Thus as these shaft seals wear and harden, they can't always maintain a vacuum-tight seal in all conditions, resulting in a lean running condition once the engine is warmed up-even though they "seal" perfectly well at idle, or when the carb bodies are still cool. The aluminum-bodied carbs, when heated by conduction from the engine, tend to expand more quickly and by a greater amount than the air-cooled steel throttle shafts. Uses 2 per carb, but without taking the carbs apart from their rack, the only ones you can replace are the outermost seals on the end carbs. NOT: fuel jets, air jets, float valves, and main jet needles are located in the section "LOWER END PARTS" further below.Īaa) OEM and aftermarket Mikuni carb THROTTLE SHAFT SEALS.these are the seals on the outside of the carb body that the throttle shaft passes through.
#MIKUNI BS34 CARBURETOR SERIES#
NOTE: the above link shows the exploded view of the BS28/BS30 series of Mikuni carbs (used on XJ550 and XJ650 Turbo models), the BS33-and-larger series move the pilot air jet from under the vac piston diaphram to the carb throat.and have the choke plunger coming out of the side of the carb body rather than the top. Note that the above link shows the rebuild for the BS28 series of Mikuni carbs (same as on XJ550 models) that are off a Suzuki, and while some minor differences exist ( i.e the choke plunger system and the locknuts on the synch screws), 99% of the information (and pictures) will crossover to the XJ550 model carbs. MIKUNI CARB REBUILDING INFORMATION GUIDES: Note that an OEM" part may be made by Yamaha's original supplier, even though such part is no longer serviced through the Yamaha factory parts system. NOTE: "OEM" refers to an original Yamaha factory part, whereas "Replacement" or "Aftermarket" refers to a part not made by Yamaha or one of their original suppliers. This ink stamp could have been on the carb bodies, or on the sides or bottom of the bowls.and, after 20+ years and a number of carb cleaning efforts, are probably long gone.ĭifferent series of Mikuni carbs are quite difficult to properly identify from one another, and Mikuni carbs were also used on other manufacturer model bikes, and while even the same "series" of Mikuni carbs may have been used on, say, a certain Kawasaki model bike, the internal jetting, valving, and other design elements (choke actuation method, etc.) typically renders such carbs as "similar but different enough" to not be directly (or even indirectly!) interchangeable with the proper Yamaha version carbs for a particular model. Original carb bodies are typically marked with an ink stamping that identifies the intended use of the carbs.for example, the 1983 XJ900RK carbs (US models) would have an ink stamping that reads "35H00", while the XJ700XNC carbs would be inked as "1FL00", etc. Thus the BS28 series carbs have a 28mm ID throat, and the BS33 series carbs have a 33mm ID throat, etc. The "series" number of the carbs refers to the internal diameter of the carb throat (the area where the butterfly valves are) and is expressed in the closest millimeter measurement. All other XJ models from this era (XJ650 non-Turbo models, XJ700 non-"X" models, and all XJ750 non-X models) used Hitachi carbs. NOTE: Mikuni carbs were originally used on all Yamaha XJ550 models (BS28 series carbs), all 1992-98 XJ600 Seca II models (BDS26 series in the USA, and BDST28 series in the rest-of-the-world), all 1984-85 FJ600 models (BS32 series carbs), all XJ650 Turbo models (BS30 series carbs), all XJ700-X and XJ750-X models (BS33 series carbs), XJ900RK and RL model (BS35 series carbs), all XJ900 N/FN and F models (BS36 series carbs), and all XJ1100 and XS1100 models (both used BS34 series carbs, but there are vast differences between the XJ1100 and many of the XS1100 model carbs). XJ PARTS CATALOG, SECTION C: FUEL SYSTEM ITEMS: Mikuni Parts Ītlanta, GA - Catalog - How-To's - ForumįUEL SYSTEM ITEMS: Including Airbox, Carbs, Intakes, Fuel Tanks, Sending Units, Petcocks, Gas Caps, Tank Mounts, Etc.
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