You need spark, compression, and a combustible fuel mixture to run your engine.
Assume you have the first two; you can ASSURE you have the third by using STARTING FLUID. Remove right side panel, remove air cleaner; squirt starting fluid into area of carb intake . . . then crank her up.
If it runs 'til the starting fluid is gone, then you've a carb or fuel supply problem.
Use the starting fluid judiciously; have a fire extinguisher standing by, and "Don't try this at home."
Opinion only, and a minority one at that, probably, but--the hazard of too-tight valves (provided they close fully) is burned valves, I think, rather than starting problems. If the valves close sufficiently to develop compression, engine oughta start, seems to me, but I certainly could be in error.