you need three things for an engine to run. proper air/fuel mixture, compression and spark at the proper time.
If you have the three things that you need Fuel, air, and spark then timing must be the culprit
If getting fuel and spark, then need compression and air.
A 2003 Chevy Suburban will crank but not start if it has no spark or fuel. Checking for a clogged fuel filter or fouled spark plugs can help to resolve the problem.
Does it have fuel, spark, compression?
Could be broken timing belt. Do the spark plugs have spark?
You are missing fuel or spark.
if it is cranking but wont start check for spark, fuel, air and compression.
i would check the timing. check for compression.
Compression ok?
Check to see if engine has fuel at carburetor and if it's getting spark at the spark plugs. If both fuel and spark are good then the problem could be with the timing settings or timing belt/chain is worn out/broken.
For an engine to start it needs spark to the plugs and fuel. Without both it will not start.
compression? bad/worn/broken timing chain..