I have read all the threads on using a couple of #4 washers to shim the needle. I have read "brass #4 washers" what difference if any would using stainless steel #4s make??? any help would be much appreciated

 

If I understand your question right....
Do not use SS as it is too hard and may damage the needle. Brass is soft enough to prevent this from happening. SS could create a ring on the needle allow increased flow and making it harder to tune.

 

Thanks for the help.