Venom Vader 125cc tach not working

[additivewalnut]

All in the title, bought the bike with the big bore kit motor off the frame. Put it on, runs decent, I think it needs a new carb or something bc it feels like it doesn't really have any power and I can't seem to get it to go over 30mph, but I can't tell at what RPM range power falls off. The tach just 100% doesn't work. Nothing shows up on the screen to indicate that it's at 0 rpm or anything, just blank.

Is there a sensor or wire I'm missing or do these just not have functional tachs?

[TominMO]

As to the power situation, check both the valve timing and valve clearances. Simple and free. Then look into carb issues. Maybe it's too small, needs rejetting, or the motor needs a better carb.

By valve timing I mean that the marks line up on the sprocket in the head. Just being off one tooth can matter. Never assume someone before you did their job right.