Ive opened it and they look clean and ok

 

cap looks ok

 

So you've got fuel and spark so the question would seem to turn towards either timing or the quality of the fuel and spark. If the spark is weak or not consistent, I'd think ignition amplifier or coil. If the fuel pressure or volume is low, I'd think fuel filter or pump.

 

Did you make sure someone didn't fill it up with diesel? (just a thought, I've seen it happen more than once)

 

What he said as well as check it for diesel like BK said.
It should still run on diesel but just be hard to start and smoke alot.