Looking at your pic of the piston. that is not pc's of old spark plug. That is ether chunks of old valves or something from the bottom of the engine. What do the valves look like? Did you ever check out the bottom end of the engine? Until you do that you are just fighting a loosing battle.

 

Didn't check bottom of motor. When I had the top end off, I turned the crank by hand and it was free and smooth. How would parts from the lower end make it to the piston anyway? This is a two stroke, so no valves I know of.

 

The starter is bad. There is no reason the motor shouldn't turn over with the plug in.
Now, the heat and quit thing might be another issue.
I guess we need to fix the starter and go from there.


I was hoping that you were closer to me.

 

Valves in a 2 stroke.....LOL
We are thinking along the same lines as far as the reason for the damage should have been found before assembling.

I was wondering about the lower rod bearing but he says it spins freely and I think he should notice if a rod bearing was bad. Emphasis on "should"..LOL

Agent: did you move the rod up/down and side to side to check for play?
"How would parts from the lower end make it to the piston anyway?" They simply blow up into the cylinder thru the transfer ports.

 

I did a little bit. I'm not going to say that it was perfect, as NOTHING on this quad is in good condition, hell, even the front plastics were mounted by drilling DIRECTLY INTO THE GAS TANK.

But, they didn't feel that bad. I mostly don't understand why the quad dies out. It didn't die out until the old piston/cylinder blew. Still idled fine, right up until the last couple minutes when it wanted to die out.

Truth be told is this:
I'm pretty mechanically inclined. I don't know much about 2 strokes, but I can learn. I just in my mind know that I'm going to spend at least $300/$400 bucks getting this stupid thing into decent condition. Fixing fuel tank, figuring out why the rear end is bent (god forbit I break the motor in the process of bending the axle), getting everything else straightened, etc. Oh, and the starter had blown the relay, so that's another $30, or still $30 to replace it with a different relay and the applicable pigtail...

Just really frustrating, I know I made a mistake getting it, and if I keep trying to fix everything, when am I going to finish? Am I going to be spending the next two months of PRIME riding time with my son trying to get this crap fixed? Just hard to decide what to do.

I found a 2011 Kymco Mongoose 90 on craigslist not far from me for $850. Title and all. I've already put $200 plus the $500 I bought the KFX80 for into it, and have a large paperweight to show for it. Could be worth selling something cheap to a friend to get cash to just go buy something that runs, and part out this pile of junk I have now rather than keep soaking money into something, hoping it runs, and missing out on what I really wanted all along. Something fun to go do with my son.

 

ya im not a 2 stroke guy never had one apart..hehe
its pretty easy for things to make it up from the bottom of the engine to the top. If you look at the pc's on the top of the piston the one has some casting marks in it by the look of it that closely look like the connecting pin marks. as far as hard starting their could be a bearing out in the bottom end that is binding when trying to start with plug in but with plug out it does not have enough pressure on it to bind. same theory goes for when it stalls parts heating up and binding. i had a old sled that had the same issue except it was pull start. eventually i found out the issue that the connecting pin had broke but for some reason every time it shut off things would usually line back up to get it started again eventually. even the shop did not figure out the problem since they never tore the bottom of the engine apart like asked. i found out the hard way 4km out on a lake with it all let go. had parts of the connecting rod ontop of the piston. left the machine out their with a note on it free.