ATVConnection.com ATV Enthusiast Community - Coolster 125 Chinese quad basic ?'s

Hey y'all nice to meet you first post here my name is Mike Berry I just had a few questions about a Chinese quad called a coolster 125 CC ATV.
I'm using a cell phone and voice to text so please don't jump my ass for poor grammar or punctuation.

long story short I was doing some volunteer work at the local landfill and somebody came up there with a coolster 125 ATV Chinese quad that was in very good shape but they said they couldn't get it to start so they quit playing with it and we're going to just throw it away so they dropped it off at my house since I helped them unload about 3 tons of trash and the ATV has the following problems,
does not start or idle readily and it does not respond to throttle response easily the start switch button does not activate the starter although the solenoid is good it was full of stale water down crappy gas and it had a severe toe in problem which I fixed by using a couple of wrenches and turning the turnbuckle to straighten out the wheels the best that I could.

anyway since that I got this ATV it's going to be for my eight year old kind of stepson my girlfriend's son and it is quite powerful when I can get it to run but it does not I have clean the carburetor but the carburetor just seems to still have some issues when I adjust the carburetor which is a pz20 it wants to either bog or straw when you give it throttle response or when you adjust air fuel idle mixture it doesn't want to idle high enough for it to go into gear.
so with that being said I ordered a new carburetor also I melted the starter by trying to get it to start and keep it tuned so I ordered a new starter and I am going to straight wire a hot wire to the solenoid since the push button start does not work and bypass All That Jazz.

but I have a several few questions such as on these 125CC what I believe to be Honda clones what size plug does it use I've had a very hard time finding one that have the small enough thread pattern and the removable tip for the spark plug boot to go on to also is there a carburetor available other than the stock style carburetors that has idle speed adjustments that does not mess with air fuel injection mess mixture?

also I I understand that it has a wet clutch and it needs an oil change probably in both crankcase and gearbox oil reservoirs so I bought some high-quality oil of the correct specification but I do not know which plug is which gearbox or crankcase I can't find a proper online manual that's not in Chinese and I need to know how much oil it takes and which crankcase or gearbox and how to check the level I found the dipstick for the regular oil for the crankcase but I'm not sure how she know how much oil to put in for the gearbox.

when I start the bike by jumping the solenoid because the start switch does not start solenoid I can get it to idle and I can get it to run while it's in neutral but the second I put it in gear it dies however if I start it in gear I can ride it for a few seconds before it dies and as an ASC Certified mechanic I do know how to diagnose lean and Rich fuel conditions but it doesn't seem to be that issue it only wants to run on about 3/4 choke but the spark plugs so messed up from being so old I can't find the right spark plug which is supposed to be a c7hsa but every time I go to the auto parts store they give me a non-compatible completely different size spark plug although a c7hsa is a very popular plug dummy at the register can't figure that out so where can I get the proper spark plug of extremely high quality?
as far as gas I drained out and wash the original tank out replace the fuel filter and use high octane ethanol free gasoline which made a big difference in the quality of which the motor run but still doesn't stop the sputtering bogging and stalling out when you're trying to go under acceleration.

also the master cylinder for the rear brake the brake line and the rear caliper were both well all three I might say screwed up so I found them online on Amazon for $20 for the entire set and I ordered it and should be here in a couple of days at least then I can wrap it up without it trying to run my legs over while I jump it off with screwdriver and by the way when those little ATVs run over your legs it hurts like hell!

so any suggestions on how to trace down whether or not the start switch this evening receiving or putting out power would be gratefully accepted along with where and how much oil goes where on this little motor and gearbox pictures would be appreciated and where or what spark plug I can get locally would be a good replacement and I'm not necessarily partial to NGK or Champion or any other major brands I could care less I just want one that are good spark and longevity also I would like to know if there's anything I can do to a factory replacement carburetor who are the original or if I should just order a high-dollar aftermarket if it's worth it to be able to adjust it to run properly without sputtering bogging or some other stupid throttle response issue or idle issue.

I'm sorry for the long post this is my first post and new member here as of today but I appreciate any responses and or pictures information or there for anything useful to getting this thing running for an 8 year old boy although I do know how to govern it which will be done because when I did get the ride this thing it was way too quick way to fast for somebody with no experience.
anyhow thank you very much I'll be awaiting responses hope you all have a great night morning day or whatever time it is when you see this

Mike Berry