yamaha blaster kickstarter feels weird and seems to rev up without giving gas

[Gideon]

hey so ive got a 2006 yamaha blaster special edition and ive never even got to ride yet bought a engine off a ebay seller with a wiseco piston with 4 hours on it. and for a long time she seem to kick over fine but as of lately it feels really wrong sometimes i go to kick her over and it just stops midway or just feels stuck or jammed but it will still go all the way down.and yes ive been in the side of the crankcase and everything seems fine. also sometimes she will start and when she does she revs up extremely high without me giving her any gas. she used to idle fine and turn on first kick before i bought a carburetor kit because she wouldn't stop leaking gas and now she dosent leak at all. the float is adjusted to stock height. ive been through so much with this f*cking quad and any help would be much appreciated

 

[Larry's Shee]

Start by removing exhaust and inspecting piston and cylinder through ex port. Slowly turn engine over so you can tell at what point of stroke piston hangs up. Before you do ANYTHING else, do a leak down test.
Dollar says seller used a Chiwanese cylinder. Another dollar says piston ring is hanging up on exhaust port. Another dollar says an air leak is causing the high revs. That’s what the test will revel. Could be head or cylinder weren’t retorqued after heat cycles. DO NOT ride or start it until fixed. You might be able to fix it before major damage.

 

[Gideon]

Start by removing exhaust and inspecting piston and cylinder through ex port. Slowly turn engine over so you can tell at what point of stroke piston hangs up. Before you do ANYTHING else, do a leak down test.
Dollar says seller used a Chiwanese cylinder. Another dollar says piston ring is hanging up on exhaust port. Another dollar says an air leak is causing the high revs. That’s what the test will revel. Could be head or cylinder weren’t retorqued after heat cycles. DO NOT ride or start it until fixed. You might be able to fix it before major damage.

Ok I will do all of this when I get home Monday, funny thing is when I take the spark plug out she turns over fine and she goes down real smooth and doesn’t get hung up but as soon as I put it back in the problem returns.

 

[Larry's Shee]

What plug are you using? What did it look like when you took it out? With exhaust off look at top of piston for dents/marks