The electric quad bikes come partially assembled , unfortunately the chains are set too tight, this puts a lot of strain on the motor 

and makes it smoke ,

 the adjustment is the same as a push bike

please adjust the chain by loosening all axle bolts and moving the adjusters so the axle can move forward so loosening the chain,

allow 1/2-3/4" up and down play on the chain, then retighten all bolts