7RT Carburetor

[waynet]

Hi Folks,

Is there anything special about a 7RT Carburetor and why are they used mainly on pickup trucks? Is it a power or economy carburetor?

[1952henry]

Same as the rest except for the air horn. Oh, and though carrying the 7rt tag, there was an 8RT which had a hand throttle. That, along with the choke, were cable operated.

[ford38v8]

All model 94 carbs were functionally the same. Differences were in how they were controlled, how they were vented, the air cleaner mounting ring, and the distributor vacuum port. Nozzle bar differences didn’t affect functionality. Power valve and main jets were interchangeable, matched to expected operational conditions.

[petehoovie]

Originally Posted by 1952henry

Same as the rest except for the air horn. Oh, and though carrying the 7rt tag, there was an 8RT which had a hand throttle. That, along with the choke, were cable operated.

[waynet]

Ok, so the internals are the same except for the air horn which will accommodate an oil bath type air filter?

[flatjack9]

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Yes

[1952henry]

Thanks, Petehoovie.

[rotorwrench]

The Ford Bonus Built Trucks had the distinction of being the first of the 8BA family to make production in late 1947. 7=1947, R=V8, and T=Truck since those parts were designed in 1947. The distributor is part of the package since the two work together as a Holley designed system. Ford was always changing things so it didn't take long for a change in 1948 (8BA). The passenger cars had different air filters and eventually started to go toward automatic chokes while trucks were still more manual and utilitarian in nature.

[waynet]

Originally Posted by rotorwrench

The Ford Bonus Built Trucks had the distinction of being the first of the 8BA family to make production in late 1947. 7=1947, R=V8, and T=Truck since those parts were designed in 1947. The distributor is part of the package since the two work together as a Holley designed system. Ford was always changing things so it didn't take long for a change in 1948 (8BA). The passenger cars had different air filters and eventually started to go toward automatic chokes while trucks were still more manual and utilitarian in nature.

Interesting...... thanks.

[1952henry]

IMG_0134.jpeg

An 8RT I restored. 7RT body and air horn with cable choke, throttle, and bracket.

[petehoovie]

Originally Posted by 1952henry

Attachment 515699

An 8RT I restored. 7RT body and air horn with cable choke, throttle, and bracket.

[1952henry]

Thanks, again! There is a caveat to parts interchanging; that relates to nozzle bars. The later 7RTs, as well as EABs had the high lift nozzle bars as opposed to the inverted V style. Not a big deal as long as the top has the recess to clear the high lift nozzles.

[waynet]

Could anyone explain how a worn throttle shaft would affect the the tuning on a 7RT/94 carb? Plugs and exhaust always appear sooty black.

[1952henry]

That may be leaky power valve. Worn throttle shaft would create vacuum leak.

[ford38v8]

Originally Posted by waynet

Could anyone explain how a worn throttle shaft would affect the the tuning on a 7RT/94 carb? Plugs and exhaust always appear sooty black.

It seems to me that one would have little to do with the other. The "tuning" of any 94 would consist of the setting of the float, the adjustment of the idle mixture, the setting of the accelerator pump stroke, and the idle speed. Anything else such as the main jet size or the value of the power valve would be determined by application, not adjustable as in tuning. A well worn throttle shaft could lean out the mixture a little, so it may have been called out on a rebuild invoice as required replacement for proper tuning.

[waynet]

Thanks everyone. Looks like a carby rebuild. Any suggestions where to buy a good rebuild kit including replacement throttle shaft?

[1952henry]

Daytona parts for kits. Vintage speed or speedway for shaft. Easy enough to rebuild yourself. Once apart, give it a day or two soak in a closed container of acetone, followed by a good blasting of carb cleaner through all passages.

[waynet]

Originally Posted by 1952henry

Daytona parts for kits. Vintage speed or speedway for shaft. Easy enough to rebuild yourself. Once apart, give it a day or two soak in a closed container of acetone, followed by a good blasting of carb cleaner through all passages.

Thanks for advice.

[38 coupe]

Regarding the first question, a worn throttle shaft allows a small amount of air to leak into the carburetor around the throttle shaft. I have never experienced this having a meaningful effect on tuning, I have always been able to slow the idle down with the idle speed adjustment and smooth the idle with the mixture screws.
If I was attempting to run multiple carburetors I might have a different experience, but have no interest since my stock V8s will run to my speed limits and road handling already (75 mph in central Texas).