running dual carbs
 

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?

Re: running dual carbs
 

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

Re: running dual carbs
 

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

Re: running dual carbs
 

In fact, a huge difference!

Re: running dual carbs
 

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

Re: running dual carbs
 

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.

Re: running dual carbs
 

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.

Re: running dual carbs
 

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.

Re: running dual carbs
 

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

Re: running dual carbs
 

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.

Re: running dual carbs
 

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.

Re: running dual carbs
 

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?

Re: running dual carbs
 

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..

Re: running dual carbs
 

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.

Re: running dual carbs
 

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?

Re: running dual carbs
 

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.

Re: running dual carbs
 

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.

Re: running dual carbs
 

Wow, great info. Thank you, Lou

Re: running dual carbs
 

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>

Re: running dual carbs
 

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

Re: running dual carbs
 

I'm bettin' Joe means no vacuum. Joe, what kind of gas mileage do you get? I'm running just a single 48 on my 8BA with the Pertronix Chevy centrifugal advance. It runs great but my mpg seems lacking. Haven't made a precise measurement but I think it might be around 10 mpg.

Re: running dual carbs
 

Jack, isn't it true that venturi vacuum increases when throttles open, while mainfold vacuum drops?

Isn't that why the load-a-matic distributor will retard timing instead of advance it when connected to manifold vacuum?

Re: running dual carbs
 

Yes that is true. However this is only during acceleration. It kind of operates like the vacuum retard on the earlier distributor. Once you have reached your desired speed, you back off on the accel pedal and manifold vacuum will shoot back up giving full advance. I don't remeber the specs for the advance curve on the 8BA, but I don't think it takes a lot of vacuum to achieve full advance.

Re: running dual carbs
 

Some after market Strombergs had a vacuum port. If you need one let me know. Also, when you run dual carbs you shouldn't run just vacuum advance from the stock dist. You need to upgrade to an aftermarket dist. with mechanical advance or it will never run properly.

Re: running dual carbs
 

I confused you with my post. I meant that as far as vacuum I have only manifold vacuum available. I currently have a Chevy distributor with only mechanical advance and I'm trying to build one that will have both, mechanical and vacuum.

Is there a boss on existing Strombergs that can be drilled and tapped for the vacuum port yours have? Thanks.

Re: running dual carbs
 

Not6 knowing the difference between running good and running great. depends on what's exceptqble to the driver. We had a 4x4 mu son uses 9n h9s business (Forester). Been running this for 5 or 6 years seemed to run fine. Had trouble with it last month and put it in the shop. The increase in power is hard to discribe. Like putting a blown hemi in your Henry J. If you know what that is.

Re: running dual carbs
 

The base already has the hole drilled and tapped for the late distributor. No extra work required. It's venturi vacuum. I'm leaving in the morning for the Iola car show and won't be back until Sunday. I'll try to take a picture then for you. But the after market Strombergs (some, not all of them) had a vacuum port in the base to use as replacements for the Holley if you wanted that option.

Re: running dual carbs
 

Why is that? It does not make enough vacuum to advance?

On top of that, who makes a decent and affordable mechanical advance distributor for the 48-earlier flatheads (2 bolt style) other then Mallory or MSD?

Re: running dual carbs
 

Or is there a unit to put in the pre 48 to make it mechanical? Rather than having to buy some ugly new dizzy?

Re: running dual carbs
 

Chris, I am not aware of any like that. Wish some enterprising, smart type would make and offer such a thing.

In lieu of that, I just bought one of the 8BA style front covers and bolt on cam gear drive to put on a 59a in order to run a converted Chevy distributor. I found that using early water pumps, there ain't much clearance between the housing shaft back of the fan belt. So, I am messing with a non aluminum Chevy distributor to turn down the housing shaft for some clearance. Also, I am going to have the distributor sit up more for belt clearance under the housing base. This will require making a longer distributor drive shaft rod. I figured the steel distributor housing will have more meat and strength for the extension than an aluminum housing. Pictures later when I try to get all of this together.

If I cannot get adequate clearance on the shaft for the belt from turning it down, I may have to engineer a double pulley for the water pumps. My buddy Kahuna sent me one and it has given me an idea on how to make some double pulleys.

Apologies to the purists for this project.:p

Re: running dual carbs
 

It's venturi vacuum which it what the late dist. uses for advance. They are a replacement for the Holley which was stock on a 49-53 engine. Works just like the Holley except it's a Stromberg.

Re: running dual carbs
 

Chris, are you sure that there is not enough vacuum or just a crummy vacuum advance module on the distributor? I understand the the stock Ford advance mechanism is not so good.

Re: running dual carbs
 

The pre 48 distributor is a centrifugal advance unit with a vacuum brake which was initially used to prevent ping on acceleration. But with todays higher octane fuel is generally not needed.

Re: running dual carbs
 

I



I've used the SBC dist on the early 59 block with the original water pumps and no modifications to the dizzy. Just space the generator aou about a 1/4" had over 70K on the insallatiion before the engine blew.

Re: running dual carbs
 

Really......so do you just block the vacuum hole in the dizzy/timing cover?

Re: running dual carbs
 

I remove the piston from the distributor and block the vacuum hole at the manifold.