Lapping in valves

It is easy to lap valves, I lap them to check my valve jobs. It is pretty time consuming to seal the valves that way. To get the suction cups to work, you should clean the valves up, both sides of the head. I use a wire wheel on the valve head and stem in the valve bowl. I try to minimize contact with the stem that contacts the guide. Lapping just a little bit will give you a good Idea of where the valve is not sealing. Typically the exhaust valves stem and guide will be worn out of tolerance with the intake stem and guide being pretty good. Water based compound is fine for lapping.