as i mentioned it has an INTERMEDIATE orifice. Someone more knowledgeable about this type can chime in, but again i'd think the intermediate combines/kicks in around 1500-1800rpm or higher with the idle, then the high speed takes over completely
if you are going to the trouble, i usually never just give it a hone but yea its very cheap if you can get another couple hundred hours out of it and dont mind it being down on power. a new 4 stroke wont last nearly as long as a rebuilt 2 stroke IMO, but they are sweet motors at 5x the cost.
you are describing WOT timing or did i read this incorrectly?? idle timing is around 4 ATDC so you are way too high or the flywheel key sheared. if it did, you will need a new key and lap the tapers or it will slip again.
i think carbs has an intermediate and idle orifice that works around the speed you are describing. be sure to remove the screw to both and be sure they arent swapped in the wrong hole. should be #37 in front (idle) and #44 on top stbd side (intermediate).
costs me , including shipping to Jay's Block shop, both bored, surfaced and washed about $275 for a 2 cyl. bearings sound like they are just fine. can find NOS piston and ring kits on ebay for $50 a pop. thats $375 plus the powerhead gasket kit so $500. Might want 2 new coils and a NOS pack so...