Adjusting the valve on a Suzuki GS motorcycle is a two-step process that involves checking the amount of space -- or clearance -- between the valve tappets and the camshafts that operate them. Once the clearance between the camshaft's lobes and the tappets are determined, adjustments are made by replacing a metal shim that sits on top of the tappet with a shim of a different thickness. Some parts of the motorcycle will need to be disassembled for this task.
Lift the motorcycle onto its centre stand. Remove its fairings, if equipped, using a four-mm Allen wrench. Unlock and remove the motorcycle's seat, using the ignition key. Unscrew the mounting bolt at the gas tank's base, near the seat's rails, using a 10-mm socket and wrench. Turn the gas tank's valve to the "On" position, and pull the fuel lines away from the valve. Lift the gas tank off of the motorcycle's frame.
Unscrew the bolts from the round crankcase cover on the right side of the motor with a Phillips screwdriver or a four-mm Allen wrench. Pull the cover away to access the motor's crankshaft. Place a 19-mm wrench over the nut at the end of the crankshaft.
Unscrew the tachometer cable from the motor's cylinder head cover, if present, using a pair of rubber-jawed pliers. Unscrew the cylinder head's bolts with a 10-mm socket. Lift the cylinder head cover off of the motor to access the valves' tappets and camshafts. The GS motors are equipped with two camshafts; the camshaft at the rear of the cylinder head controls the intake valves; the forward camshaft controls the exhaust valves.
Rotate the crankshaft counterclockwise with a wrench to turn the camshafts. Stop when the exhaust camshaft's round-tipped cams on the right side of the motor are pointed at a 90-degree angle away from the top of the cylinder head. Measure the clearance between right exhaust cams and their tappets with a feeler gauge. Suzuki specifies a clearance range of 0.001 to 0.003 of an inch of clearance between the cam and the top of the tappet.
Adjust the exhaust valve's clearance by replacing the existing shim with a new shim that is slightly larger or smaller than the original shim, according to the measurements taken in the previous step. Push the exhaust valve's tappet away from the cam, then pull the shim off of the valve with forceps. Coat the top and bottom of the new shim with 10W40 motor oil, then slide the shim into place over the tappet. Skip this step if the clearance of the first two exhaust valves are within 0.001 to 0.003 of an inch.
Rotate the crankshaft 180-degrees counterclockwise with a wrench so that the intake camshaft's cams are away from the intake valve's shims on the right side of the motor. Measure the valves' clearance with a feeler gauge and replace the shims as needed.
Rotate the crankshaft 180-degrees counterclockwise with a wrench so that the exhaust camshaft's cams are away from the exhaust valve's shims on the left side of the motor. Measure the valves' clearance with a feeler gauge, and replace the shims as needed. Repeat this step to check and adjust the remaining intake valves' clearance.
Reinstall the cylinder head cover onto the motor, and tighten its bolts with a 10-mm socket. Reinstall the right crankcase cover and tighten its bolts with a four-mm Allen wrench. Screw the tachometer cable into the cylinder head cover and tighten it by hand. Reinstall the gas tank onto the motorcycle and reconnect the fuel line to the carburettor. Reattach the seat and reinstall any fairings removed earlier. Use a four-mm Allen wrench to tighten the fairing's bolts.
Older models have a hinged seat that should be removed for greater access to the motor. Pull the pins out of the seat's hinges, then pull the seat off of the hinges and away from the motorcycle.