Dual carb intake

[tbirdtbird]

go for it!
The Vortex is similar to what Purdy did, look at post #2. I grabbed a Vortex from Snyder. But I am running a side mount oil filter so I don't think I can make it work, (Purdy you warned me), but at some point I'd like to figure a way to make it all work. In the mean time I am almost done installing a Bill Stipe IB330 .330 lift cam. I have installed a couple of these and you really wake the engine up without having crappy low speed performance. The motor just wants to go instead of laboring to get anything done.

BTW the Vortex comes with all the linkages you need

[Gabalus]

Thank you tbirdtbird.

I'm a little bit "afraid" by all these changes.
With my model B engine ( model b cam and ports), it probably run well.
I've got also an very old HC head (7.5:1) but I'm not sure I put it on. I suppose it should be too strong.

I would like to know if the set-up is difficult ( need to change jets, fixed the second gav ?) ? And mileage ? Start ? ...
Thank you.

[Purdy Swoft]

A remote oil filter would be worth the expense, you could then run the Vortex setup and sell the valve cover filter setup.

Actually you get two linkages with the Vortex manmifold, one for the throttles and another for the chokes. I feel that choking two carbs is too much. I only choke the front carb and ended up with an extra linkage.

[jhowes]

I'm running the vortex updraft model also and it works great. The tilly or marvel carbs work best, for some reason the zenith's just don't. Power is good, looks period correct, or cool. And one carb has no gav adjustment. Jack

[Purdy Swoft]

Originally Posted by Gabalus

Thank you tbirdtbird.

I'm a little bit "afraid" by all these changes.
With my model B engine ( model b cam and ports), it probably run well.
I've got also an very old HC head (7.5:1) but I'm not sure I put it on. I suppose it should be too strong.

I would like to know if the set-up is difficult ( need to change jets, fixed the second gav ?) ? And mileage ? Start ? ...
Thank you.

Not Tbird, but the setup is as easy as it could possibly get. I use swap meet carbs that I cleaned up and use original Jets. The rear carb GAV remains closed at all times. If you run B carbs both GAVs will run closed after a brief warm up. I get better gas milage with dual B updraft carbs on my cast iron Trojan and Uni-Flo manifolds than I do with a single model A Zenith carb . With one carb mounted to the intake at the port for the front two cylinders and another carb at the port for the rear two cylinders , you get better distribution of the fuel, its closer to direct port induction than the side by side setup . The engine runs smoother and doesn't have to suck as hard to get the fuel where it needs to be for best power. Unlike dual down draft setups, you won't need a fuel pump or fuel pressure regulator. Dual updrafts are not as sensative to jet size as downdraft carbs. The manifold is open plenium and it probably wouldn't matter if the jet sizes were different. The Vortex manifold has model A size runners and the larger venturi size of the B carb is really of no benefit with the Vortex manifold . Dyno tests showed no difference in horsepower, whether model A Zenith carbs or model B Zenith carbs were used. My thought is that the Model A size runners will only flow so much unless they are opened up. I feel that with an aluminum updraft manifold that lighter carburetors would be better to avoid warpage at the flanges from the weight of a cast iron carburetor. I feel that because of weight and float setup that Tillotson model X or Marvel carbs would be a good choice for the Vortex manifold. Because of simplicity a pair of GOOD marvel carbs may be the better choice.

As for heads and compression ratio , don't expect much boost, no matter what you do without better combustion chamber design and higher compression than the original head can give . For driveability, its best to not go much over six to one. Higher compression such as seven to one or higher will give more power but timing knocks and having to drive with one hand on the spark lever to try and handle the knocks will take most of the fun out of driving. If compression is over six to one, it would be best to run a centrifugal advance distributor.

[Gabalus]

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I read that Tilly needs lot of work before running well. Is it true ?
I read somewhere that I need to take the second carb choke of. It's a mistake ?
And gas mileage ? Do you have an idea ?

[Gabalus]

Thank you Purdy ! It's clear.

Is it difficult to adjust linkages ?

[modelAtony]

Originally Posted by Gabalus

I read that Tilly needs lot of work before running well. Is it true ?
I read somewhere that I need to take the second carb choke of. It's a mistake ?
And gas mileage ? Do you have an idea ?

I have always had better running with Tilly and so have many of my friends. have fun modelAtony tony white Lafayette, LA

[ABento]

I notice that most here seem to be running the carbs together and only one with the progressive linkage set up,I would think that the progressive would be the way to go but would there be a difference because of one carb further ahead on the manifold cause a mixture problem.

