Engine braking?

[Frogslayer]

Lots of dirt bikes do have oil injection

 

[mark20]

Lots of dirt bikes do have oil injection

which ones? all of the 2 stroke dirt bikes i see you have to pre-mix them

 

[The_Aleman]

I don't know how you'd engine brake with a centrifugal clutch.

Missed this sentence, was pretty close to those pictures!..Will, centrifugal clutches can still provide engine braking above their engagement point!
Sounds pretty gnarly when they do. Every 4G-type system without a freewheel will engine brake.
The drawback of that (jackshaft system without freewheel), is pedaling with the engine off will turn everything to the clutch bell.

Even a Q-Matic, being an under-driven centrifugal clutch design, will engine brake. Here's my brother on the first retail Q-matic:

which ones? all of the 2 stroke dirt bikes i see you have to pre-mix them

I'm by means no expert at all and cannot provide any examples off the top of my head, but oil injection is on some modern 2-stroke bikes.

 

[Frogslayer]

Old as well. My first bike, a 1980 Suzuki 80cc i can't remember the model RS maybe had it. I had a 70 something Yamaha at1 125 that has it. Yamaha blasters were oil injected (4 wheeler but 200cc 2 stroke). Pretty much every 2 stroke snowmobile that's not strictly race only. Oil injection is common and it works. On some snowmobiles they even had an oil injection to put oil right to the main bearings as well as into the fuel air mixture.