist. machined to fit my flathead. i guess ill run that.. i just suck at dealing with distributors.. and timing.. lol

[36tbird]

You'll like the Chevy, I'm betting. I have one of GMC Bubba's in my 8BA, mechanical advance with a Pertronix. Timed it to maximum vacuum at idle then retarded it just enough for one inch of vacuum drop. It is running great. However, I am building another Chevy distributor with a Pertronix and an adjustable vacuum on it. I figure that there are more adjustment springs available for the Chevy and with the adjustable vacuum, I can play with it to see how if that works.

[flathead4rd]

Do not connect to manifold vacuum, only use the ported vacuum off of the carb. It is my understanding that trying to use the ported vacuum on a dual carb setup does not work properly and most change the dizzy to a full mechanical advance one.

[36tbird]

What if manifold vacuum is all you got, e.g. strombergs? I'm assuming that manifold vacuum is slightly less than ported. Can the reduced vacuum be mitigated with an adjustable vacuum advance set to the lowest setting?

[jason nv]

Originally Posted by 36tbird

You'll like the Chevy, I'm betting. I have one of GMC Bubba's in my 8BA, mechanical advance with a Pertronix. Timed it to maximum vacuum at idle then retarded it just enough for one inch of vacuum drop. It is running great. However, I am building another Chevy distributor with a Pertronix and an adjustable vacuum on it. I figure that there are more adjustment springs available for the Chevy and with the adjustable vacuum, I can play with it to see how if that works.

my chevy dist is also from gmc bubba. i guess ill hook it up and see how it goes.. im sure ill be back with tons of questions on this one..

[Ol' Ron]

Working on the Chevy dists. I have found that 16* mechanical, all in by 2K and 6* vac. 4* in ital. gives the best of both worlda of WOT and cruse economy. We've been experimenting with advance curves and this combination is a good starting place.

[36tbird]

Ol'Ron, I guess you guys who know what you are doing quantify and check these things on a machine. I only know enough to be dangerous so pardon my questions. Are the springs for the mechanical advance color coded? If so, what does 16* mechanical equate to? If you are using an adjustable vacuum with the allen wrench, how do you know what you are setting it to? Can you check the movement with a vacuum tool and set it for max at whatever your vacuum is at 2000 rpm? And finally, if all I have is manifold vacuum because I am running Strombergs, will that work?

[Ol' Ron]

Buy an advance kit form several outfits Summet has them. Use the black bushing and the lightest springs. Install Vac. adv. Install in engine disconnect Vac, bring engine up to 2k set timing to 20*, that should put initial at 4* depending on winch model Delco dist you have, because they have different adv slots. Nopw using manifold vac. and timing light add vac. this should increase the timing about 6-8 degs.

The problem is you don;t have is you don't have a degrees marked on the crank pulley, This bafacates most people. I f you can remove the pulley you can mark the pullet in 5,10,15,20 25,&30. Measure the diameter of the pulley and divide by 360.

Hope this helps. When building an engine, get the piston to head clarance as tight as you can,40-50 thou. Makes all the difference in the world.

[flatjack9]

Originally Posted by 36tbird

What if manifold vacuum is all you got, e.g. strombergs? I'm assuming that manifold vacuum is slightly less than ported. Can the reduced vacuum be mitigated with an adjustable vacuum advance set to the lowest setting?

If you are talking about an 8BA carb, it not ported vacuum, it is a combination of venturi and manifold vacuum and is less than manifold vacuum. On a modern engine, ported vacuum means it is closed off at idle, other than that it's the same as manifold vacuum.

[36tbird]

Wow, great info. Thank you, Lou

[joe plumber]

I run dual 97's on a 53 flathead and don't have any type of advance .I got rid of the points and went to Petronix electronic ignition and their coil.I also switched to 12 volts. Runs without any problems.Also run an Isky 3/4 cam.I know alot of guys don't like the Petronix set up ,but I have ran this for 6-7 years and swear by it ..JMO>

[flatjack9]

Why in the world would you want to run with no advance?