Hi Doug
When you go to start it, do you prime it, push the lever down to run, and then back to start?
Doing this makes sure the kill wires aren't connected. With one of mine, it 100% refuses until this is done - after 10 pulls, it will go - possibly the vibration from pulling the cord eventually jitters them apart.
Also, if slow speed is a fair way down the throttle range , perhaps the cable is maladjusted, and putting it on start still has the stop wires earthed
Regards
Tyler
