The manifolds in my 1998 305 Mercruiser were leaking badly, (went thru 2 starters form compressing water). After sitting for 3, 4 months I finally had time to tackle the problem, too late engine was frozen, replaced manifolds, added fresh water cooling system, and rebuilt heads with new valves. Put it together and can't get it to start. Had problems adjusting valves, book said after lash 360 degree turn, but too tight, and no compression had to loosen to bring compression up. I have compression of 100 psi, good spark and fresh gas. Any suggestions