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Experiences from a highly qualified German tuner (Pirate-Racing) with mainly 690 engines is that without exception any shorty loses power on single-cylinder engines.
For looks/noise yes, go 4 it, for power output keep them longer.
 

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According to this tuner, an electronic aid won't improve a shorties performance over a large volume can.
He has good results with Leo Vince silencers.
I think you can also have a look at the MIVV products.
What is the objective of changing the exhaust?

Or in saying that would I still lose power if I added the shorty and a ecu piggyback to tune it for that specific exhaust? Thankyou for your information I'm new to the duke world only owned bigger bikes in the past and never had these problems
 

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An often heard generalisation.
Yes the Dukes are on the lean side IN THE CLOSED LOOP determined by the O2/Lambda sensor.
Outside the closed loop they run slightly rich.
This is why a B-plug isn't the best solution as, although it aids in the closed loop sessions it also makes the open loop even richer.
In the long run the excess fuel washed away the lubrication on the cylinder wall and the bike performs less due to a too rich mixture at higher revs (open loop).

".....Bigger bikes", or older bikes; that were not fuel injected - and likely not as constricted up / bound by emission's laws as some (THIS !!!) 'modern' motorcycle(s) ?

In saying that - i agree with you. The 390 is quite a fickle beast fuelling-wise. And even compared to other modern bikes i've owned - does run particularly lean as standard. So any opening up / work on the breathing side and / or exhaust is likely to lean it up even more........

Good Luck ;)
 
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