This is one of the many reasons to keep an exhaust on your bike.

If your cylinder base gasket leaks it will cause a lean condition and can fry the engine. Same for the crank main seals,or the crankcase's split line gasket which has a very thin portion between the crankcase and the through shaft for the rear drive. Stock gaskets for the most part are not very well made the crankcase split line gasket if not disturbed seems to hold up but I know of some riders who have had them leak a sign is oily black poo coming out of the top back of the engine right under the carb or out of the sprocket area or under the other side where the clutch lives.
Sometimes the engine seals will not be seated in far enough and the mag rotor will eat it up or on the gear side, the small gear will eat that seal up. the seals should be flush with the case or just a little below flush something to check when you first get your engine plus you can check and clean these area as there is metal shaving under the covers that can and will wreak your seal areas or worse tear up the mag coil etc.
Norman

no exhaust also runs the engine way lean

I made it smaller, is that good enough?

holy schniekies batman!!

could this happen with the bottom part of a cheap chinamuffler falls off and someone just uses a bent into a sort of u shape to hold the outer tube of the muffler onto the pipe? (with all muffler guts intact, just not having the small hole at the bottom of the standard muffler for exaust gas to go through, rather having pretty much the entire bottom of the muffler wide open, because there's no cap on the bottom with the small pipe for exhaust gas to exit)?

could this happen with a muffler in that condition?

i sure hope not, but the engine's recently lost power twice, and is currently smoking just about all the time even with a 25g:1o mix, and the needle's clip is on the highest position (leanest mix possible, just did that today and rode it around a bit n 6.5 miles home)

could a muffler in the previous mentioned state ruin an engine like this? is a COMPLETE 2stroke bikeengine muffler ALWAYS needed?

if so i wished i'd known this before having started riding the borrowed bicycle, i'll likely end up having to replace the feller's engine, but at least i'll know to never even start my own (recently aquired) engine without a FULL COMPLETE MUFFLER on it.

note: the muffler onthe bike i'm talking about just had the bottom of it fall off (the one that caps the whole bottom n has like mby a 3/8's hole/pipe for the exhaust to go out?) and the owner of the bike decided to use a flat metal piece bent in sort of a U shape to hold the rest of the muffler in place. i've meant to get a new muffler for it b/c the thing's way too frickn loud, but havent had the money, and for 100bux for my own motorbike (my ONLY means of transportation atm, i couldnt turn down my new bike, despite the missing plug wire and plug.

someone pm me plz if the missing part of the muffler could have caused the major loss of power and always smoking of the cruiser's engine as i may not find my way back to this post. (or if gradual loss of power and ending up constantly smoking and major loss of acceleration sounds familiar and you know what it is that caused it)

[i've been through the carb, not dirty or clogged... i've replaced the spark plug, i even removed the exhaust sys to see if it were plugged, and best i could tell (without compressed air) it at least wasnt significantly clogged.. also adjusted the fuel/oil mix to 25 or 26 to 1, from 20to1, and after it having started smoking alot and major loss of power, i also moved the needle down/clip up to try n lean it out, it seems to have helped and the bike'll still cruise at about 20mph, slow cruisin the way i like (b/c of vibration of the engine at 22-30mph)

anyway, before i fill an entire forum page, i'll quit lol... someone pm me if u know whatsup with the friend's engine, i hope its not too bad to fix, but then again its not my fault he "fixed" his muffler with a metal bracket instead of doing the proper fix and getting another muffler

It's possible, but TBH there's so many other things that don't sound quite right to me that I suspect it's a matter of a buncha stuff being a lil off than any one major thing wrong (hopefully lol).

First thing I noticed is ya said the engine "lost power twice" - does that mean it got power back again at some point? If so it's prolly jus' the following;

I'd try and get the thing as close to "normal" settings as possible - carb needle set to 2nd frm the top, good quality 2-stroke oil mixed @ 32:1, NGK B6HS gapped @ .030" & try and repair/replace the endcap (or get an expansion chamber if ya have the pennies).

no, the lost power twice was compared to when i first started riding the bike, it lost some power but still got me around alright and didnt smoke. then the other day while on my way to sarasota it lost power again and started the smoking. currently the needle clip is on the highest position which got rid of some of the smoking and got it running a little better (or it did at the time of the adjustment).

for oil:fuel mix, it was near 20/1, i drained it and adjusted the ratio to 25/1, would these china engines still run alright on 32/1? (get enough lubrication)

and idk about b6hs, but i have a BP6HS i think it is, gapped as close to 30 as i could get by eye (i'm frign broke and dont have the money to even buy a gapper lol, and lost the one i had)

So long as it's a quality oil, 32:1 is pretty much the standard mix - more than that would prolly explain the smoke, as for the plug it seems the "P" one has a slightly extended tip, but if it's not hitting there's no prob: http://motorbicycling.com/f3/ngk-bp6hs-versus-b6hs-differences-17994.html

The gap is pretty important, I'd bug a buddy to borrow a gapper if ya can't get one

What color is the electrode?

i'm not sure about the color of the plug as it hasnt really been in there that long, and i'm not gettin up again tonight lol, heckuva day today that resulted in my 'new' motorbike (a used one), chewing up its own pistion, head, and cylinder, because of (what i think happened) the ring cracked and created the first bit of debris in the cylinder that caused all the other damage. and this happened before i'd even had it running one time, but i guess at least the cruiser got the pipe outta the $150 deal, and i have a full pedal power bike lol (so not worth $150)

but the one i used (ngk plug) isnt hitting the piston, so seems to work for this engine... i just hope them deciding to leave the bottom of the muffler off and me having to ride that to work, didnt ruin the engine.. because that'd make two engineless bikes around here... tomorrow's gona be a rough day too. (pedaling my bike to work so the friend has a means available to transport his arse to find a job)