i was there when trying to get it running so ill answer your questions with what i know, i was only there one night so i did what the time allowed.
did not spray anything to check crank seals.
2.carbs were removed and carb boots were in great shape.
all cylinders are getting good spark.
all slides are in sync, i do know how to check.
all jets were cleaned and are the same size.
all needles are on the same clips.
all fuel lines are new and fuel pump was cleaned and pushes good fuel to each carb. and compression was tested an all cylinder and all read at 130psi
with what i found i would be leaning towards reeds, the sled has very little for miles, but was stored for a while before we tried to get it running, problematic reed dosnt sound too far out there