218 w/ dual carbs - what size jets?

[plymouth49]

What size jets are recommended as a starting point for dual single-throat Carter Ball & Ball carbs mounted on an Offy manifold on a otherwise stock 218 engine?

[greg g]

stock

[James_Douglas]

Usually with multi carb set ups you need to increase jet size to make up for the loss of vacuum signal due to the increased venturi area for the same amount of cubic inches.

...James

[kevinanderson]

Can you cheat and just the run the carbs a little rich

[Normspeed]

You could just go ahead and install the stock carbs and see how you like it. If it seems too rich for you, you can always round up some different jets. I run stock jets on the same setup, with a slightly modified 218. It has a reground cam and lower restriction exhaust. Seems to run pretty good.

I do run my accelerator pumps at the shortest stroke setting because it seems like a double shot of gas every time you move the gas pedal is a bit more than my motor needs.

[plymouth49]

Hmmmm - I can see using stock jets as a starting point.

I don't understand why you would run richer jets. Each carb only sees itself; vacuum signal (in actuality, the amount and speed of the air flowing thru the venturi) is governed by the throttle plate. If you need, say, 50 BHP at any point in time, that might be from x amount of throttle opening with one carb, or slightly less with two.

I have a Buick 322 with triple Stromberg 97s. It requires several size smaller jets in order to run at the right A/F ratio.

My motor is stock, so there is nothing (like reground cam or larger displacement) to make it flow more air. Running the smallest amount of accelerator pump makes perfect sense. If the engine has a flat spot on acceleration this is easily opened up.

I suspect I will need smaller than stock jets. Does anyone know which sizes I should be looking for? And, where can I get them?

Thanks!!

[Normspeed]

I believe a fella named George Asche sells them, and also knows quite a bit about multiple carbs on old Mopars. He's not online but someone here can probably post a phone number for George.

[Frank Elder]

Don knows!

[Don Coatney]

It is my understanding that the jet size in B&B carburetors is fixed at the

factory. In order to alter the jet size you must solder the hole closed and

re-drill to your specifications. I am running stock sized jets in my dual B&B's

with no problems. I have a long block Desoto engine with a lumpy camshaft

and dual exhaust. I did add double aftermarket air cleaners for beather

engine breathing. I was running a bit rich with single air cleaners. This is

a George Asche modified stock manifold setup.

[martybose]

Well, Don, I sure hope that you've already fixed the fuel leak at the rear carb inlet that is leaving stains all the way down onto the intake manifold!

Marty

[Normspeed]

I don't know, Marty, I run B&Bs too and seems like leaking is the true test of authenticity for a B&B.

[James_Douglas]

I fail to understand how people think that by running two carbs that the engine will run richer. Please folks read a good book on how a carburetor works!

The amount of fuel drawn through the carb is related to total venture area. If you INCREASE the area by adding more carbs your vacuum signal goes DOWN and the amount of fuel pulled by each carb into the engine goes DOWN and thus multi carb engine tend to run LEAN unless you make the jets LARGER.

Sometimes the mythology is hard to kill.

James

[claybill]

the good thing abut the b and b's and offy intakes..

i have been using everything stock on 3 cars for 7 years!!! all is fine..just read your plugs often and set mixture. there is plenty of 'jet' there, enough gas. all mine ran a bit rich at first.

bill

awhile back someone posted that they even cut the mixture all the way back on one carb....a year ago, i think.. i tried it............

[Normspeed]

Heck I hope my 218 doesn't get wind of all that carburetion theory stuff. Might not run right.

I'll stick with the mythology James, silly me.

I fail to understand how people think that by running two carbs that the engine will run richer. Please folks read a good book on how a carburetor works!

The amount of fuel drawn through the carb is related to total venture area. If you INCREASE the area by adding more carbs your vacuum signal goes DOWN and the amount of fuel pulled by each carb into the engine goes DOWN and thus multi carb engine tend to run LEAN unless you make the jets LARGER.

Sometimes the mythology is hard to kill.

James

[James_Douglas]

Norm,

I must respectfully disagree with you.

If you stick two carbs on an engine that are both larger enough relative to what came with it and/or two with a smaller venturi area then...you get the necessary larger jet area and or draw with them.

No doubt that some thing like that is causing more draw and/or more jet area and that is why it "happens" to work fine on your car.

Particularly on carburetors, you cannot get around the physics of the venturi and jets. You just got lucky.

What I don't like to see happen on this site is information that is misleading or not complete.

Many younger people come to this site looking for help and knowledge. Passing on wives tales does them harm in the long run.

Something may in fact "work" in a particular instance, but that does not mean it is technically correct and that it will work in all instances.

We have a duty to understand why something works, or does not, and pass that along so that when someone is working on the next project they understand and can apply the concepts and not just sit there saying to themselves, "...well it worked the last time, I don't know why it is not working on this car".

I will stick with using the same science that the engineers used when they built our cars when I go about modifying them. Because when I do that it--- it works out fine every time on every car.

James

[greg g]

Also I wonder about how you go about adjusting the mixture. The mixture is set by the air flow and the jut size. Unless you physically alter the jet and or venturi area, you can not affect the running mixture. the only adjustable point on the

B1B carb is the amount of air introduced intot he idle circuit. Once the trottle plate is opened, the idle circuit is by passed and no amount of adjustment on the screw will effect how the engine runs.

The only stock carbs that i know of that have jet adjustments are SU's Strombergs, and some high performance Holleys. So please explain how you are adjusting the runnig mixure.

[Normspeed]

To each his own James.

Regarding misleading information on this forum, as with most forums, yes, there is a blend of correct and incorrect info. Also, there may be more than one approach to problem solving, and one should not automatically believe that their own approach is the only correct one.

I would hope that anyone gathering information off the internet would not be so naive as to think everything on a website is "gospel"

Greg, I agree, the only mixture adustment screw on a Ball & Ball affects only the idle circuit. Once you're at operating speed, that adjustment has little or nothing to do with operating fuel air mixture.

[Fluid drive]

The way that all of us old guys used to "jet" a dual set up was by dividing the stock jet size in half and instaling a jet that size in each carb. Unless you are running one of the carbs -like a stromberg- that has adjustable main jets you have to change the fixed type jets. The way to tell when you have achieved the right mixture is by checking the plugs to see if the color is right. Should be a light brown deposit. Wrong mixtures can burn valves or flood cylinders with too much fuel which can cause piston damage.

[LAKOTA169]

What is the "real" advantage of a dual carb setup on a stock 218, other than looking "cool" (which I like)?

Any difference between:

Two 1 barrel carbs (B&B's)

Two 2 barrel carbs

One 2 barrel w/adapter on stock manifold.

I like the dual carb look and have been wanting to do it, but right now car needs more important things like kingpins and brake work. I really like the pictures of your engines (also makes me depressed that mine doesn't look like that )

[Normspeed]

For me it's mostly the look. But it does run pretty well, very reliable and I can get 20 mpg or more on the open road using OD. Around town, more like 12-14.

[Don Coatney]

The way that all of us old guys used to "jet" a dual set up was by dividing the stock jet size in half and instaling a jet that size in each carb. Unless you are running one of the carbs -like a stromberg- that has adjustable main jets you have to change the fixed type jets. The way to tell when you have achieved the right mixture is by checking the plugs to see if the color is right. Should be a light brown deposit. Wrong mixtures can burn valves or flood cylinders with too much fuel which can cause piston damage.

Fluid drive;

Interesting information. How about a bit of profile information so we know whom you are, where you hail from, and what cars you have? This information will go a long way in giving yourself credit for your statments.