How to Adjust the Valves on a 150Cc Scooter Engineby Tom Lutzenberger; Updated November 07, 2017
Items you will need
Performance intake gasket for a template
Performance cylinder gasket for a template
Black permanent marker
Hand-held motorized grinding tool
Soft metal grinding bit
Large bin for washing
Adjusting the valves or ports on a 150cc scooter involves delicate work grinding away at the existing surfaces to allow more fuel and air to pass. If done wrong, the work can ruin the engine case, creating a weakness where the case walls begin to crack. Shaped incorrectly, the work ends up being a waste of time and provides no improvement in engine performance. Using the steps below, you can minimize the risk. This approach assumes the engine case is stripped and bare before starting the work.
Purchase the performance intake valve gasket and cylinder base gasket you want the 150cc engine ports to match. Place the intake gasket against the intake port so that it covers everything except the original valve areas that must be removed.
Mark the intake surface section not covered by the gasket with a black permanent marker. Thoroughly ink it so that the black ink won't wipe off. Remove the gasket when finished. Complete the same process with the cylinder base gasket against the cylinder part of the engine case.
Place the inked engine case under a bright light. Put yourself in a comfortable position to sit or stand for a extended period of time. Attach a soft metal grinding bit to a hand-held motorized grinding tool. Turn the tool on and carefully begin to grind away the engine case metal to match the markings on your case.
Stop periodically to remove ground material from the engine case ports with a brush. Grind carefully so the finished surface is a smooth adjustment matching the marker pattern. Avoid grinding where the ports or valves begin to transition to flat.
Finish the grinding and wipe away all the removed material. Examine the valves for any areas still needing work. Remove the tool and take the engine to a bin. Wash it with water to remove any remaining bits on the engine case. Dry the case off. Prepare to reassemble the engine with the newly widened valves.
Take your time porting and grinding. Work slowly and shallowly until you become comfortable with how the grinder works. Begin deeper work when comfortable.
Be careful not to grind the ports to thin. They will not have sufficient material to stay complete and will crack when the engine combustion process creates pressure.