Carb tuning

[huunz]

I've got the 650 Spider, the one with the two cylinder engine and side draft carb. The right plug was cold/not firing, so I changed the plugs out (thanks Silverbullet for the plug type, and this forum for how to do it) and then tackled the intake. When I pulled the air filter tube off, there was standing gas in the carb inlet. Because of what I found, I took off the carb top, cleaned the needle and seat, although they looked fine, and put it back together. I started it up and it ran great. BUT.... if i wanted to change the needle and seat, say to a Viton setup vs. the solid needle, where would I look? Do any Japanese bikes or quads fit? I found the oil filter is the same threads as my 91 Nissan 2.4L pickup, so other parts might cross as well. One issue i can see is that carbs have not been used on cars in the US since about 86.