Does sound like it could be poor ignition from a weak spark, and its easy enough to check the plugs so start there. If they need replaced, whack a set on, if there is still no joy check for a spark when you turn the engine over, holding a plug against the head (make sure your insulated), two people needed for this obviously. Then check if its getting fuel- take a sniff at the exhaust after trying to start it, and/or check if the plugs are damp with fuel... you'll soon start ruling out either the ignition or fuelling side of things. good luck