The fuel system consists of the fuel tank, two shutoff valves with fuel filters, three Mikuni constant velocity carburetors, and an air cleaner.
The exhaust system consists of three exhaust pipes, a crossover pipe, and two mufflers.
This chapter includes service procedures for all parts of the fuel and exhaust system.
The air cleaner must be cleaned every 1,000 miles or more frequently in dusty areas.
Service the air cleaner element as described under Air Cleaner in Chapter Three.
CARBURETORS | BASIC PRINCIPLES
An understanding of the function of each of the carburetor components and their relationship to one another is a valuable aid for pinpointing a source of carburetor trouble.
The carburetor's purpose is to supply and atomize fuel and mix it in correct proportions with air that is drawn in through the air intake.
At the primary throttle opening - at idle - a small amount of fuel is siphoned through the pilot jet by the incoming air.
As the throttle is opened further, the air stream begins to siphon fuel through the main jet and needle jet.
The tapered needle increases the effective flow capacity of the needle jet, as it is lifted with the air slide, in that it occupies decreasingly less of the area of the jet.
In addition, the amount of cutaway in the leading edge of the throttle slide aids in controlling the fuel/air mixture during partial throttle openings.
At full throttle, the carburetor venturi is fully open and the needle is lifted far enough to permit the main jet to flow at full capacity.
Subject: 1977, 1978, 1979, 1980, 1981 Yamaha XS750, XS850 service, maintenance, repair. ISBN-10: 0892872438 | ISBN-13: 9780892872435 | Clymer M404