Hi sparker ,speedy, Norm
I would check the easiest things first , I've had this problem with bad spark plugs ,coil air gap too small ,bad coil ,worn
rings or guides ( if it was guides or rings it would blow smoke on start up) over fueling is a possibility if the carby has a problem
like needle and seat leaking when it should be closed .
Incorrect valve clearance can be a problem especially is someone has adjusted valve clearances at top dead centre.
The light bar blades on mowers haven't given me a problem with kicking back after they have been serviced / repaired.
Cheers
Max.