[Purdy Swoft]

Here is a pic of the Vortex with Marvels. I haven't tried the linkage yet but it shouldn't be much trouble. The linkage with my Trojan setup was easy enough. The linkage on my speedster with the Uni-Flo intake is home made, It stuck wide open a couple of times before I got it dialed in and gave quite a scare !!!!!!! The throttle levers on both carbs must be at the same angle . Sometimes, over the years the throttle levers on the carburetors have been bent and can cause extra work to make the linkage work smoothly. Its really no big deal.

[Purdy Swoft]

Originally Posted by Gabalus

I read that Tilly needs lot of work before running well. Is it true ?
I read somewhere that I need to take the second carb choke of. It's a mistake ?
And gas mileage ? Do you have an idea ?

Tillotson carburetors can be finiky as hell. The main problem with Tillotson model X and XF carburetors is that they are famous for vacume leaks and will cause backfire when you try to accelerate for that reason . I wouldn't remove the choke from the rear carb . Removing the choke from the rear carb will change the air flow through the throat and cause leaner operation. I just run the choke on the front carb and just leave the rear choke disconnected and the GAV closed. With the choke butterfly and shaft removedwill cause leaner opperation of the rear carb. Removing the choke parts on the second carb has been tried with dual down draft setups and caused a similiar problem. Removing choke parts is a bad idea . Gas mileage improved on both of my cars with dual updrafts.

[Purdy Swoft]

I run dual updraft model B carburetors on two of my model A's . I'm running cast iron dual updraft manifolds with these two model A's . I feel that a progressive linkage setup would be of no benefit . Two original model B carburetors run great together . Mine takes full throttle with no hesitation or flooding . There is no problem with idling . Two carburetors work well for me . For best results with any engine mods , a higher compression head should be the first mod .

I feel that Marvel carbs would probably be a good choice for use with an aluminum intake manifold because of weight . The model B carb is heavier than the pot metal carburetors . Heavy carbs could eventually cause a sag at the carburetor mounting flanges on aluminum manifolds in time . I prefer to use cast iron manifolds with cast iron carburetors .

I have a Vortex dual updraft manifold that I plan to use with Marvel carbs . It has ben said that the Marvel out flows the Tillotson and the model A Zenith one and two carbs .

[Purdy Swoft]

The model B carburetor has a larger throat size than the model A Zenith one and two carbs . The Tillotson and Marvel Carbs have the same throat size as the model A zenith carburetor . Running a B carb on a model A size manifold runner won't give full model B carb performance unless the manifold runner is enlarged to model B runner size . I have bored the older cast iron manifolds to model B size . I have hesitated to bore the runner on my Vortex manifold for fear of weakening the aluminum manifold runner . .

[Gene F]

I had one of the 7:1s on my A once, and you are right. I had to mind the spark advance constantly. The regular Brumfield is just fine

[rmj36109]

Originally Posted by Dave in MN

I have a dual mount manifold that is set up for Zenith A carbs. It may not stand up over time as some suggest but I have to try. The second tube is not cast iron and the components are brazed together. Note the structural web between the two primary passages...
I plan to construct a progressive linkage that brings the second carb on when the first is about 1/2 open. I'm still playing with the sketches for this linkage but should have it worked out before next driving season. Hey...living in Minnesota demands a project or two to keep us sane from November to April!
Good Day!

Update: I purchased this thing on eBay. I was doing the research to obtain the parts to build one and up it popped...so I bought it. If I was building this manifold from scratch, I would use all steel tubing. The carb and manifold flanges are available from suppliers. If this thing cracks...I'll follow my first plan to build one from steel tubing. For my purposes of making the progressive linkage work, it is important that the two throttle shafts are in alignment and this thing is dead on!

Dave, I purchased a running chassis and it has the exact dual carb intake as you photo shows. I have now had the engine rebuilt and wander it this intake will make any power difference. My carb rebuilder says no. What say you? It looks great on the car drawing a lot of lookers. Please email me at [email protected] with any help in coming up with a progressive linkage as I plan to either use it with a blanked off carb or 2 working ones. Call even if you like @334-590-1749 Ron Johnson

[Purdy Swoft]

Without first increasing the compression ratio , most other mods will make very little noticeable difference in performance on a stock model A engine .