Carb Internals

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Carb Internals

Post by m75 » November 26th, 2020, 2:43 pm

On the Zenith 13660, there is an insert in the throat of the carb. Looking past the Choke plate, it might referred to as a venturi, and sits between the choke and throttle plates. Discharge opening of the main well tube protrudes this insert.

Question: Should this piece (venturi, whatever it's called...) have movement? Mine has approx 1/16th in slop and that seems excessive given the delicate nature of these carbs.

Also, is there a difference between carbs (13660 a/b) that is particular to emissions-controlled M151s? My carb only references Zenith 13660, Ord# 11681709, and dated 4 274 (a Julian date maybe?).
Jim Peterson
SGM, 31B Retired 2015
1961 M151 -Sold
1974 M151A2, Working It!

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Re: Carb Internals

Post by Horst » November 26th, 2020, 2:54 pm

the venturi shall not move at all. A small grub screw holds it tight in the carb body. That screw is (as far as I remember not having the manual in front of me) covered by a plastic plug.

1972 USMC M151A2 w/ROPS (ex Barstow) and M416
1962 M201 and trailer
1966 Pontiac GTO
1987 Suzuki Samurai
1987 911
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Re: Carb Internals

Post by rickf » November 26th, 2020, 5:54 pm

Jim, That is exactly what that is, the venturi. As Horst says it is not really supposed to be loose but with that said in all of the carbs I have built I have yet to see one tight. That screw is not really a set screw, it sits in a slot which is more of a locator or positioning slot than a clinching slot. On a spare carb I had I took the venturi out and I carefully molded the seat with JB Weld so that it sat in there perfectly with absolutely no movement and no air could get past it. I had run the carb before and after the modification and there was absolutely no difference. I even went on to port and polish the inlet side of the carb since that was the ongoing rage at the time and everybody said you get SOOO much more power. Yea, right, and those magnetic fuel line doodads work too. :roll: :roll: :roll: :lol: :lol: :lol: No more power at all. No difference in idle either. These carbs run quite well when set up correctly AND when the engine is properly tuned. Everybody seems to miss that last part!

As far as difference between versions, Yes and no. They toyed with changing the main jet in the A version to a 28 from a 30 but it made no difference. The exhaust manifold will limit the amount of air and fuel long before you can utilize the full amount needed even on a 28 main jet. They went back to a 30 main jet on the B version. Guess that says something huh?
1964 M151A1
1984 M1008
1967 M416
04/1952 M100
12/1952 M100- Departed
AN/TSQ-114A Trailblazer- Gone

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