This ones got me stumped

[clearlyblinded]

So I got a 80cc 2 stroke china girl, put her together without trouble and fired her up right away. Ran it rich a couple tanks (i'm now at 32-1) and everything was going alright. Of course the gaskets were garbage (and hardware, plug etc.) so I ordered new parts and was noticing the engine running rough. Would sputter and die at idle so when I got the parts I found my piston rings were shattered. No big deal, got new hardware, plug, gaskets, rings and she was running better than ever.

One day coming home the engine sounded... off. Not sure how to describe it, so I pulled the clutch and hit kill and it stopped immediately. Tried the pedal and no give so I took it right home thinking I seized it up going to fast. As I took her apart no damage to the head, piston, housing or anything I could see. She just won't start now. I've tested the electrical (magneto and CDI register fine and she sparks). I'm getting fuel to the carb, float seems fine and i've cleaned what I can and still nothing. Watched videos and i'm really trying here but i'm not sure where to go next.

Any help would be greatly appreciated. I pedal and drop the clutch and it won't fire. Choke up, down, pulled the kill switch and all that. Hoping for some real wisdom here.

 

[Frankenstein]

OK, well what type of head do you have? I've also had intakes develop leaks on the welds, exhausts can do it too... Is your exhaust port clogged?

I ask about the head because sometimes they just get f***ed up for no real reason, just warp and that's it. If you are using a stock head it may have warped suddenly and that will make things worse.

Blowing a crank gasket (under the small gear on one side, and under the magnet on the other) can make for some bad running, notice any liquid oil/gas under either the clutch gear cover or magneto side cover?

You have spark, you're obviously receiving gas if it's in the carb and its all clean, that leaves air as the last contender, if the leak is bad enough then the choke may never be enough to start it, but often if it's a bad leak you can still get it to run with starting fluid and the choke off since it's easier to get that stuff burning to get the ball rolling than straight premix.

You can even put some right down into the spark plug hole itself and try starting, then see if you can determine a leak point once it's actually going. May even be a stretch but an oversized jet can sometimes help by letting the bike start and still have a good air/fuel ratio, I have a size 100 for stubborn motors or super cold days, it was drilled with a 1mm drill bit, doesn't get used often at all but in the small handful of times it did get used it worked fine.

 

[clearlyblinded]

Frankenstein, glad you answered as I've read a lot of your posts and you know your s**t. So I did take the stock head off and the housing for the Piston (surprisingly I can't see and damage or warping) and I have not seen the leaking you speak of. I had to pick up some starting fluid so I can try that next.

While I have your attention, the kit I got was cheap and it's coming back to bite me. I'm looking for a better motor, had my eye on the dirty rat or flying monkey from bicycle motor works but I'm curious what you would be looking for. Thanks for your response.

 

[Frankenstein]

I will have to go with the masses, pick up an iridium spark plug if you haven't already, for whatever magical reason they solve half the problems...

Did you notice oil or gas like stuff in either the clutch gear (large) cover or the magneto cover? If you don't have good gaskets on those covers you might not get a build up of liquid, but you may notice a lot of oil build up under one side of the engine.

By sounding off... What do you mean? Like kinda sluggish? Did you try starting the bike without an air filter for a moment? Some filters just get clogged with oil so bad they can't breathe at all...

What type of carburetor are you using again?

You said you took the cylinder off for some reason or other... Did you replace the base gasket if it torn? Did you check if it was damaged before reusing it?

The stock head gasket you received was silver right? If so and you reused it maybe? I don't think you would you ordered new ones...


Is your magnet on with the keyway at 1 o'clock with the piston at top dead center?

That might be the only thing left that could be the problem...

Sometimes they just start slipping out for no reason, bad timing or at least slightly off timing would make kinda off riding..

You said the piston rings shattered and you see no damage? What do you see exactly? Just curious..