Athena 70cc Big Bore Cylinder Kit - 47.66mm Bolt-On Performance Upgrade for Dirt Bikes & ATVs | Off-Road Racing & Trail Riding Enhancement

I purchased this kit for my 2005 Zuma 50 after the previous owner managed to melt the piston rings on the original motor in 1080 miles. Installation took a very reasonable amount of time, and because it's a 2-stroke, there's not much that one can mess up. The instructions are a bit dense for someone with no mechanical skill, but a quick search online of forums or YouTube makes installation a breeze.A couple notes: When you install the new top end, torque everything to spec, take a short ride, and check it. Also, break in with rides, not idling on the stand (remember its air cooled), making sure to vary the throttle. After a tank or two, you should be good to go! I've put 600 miles on mine since doing the swap a month ago, and it runs as well as stock Zumas.For reference, I have a 17.5mm Dellorto Carb with autochoke (running needle positions/jetting exactly as I pulled it out of the box from Team Calamari), a Leo Vince ZX exhaust, and the rollers/springs that were included with the ZX exhaust. I've gotten a GPS confirmed 50 MPH out of it with great acceleration, holding 35 MPH up some of the steeper hills in the Seattle area. I highly recommend this kit, but make sure that you retune your carb (or invest in a larger one) to prevent a lean condition that could cause premature wear.**Update** I've put over 1500 miles on this cylinder kit (longer than the original Yamaha) with zero issues. There has been no drop in performance over this time. I'm very impressed at the longevity and durability of this single-ringed cylinder.