Last resort post. I don't know what else to try!

[Camden]

My 80cc 2 stroke engine on my bike will not start. This is my first motor bike, I bought it pre built off a guy on craigslist, and I'm sure this is where my first problem lies, but here we are. It spun like a top all the way home from the store I met the guy at, and some more around the neighborhood and then sputtered out and died.
I have replaced the carburetor, taken the brand new carburetor off and apart and really got in there with a can of cleaner just to make sure.
The carb bowl has fuel in it, float seems to be in working order.
I've also had some local guys over helping, we've tuned the carb albeit it doesn't seem to matter where any of the idle screws or throttle cables are positioned, she tries to start and sputters right out.
I checked for a spark, plug seems to be sparking correctly, but just to be sure I replaced the CDI box and magneto coil, checked again for spark, still seems to be sparking fine.
I then checked for compression, I removed the spark plug, stuck my pinkie finger in the hole, gave it a spin, compression seems textbook.
THEN in a fit of desperation, I drained the gas tank and put brand new fuel in there, again to no avail.
The only difference I've had in sound is since cleaning the carb and changing the fuel, I get a little backfire "pop" after it sputters out.
I tried doing everything I know to do before coming to the forums, but here I am, clueless! Any ideas? Thanks!

 

[Camden]

Magnet weak, grounding, bad fuel filter, bad tank filter. How is the fuel flow to the carb?

I replaced the magnet, so it shouldnt be weak right? there is no inline fuel filter, but theres no gunk in the carb. i haven't checked the tank filter. I was told about a tank filter, but I was having trouble seeing it when I drained the tank. Fuel flow to the carb when the gas valve is on is a small, steady stream.

 

[Camden]

The tank should be able to empty in 2-3 mins, not really a small stream. Unscrew the gasvalve (petcock) from the tank and check the filter.

Alright, I'll check it out. It did empty out in about 3-4 minutes, so maybe my idea of a small stream is different.

 

[mark20]

Alright, I'll check it out. It did empty out in about 3-4 minutes, so maybe my idea of a small stream is different.

did you replace the spark plug? i had the same problem and it ended up that i had a bad plug. most frustrating part is it looks like it has decent spark outside, but doesent acutally spark inside, i almost pulled my hair out trying to figure it out
i replaced it with a NGK b6hs and it runs like a dream!

 

[gary55]

We had a back fire here folks. Was it through the carb? Was it a poof from around the head gasket? Backfire is usually sucking air from somewhere it shouldn't be like a warped head, or timing f***ed up. Could be a scoured cyl. Never seen a fuel filter or a bad plug cause a backfire.

 

[FurryOnTheInside]

I don't think it definitely backfired. After spluttering and stalling it did something that a first time poster called "a little backfire pop".
I would guess that it's more likely it was just a jerking, lurching stop-go-stop from the compression at ultra low speed.

Anyway I would probably start by checking the head gasket for leaks of combusted fuel by swabbing with a cotton bud or whatever, and check the crank seals visually and by smell.
I would then measure the cranking pressure with a gauge.

 

[Camden]

I don't think it definitely backfired. After spluttering and stalling it did something that a first time poster called "a little backfire pop".
I would guess that it's more likely it was just a jerking, lurching stop-go-stop from the compression at ultra low speed.

Anyway I would probably start by checking the head gasket for leaks of combusted fuel by swabbing with a cotton bud or whatever, and check the crank seals visually and by smell.
I would then measure the cranking pressure with a gauge.

When did I say I was going at ultra low speeds? The pop seemed like it was through the carb.
I've also tried every brand new spark plug I have, most of the new parts i've ordered came with one, I also have a couple of nice ngk plugs I've tried on it.

 

[gary55]

I would be having a look inside the cylinder if it's backfiring through the carb.

 

[JerboaJohn]

but it ran a bit when you got it and died, sputtering out? remove the head peek at the cylinder. does it smell really gassy? carb off, tank empty, tilt the bike all the way up in a wheelie, then do it on its front wheel. could be there's too much gas in the crank, it'd leak out the intake or exhaust like that.
just trying to help, scratching at ideas,,
this is off the wall, but something could be blocking the exhaust

 

[Vikingimike01]

I had that when I go in rain, my CDI stops working for a day. Also just randomly the kill switch turns on. Press it a few times.