Downdraft questions

[Lar in Stanwood]

Just acquired a Burns downdraft manifold for a two throat single carb with a three bolt base mount.

I 'd like to know what carb you guys recommend and what modifications, jet sizes are necessary. I plan on using an electric fuel pump with a pressure regulator. Thanks for the help.

[david b allen]

Use a Holley 94 with 52 main jets, no need of fuel pump,my 29 runs strong with this setup.I am now running a 2110 carb with same jet 20+ mpg.
DAVE

[Lar in Stanwood]

Thamk you. What is a 2110 carb?

[midgetracer]

I run two Stromberg 81 carbs and have great luck. The carbs gave me real fits until I sent them to Jere Jobe at vintage carburation in Sommers MT. Jere worked wonders on the carbs and I can't say enough good things about Jere and his top shelf work.

[31Tudor]

I run one Stromberg 97.

[Lar in Stanwood]

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What size jets did you use in your 97 and did you need a fuel pump/pressure regulator?

[david b allen]

The 2110 is a Holly for a 54-56 y block ford 1and 1/16 inch throat, and has latter nozzles which run more efficient and higher CFM 155 for 94 and 185 for 2110.
I increased the fuel line size 1/4 to 5/16 but you don't have to. I run a stock power valve. The problem with fuel pump it is very hard to regulate to 2lbs
DAVE

[ken ct]

Originally Posted by Lar in Stanwood

What size jets did you use in your 97 and did you need a fuel pump/pressure regulator?

Lar,run a 94 from yrs 39-48 with a PV change to 5.5 and jetting around .044-.045. Jetting is a crap shoot at best but you will be in the ball park,you can go up or down going by plug readings if you have to. ken ct. Yes you will probebly need a FP unless this is a "B" motor with a mech. one.And 1/4" line will feed as many as 3 carbs.

[Jim Brierley]

I would run a 97 as they are less apt to suffer problems from the new fuels. Stock .045 jets are most likely correct for the A engine, and 2 or 3 psi max on fuel pressure.

[mngreen]

Originally Posted by Jim Brierley

I would run a 97 as they are less apt to suffer problems from the new fuels. Stock .045 jets are most likely correct for the A engine, and 2 or 3 psi max on fuel pressure.

I have been using a 97 on a single carb Burns downdraft manifold on my Model B/Cragar OHV equipped engine on my Model A for the last 40 years. I didn't know until just recently that my 97 was using stock jetting (#65 power valve, #45 main jets; Thanks Jim Brierley). I could probably run bigger jets in my setup but it has been okay so far! I would think you should do fine with the stock jetting in a stock Model A. You probably will need a fuel pump to feed the 97 even with the cowl mounted gas tank as the angle between bottom of tank and carb may be quite small causing fuel starvation on hills or fast runs.

[ken ct]

This is from my experance with guys ordering parts for these biger carbs for model "A"'s Never any complaints about choices. OMO .Do what ever you feel is right. ken ct.

[31Tudor]

I have the stock jets in my 97 (.045). I was running a fuel pump at first but after going through 2 of them, I gave up and I am now just gravity feed. I have plenty of power and speed. If I am below a 1/4 of a tank, then I will notice that I start to starve for fuel if I am running faster.

[Dave in Boise]

I am thinking about rebuilding a Holley 94 I have.

I like Ken's kits he has, but am curious if anyone has had experience with an adjustable jet set that I had seen on other sites? It appears that it is a large jet with an adjustable needle valve that can meter the flow simulating various jet sizes (like a GAV sort of?)

Might eliminate the need to guessing jet sizes, especially if you travel in different altitudes as well as making changes to the setup of your motor? Looks to be a setup that you make jet adjustments on the outside of the bowl via screws in the bowl plugs?

Perhaps a mix of Kens kit and the adjustable jets might be a good combo?

- Dave

[Phred]

My two cents, speaking from experience on the 97 carb: In theory, the adjustable jets are good. Minute and infinate adjustments can be made without having to remove jets or drain the bowl.

In reality, there is no direct correlation between the number of screw turns and a jet "size". It is very easy to get adjusted "too far" and then not know where your baseline was. Of course, if you have an air/fuel ratio gauge set up on your engine, seeing results would be easier. It is very easy to change jets on the 97 and be back at a known baseline.

Others may have had different results.

Hope this helps. Peace.

[pick]

I'm running twin 97s with adjustable jets. Works great. Can be infinitely fine tuned. as far as a "bench mark" setting, just keep written records of how many turns & the results/conditions etc. I keep mine in the tool box for reference. I did really screw the settings up once trying to tweak it for a hill climb. But once it was dialed back in, I haven't changed a thing in nearly two years of all kinds of driving. Must have gotten "the set up" right.....

[MurphyJ]

I have thought for a long time about converting to a downdraft carb and manifold setup. Can someone provide me with the benefits of such a conversion please? Better mileage, engine performance, etc? Difficult conversion? Many thanks.

[Jim Brierley]

Murphy, A few years ago they were running 2 hill climbs per year in Auburn, CA. I first ran it with a stock C (yeah I know but everyone knows what that is) engine. I then changed to a Winfield 6:1 head and my time improved a full second. I then changed to single Stromberg 81 (from the stock A) and the time improved another full second. At the following climb I changed to a 97 and picked up about 3/10ths.

[Lar in Stanwood]

Just wanted to say thank you gentlemen. Excellent information. I will look for a 97 and go from there. Lar