Hello,
I have what I believe is a 90cc Coolster, the piston was seized and very scored. I completely tore down the engine and cleaned everything up and put new seals in. There were a couple of things during reassembly that i questioned the location of but think I figured them out. After putting it all back together a new starter really struggled to turn the engine over. I checked timing multiple times and backed the valves way off but it still could not do it. I took the head, flywheel and starter chain sprocket back off and the engine moves very easily and smoothly by hand. When I put the starter chain sprocket back on the crankshaft it does not move smoothly, there is a drag. I notice what looks like a bushing in the sprocket bore that I can't get to move, should this be free to spin? I am wondering if this bushing is causing the drag or if I am missing a washer or something and the sprocket is dragging on the back cover plate. Or could the seal be incorrect and is too snug making it hard to spin?

 

Ok, so I feel a little silly, I was chasing something that probably was not really an issue. I was using small gauge jumper wires
to the battery and after reading another post on here once I hooked directly to the battery it really zings if over now. Now to figure out why I don't have spark with completely new wiring, stator etc.