I replaced the 50 in my YSR with a lifan 150 upright engine.  It's a brand new engine.  It won't start.  I am getting spark, and the carb has fuel.  It pops, but won't run.  I have a feeling the timing is off, as I am getting a flame out of the exhaust.  I have done the typical adjusting of the valves that everyone recomends, but it still won't run.  Compression seems good, and I am getting tons of spark. 

How do I adjust the timing on an upright 150 (like an xr150 engine).