Good?Bad?Lean?Just right?Need bigger Jet?

[4izzy]

Spark plug reading?what does this reading mean?jet number #75 just installed? Plug and jet just installed took it for a ride down the road gave it some small revs riding Low and mid good,Smooth but at top end it acts little weird..ima say like poping but not really loud its from exhaust,Like she want to go but it's getting held back..Runtong Carb,upstate Ny 505 elavation..and baffle is removed...B7HS SparkE..gaped at 25