won't start

76 Onan 16 hp case tractor,replaced starter and points,what can I do

A little more history would help. 
Has the machine been running recently? 
Has it sat for awhile?
How old is the fuel?
Does it have a fuel pump?
If you spray carb cleaner down the throttle bore, (while cranking, will it kick off momentarily?
 
Going to have to investigate and narrow things down..
 
 
Do you have spark at the spark plugs? (pull the plugs out of the head ground to head while plugged in and crank over.  
 
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