1987 E40ELCUD Power Pack failed again

I replace the power pack on my 1987 Evinrude E40ELCUD motor. (It wouldn't start). After replacing it, it started fine. I took it out on the water, and ran it, but I didn't run it fast. (I had an emergency, so I had to quit, and get home). The next time I took it out, it went about 300 yards and stopped. I was going under 10 mph when it stopped. I had a mechanic check it out. He removed the fly wheel to make sure nothing was broken, and that it was 'in time.' You see even though I didn't feel it, my prop had two chunks out of it that appeared to have been caused by a submerged fence post. Everything under the fly wheel looks fine. I am getting no spark across the spark plugs. The mechanic said it appears that the power pack went out again. Does anyone have any suggestions as to what may be causing the power pack to fail?

What's your dva reading ?

So cavitation might be problem

I haven't checked. How do I check the dva reading?

I did raise the motor, so cavitation could be the problem. I did make sure the water pump was working, and I did operate the motor at a low speed. I raised the motor since I was going fishing on a shallow lake with many stumps. Do you think this could be the problem?