Engine performance problems can be alarming and dangerous when driving a motorcycle. Hesitation on acceleration or engine stalling can put the motorcyclist at risk. The lean-drop method of carburetor balance adjustment can correct drivability issues without the use of expensive specialty tools. However, adjustments may not be needed if new or cleaned air filters restore performance to desired levels.
Remove the pilot screw bore plugs by drilling a 5/32-inch hole in each plug. Drive a self-tapping 4mm screw into the hole until the plug turns with the screw. Pull on the screw head with pliers to remove the plug. Repeat this procedure on the remaining carburetors.
The carburetors are numbered the same as the cylinders they service. Begin adjustments on carburetor number one. Turn the pilot screw in while counting the turns needed to lightly seat the screw. Turn the screw out the amount of turns counted and repeat this procedure on the remaining carburetors in numerical order.
Start the Magna and run the engine until operating temperature is attained. Shut the engine off and set the bike on the center stand. Connect the tachometer, as the tachometer mounted on the Magna is not precise enough to measure the slight differences that need to be detected.
Start the engine and adjust the idle speed to 1,000 rpm within a tolerance of 100 rpm up or down. Adjust the idle speed by turning the black plastic knob protruding between and beneath the carburetors. Turn each pilot screw out one half turn and note the engine speed. A minimum engine speed increase of 50 rpm should be attained. Continue turning the pilot screws out in quarter turns until this increase occurs. Turn the screws out a half turn each until a decrease of 50 rpm is achieved. Turn the idle speed adjustment knob to maintain 1,000 rpm afterward.
Turn the pilot screw on the number one carburetor in slowly until a decrease of 50 rpm occurs, then turn the screw out one full turn. Repeat this process on each carburetor in numerical order while maintaining an idle speed of 1,000 rpm after each individual pilot screw adjustment. Disconnect the tachometer and test drive your Magna. The throttle response should be crisp and powerful, with no hesitation or flat spots in the rpm range.
Idle speed changes that occur with handlebar movement indicate a need for throttle cable adjustment. Old gas can also create performance and maintenance issues. Drain the gas tank and carburetors for storage purposes.
These adjustments may conflict with local laws or regulations for your area. Emission test failure may require readjustment or installation of new pilot screw bore plugs.