Engine Trouble YD100 cant start and makes weird puff noise

[emtihc]

Hey guys I've got a new problem with my YD100.
Its always been a pain to start but recently it hasn't been starting unless I pedal up and down my street like 15 times.

I pedal up as fast as I can, drop the clutch, and then it sounds like nothings combusting and then I get a big puff noise and it stalls. Someone said they saw a puff of smoke/mist out of my air intake when the puff happens but I'm not 100% sure if thats happening.
After about 10 times repeating this, it eventually get going, but then boggs out, looses power, makes a big puff noise and stalls.

I've got a video below of me pedaling at about 20kph and then dropping the clutch. You can hear it backfire a bit and then make a puff noise.
Does anyone know a solution?
Thank you.

 

[Chainlube]

Tighten down the head.

 

[GW's Motorized]

Tighten down the head.

Yup. The backfire is probably the intake port still being open when it fires. The port timing will be off if the head isn't tight

 

[mony0_3]

The exhaust might be restricted.

 

[emtihc]

Tighten down the head.

Its as tight as it'll go unfortunately. If that was the problem wouldn't it backfire even once I get it fully warmed up?