Hi can anyone help I recently got a k75s and I'm noticing a popping similar to a backfire but not that loud when I shut off the throttle going downhill any suggestions or ideas would be very much appreciated then in advance

Quite normal for the K75 try a new gasket on the muffler to header slip joint.

+1 on the header to silencer gasket.  You might also want to check the adjustment of the throttle position switch(TPS) and make sure the "choke" is fully closing when it's turned off.

You also want to make sure you turn the throttle completely off when coasting.  I know this causes a lot of popping and backfiring because I had a habit of not fully closing the throttle when engine braking.

I cured mine after many years of playing around with it, doing the following.
1/Fix all vacuum leaks.
2/Fix all exhaust leaks. Header to muffler can be hard to seal.
3/Adjust the TPS.
4/Adjust the mixture.
5/Make sure that the injectors are clean and have the correct spray pattern.
6/Make sure fast idle is off.
7/ Fully close the throttle on overrun.
You still might get an occasional but very rare backfire, probably because you haven't closed the throttle.
Regards Martin.

I've learned to live with it.  It provides a bit of Kharacter to the S. 

Prob a long shot but quick check,  which spark plugs are being used,  which leads? Can sometimes be as simple as lose,  dirty or poor leads. Poor leads crossed,  something like that, I don't like them touching.