usually a sign of a lean pilot/idle jet is when you cold start it you'll have to pull the choke & leave it open for a few minutes to warm up the motor or otherwise it just sputters & dies, a rich pilot/idle jet usually is easy to start even without pulling the choke but it blubbers once you crack the throttle & you really have to warm it up before the blubbering clears out, also it won't idle with a too rich pilot jet. a right pilot jet has a very crisp part throttle response you'll know if you have got a right size pilot jet, i always strive for a good clean part-throttle response it helps with getting great takeoffs b'coz you won't be bogging down or blubbering out of the start line.