hi guys a recently changed the crankshaft on my BR500 as the bearings where noisy and machine didn't sound great so I took it apart it works out for about an hour then it started to lose power then heard a band and smoke came out of the blower tube anyone got any ideas on the problem at all...

Is the engine now locked up?
 
Compression?
 
Your going to have to do some digging, back track what you did..
 
.

no its locked up it still pulls ok just wondered why it died and the smoke came out could it be the carb 

changed the crankshaft with a genuine brand new one but the piston was after market but shawls can't be that 
 

Carb wouldn't do what your engine did. 
 
What's the compression, does it have spark?
 
Everything look ok under the valve cover?
 
.

don't have a compression tester ill check other things in a while 

think I found the problem this had come of the carb can't see anything else has compression spark and valves all good just adjusted again 

impulse hose came of carb
 

Impulse line would do it...  Glad you found it..
 
.

Thanks for your help pal its must appreciated 👍👍