Bing Carburetors #3
What's The Difference?
by Alan Buehner
Originally printed in the 2006 issue #31 of Still….Keeping Track
The purpose of this article is to show what the differences are between the Bing carburetors used on the Penton motorcycles from 1968 thru 1975 and the internal parts used in them. To simplify things for this article, I will be comparing the Bing 27, 32, and 36mm carburetors. Many of the parts used on the Bings are consistent and are interchangeable. These parts include: float bowl gaskets, floats, carb bowl clamp screws, idle adjustment screws, throttle stop screw, top cover screws, cable adjustment screws, pilot jets, main jets, and jet holders.
Consult the specifications in the Penton Owners Manuals for suggested sizes for needles and jets in setting up a Bing carb. Check the Penton Parts Lists for the Penton part numbers and Bing interchange part number for any Bing parts.
Bing carburetor bodies
As can be seen from the above photo, Bings can be easily identified by size when compared to one another however, the bodies are deceiving in that each body size was used for more than one size by enlarging the intake bore. The 27mm above could also be a 24mm or 26mm. The 32mm above could also be a 28mm or 30mm. The 36mm above could also be a 38mm. The best way to verify the size is to check the model numbers stamped on each carb. Example: 1/36/103 = 36mm (the number between the 2 slash marks). NOTE: the 38mm carb models and some of the 36mm use a float bowl with an extension on the bottom for the main jet (see arrow).
Bing covers & springs
The covers on the Bing carbs are distinctly different in size. The 32mm and 36mm sizes shown are set up with only one adjustment screw for the throttle. Most of these are set up with another adjustment screw for the choke cable.
The springs for the throttle valves are different in lengths and also diameter of the windings in order to fit inside the throttle valves.
Bing internal jets
Items “A” are needle jets. They are not interchangable, and as can be seen, are different in the length of their lower bodies. Sizes are stamped on the side.
Items “B” are the jet holders. They came in 2 different styles and are interchangeable.
Items “C” are the main jets. They are interchangeable and come in wide selection of openings from size 80 thru 200 as engraved on them.
Items “D” are the Pilot jets also known as idle jets. These are interchangeable. Sizes are engraved on the side of the screw heads.
Bing slides & needles
The Bing throttle slides (C) are differ-ent in length and diameter as shown. They are available (A) with or (B) without cut-outs to accept choke air valves (slides F).
Needles (D) are different in length. Sizes are identified by the number of rings (1, 2, or 3) on the needle just below the adjustment slots.
The Bing 24, 26, &27mm carbs have a side choke assembly that use a starter slide and sleeve (E).
The Bing 32 & 36mm carbs use a choke slide (F) that fits in the slot of the throttle slide. The choke slides and springs are of different lengths. These chokes are not necessary for starting a bike and it is common to find them missing.
Bing floats are interchangeable They came in three different styles: white styrofoam, yellow plastic with a sealed air chamber, and black styrofoam.
A Doug Wilford tip for Bing Carbs
To remove the old float needle seats, tap the opening. Leave the tap in place, heat up the carb body, and use the tap as a tool to pull the old seat out. While the carb body is still warm, insert the new float needle seat.
On Bing 24, 26, & 27mm carbs with side chokes, make sure that the starter slide (item E) is installed in the carb and that it still has the wax sealing material inside it. If the starter slide and it's wax is missing, the engine will start but it will run rich as the engine warms up.