The wiped out engine I pictured spun over fine too....It just wouldn't start...…….
As far as the oil...Is the oil formulated for 2 stroke engine use like yamalube 2-S Pre-mix and not for 4 stroke engines or2 stroke engines with oil injection units..;-Right?...Post up a pic of the oil you're using...….
I have 4 cylinder Yamaha motorcycles and use Yamalube semi-synthetic oil in them too but its 10w/40 and for wetclutch crankcases which is entirely the wrong oil to mix with fuel and run through a 2 stroke engine......
You'd get way better results mixing transmission fluid and fuel together...I know it would because I run it with my backpack blower and have been for over 14 years...Its a 2004 model broken-in on regular 2 stroke at 32:1 but always run on 50:1 Dexron/MerconIII Synthetic transmission fluid after that with 93 octane fuel and its still kicking strong with zero engine/carb problems...
The weedeater I have is slightly younger 2007 model but runs on same transmission fluid/93 octane fuel mix as the backpack blower with zero problems too….
It appears in my years of doing it I can now come to the solid conclusion that mixing trans fluid with fuel kills the harsh effects ethanol has on a carb aswell as engine internals has no ill effects and also seems to elongate the engines life by quite a stretch..Its also a detergent aswell as a lubricant so that definitely helps and is a pretty big factor....LOL
The theory behind your reason about not wanting to strip the sparkplug hole threads when properly torqueing down the sparkplug crushwasher mainly occurs when youre removing a hot sparkplug from a hot engine also installing a cold plug into a hot engine...Rule says you must remove & install sparkplugs in an aluminum head when both are cool to the touch which is room temperature...…..
You'll possibly get whats better known as "Galling of the Threads" when you fail to adhere to the rule and also to mention its pretty easy to feel when a crush washer is fully seated and properly crushed...Especially with a torque wrench..
You'll be surprised how much air gets sucked in and also how much compression you lose having that sparkplug as loose as you had it also surprised to know that the pressure that escapes erodes the sparkplug hole threads.....?
If I remember right It takes almost 2 full turns to fully and properly crush a sealing washer on a brand new sparkplug from the time it starts to get snug with the cylinder...……
Ask any technician who works at a sparkplug company about the ill effects of leaving a 2 stroke sparkplug loose by almost a turn and a half then tell them it was also ran wide open and then send them a pic of the plug....I guarantee they'll say things that aren't good.....
Using a lil anti-seize on the sparkplug threads also helps a lot in successfully torqueing and removing them and also to mention a racers trick to extending the life of the plughole threads too...
You mentioned sportbikes and racing..I did a lil of that myself as a weekend warrior on bikes that also got ridden on the street.......Do you have a compression tester?
One thing about engines no matter 2 stroke 3 stroke 4 stroke 5 stroke or 6 stroke they all need compression to run and should be part of a racers toolbox along with a leakdown tester......…….
You've never owned or operated lawn equipment like a 2 stroke weedeater ,chainsaw, concrete saw or backpack blower ever in your life?..
Its the same principal and useage also FYI back in the 70's and early 80's they had floater carbs on them especially the Homelite models..You couldn't flip them around like the pumper carb models without getting bathed in fuel and flooding the engine.....
By the description of the things you mentioned happening during the ride Id pull the pipe and look up the cylinder because that's kinda the same similar story I got from the old owner of the pocketbike with the wiped out engine I posted a picture of when I bought it...…
I think it would suck to wait for the coil then install it then pull your brains out trying to get it to fire up just to find out the piston started melting down and you didn't have enough compression...Its literally two screws to remove and pull the pipe to the side....Its even quicker to do a compression test.
The old sparkplug was most likely insulated well with burnt oil and ash also to mention Chinese made Torch brand..When that happens to a plug it lessens the intensity of the spark which hinders engine performance and heat build-up...Main part is that it was most likely seated tightly like it should of been with crush washer properly crushed.....
Post a pic of the old plug if ya can....don't clean it either...…...
One thing you have to remember and never never forget is these are Chinese gimmicks kinda like the goldfish in a bowl at the carnival that dies in a day or two if you don't properly care for it....LOL..
They were $169.00 through a pocketbike store and $237.00 shipped to your door brand new in the box under the ruse they are actual purpose built racing bikes …
If you bought every part of one of those cheapie bikes and built one from the ground up it would cost you almost 3 times more money than buying one whole…..Back then it was cheaper to just buy another....LOL
Back then they even sold what was called a stronger beefier framed and more powerful cags for $300-350.00....I had a couple of those models too and they were better built aswell as slightly faster...…....
With the trials and tribulations you have going on with your bike right now would you get much racing in with it as it currently has been running?
It takes a pretty good chunk of money and time to do modifications to make a cag a viable racebike that by the time you're done you could've bought an entry level aircooled/watercooled euro knockoff for $500/650 and had a lot more power and extra power potential despite similar wrenchtime to iron out the bugs.....Those bikes are modeled more for racing...…..
The engines on the pocketbike you have comes from industrial based tools and were never designed for minibikes....The engines are a ripoff of Robin brand tool engines evenwhich a reputable pocketbike company like Blata also did years before the Chinese ever did with the Blata 2.5 which was $1000.00 brand new and I know because I bought one brand new in 1999 and found out that in 2004 that Blata used Robin NB-411 brushcutter engines in their pocketbikes that were designated entry level racing pocketbikes with 3.5hp….
Heres a picture below of the exact engine mounted in your pocketbike frame...Its a 40.2cc brushcutter engine made by TM or SanRen..They also use them for trashpumps and power winches.….
When you look at the engine posted above as it is as a tool engine it gives the answer as to why the sparkplug boot is so odd looking....Reason is because they remove the cooling shroud too which reduces effective cooling.. Some cags were actually sold with it and lots of members removed them....LOL
Just realize these small engines heat up quite well when being worked as plain old industrial tools....Now think about the extra heat stress the engine has to go through with the extra load of a weighted rider most likely at temps in the heatrange you mentioned the other day...[103*]
I dont take my aircooled bikes or nitro r/c vehicles out when temps exceed 90*.....Not even my Harley or my oldschool Yamaha motorcycles....You could literally smell the humidity sizzle off the engines like steam from a hot clothes iron after taking a nice healthy run.LOL
Heavily modded 1989 Honda CBR600 with engine built to AMA racebike specs , 2012 BMW S1000RR , 2005 R6 ,2012 GSXR 750 , 1985 Suzuki GS550E....That's just a few of the sportbikes Ive owned over the years....LOL