Small Engines (Lawn Mowers, etc.): wont start, hiya jason, compression stroke

Question
I was given a brand new briggs 15.5 hp ohv engine.Model 28n707 Type 0173-01.Only thing wrong w/ engine was factory left off one valve seal and one valve cap. They also didnt set valves. I noticed the cap missing and opened crankcase to check if loose valves let it fall inside. It hadnt. I replaced them. Now engine turns freely w/plug out. With plug in it turns over several times and then jumps like its jammed. Then it turns over some more and repeats but never starts up. Could I have put something back wrong inside?I know timing marks are lined up.Only other thing taken out was The plastic gear I guess the governor? Any help would be great.Thank You Jason

Answer
Hiya Jason-
When you say "jumps like its jammed" do you mean it stops like its hitting a valve (sounds like it) or backfires like its jumped timing?

Actually sounds like the timing is 180 deg out.  Find TDC on compression stroke, and check your timing marks on the cam gear.

Lemme know -