Yamaha Jin Hu 150 motorcycle magneto has a 1 and a horizontal I, which is it when adjusting the valve?

That's the horizontal T point, not 1, so the observation hole is too small, and there is dirt on the flywheel, which is difficult to see clearly. You can adjust the valve without looking at punctuation marks. Just remove the spark plug and put it in the cylinder with a Torx screwdriver. Turn the magneto with a tool, and feel whether the piston rises to the highest top dead center with the hand holding the screwdriver. Another method is to directly remove the two valve covers and turn the magneto with a tool, and the valve will work. When the intake valve is pressed, the exhaust valve is closed. You can start adjusting the exhaust. When adjusting the exhaust, turn the magneto to the exhaust pressure, open the air intake and close it before adjusting the air intake. Tighten the air intake, but don't force the valve to leak. The exhaust can be looser, leaving a small gap. Too tight will affect the power output. It's boring, just understand and explore slowly.