How much is the difference in chain tension is there from when the chain is at its loosest point to the point where it’s the tightest? At its loosest, measure the amount the chain travels up and down at a point halfway between the gears. At the same position, measure the chain when it’s at its tightest. Does it go from 40 mm to 5 or does it go from 25 mm to 10?
You indicated that the problem occurs every rotation and a half. Of what, the axle or drive gear? But either way it doesn’t make sense. If the problem was the drive gear, with every rotation of if the chain should tighten. And rotating the drive gear would get you a half turn on the axle. Sorry, but you can only have one bend in the axle. Rotating the axle should get you over seven turns of the drive gear.
Think you’re at a point for some careful measuring. Check the axle for run out and then the gear carrier on the axle. With new gears, check their alignment. I’m guessing you’ll find the drive gear is either toed in or out. The wear pattern on the front sprockets should give you an indication.
LAD Specialties customer / tony kart / rotax / kt100