Hi, I have a 2000 M900S with adjustable Showas that I have been building, an upgrade from my M600. The stock Showa forks on my 600 felt fine to me in the sense that they weren't overly harsh nor did it wallow around like a Cadillac, and the chassis felt fairly stable and handled bumps well. However, I have never ridden anything with really good, well set up suspension. I wouldn't describe my 600 as having good feedback and it did feel like it drifted around when leaned over in corners and didn't really stick to a line.
I weigh about 155 lbs, which puts me in the right weight range for stock springs, but I have heard the progressive fork springs aren't very good and it is better to replace them with straight rate springs. Is it worth it to swap them out and what weight oil is a good starting point? They are adjustable forks so I can fine tune them after I get the bike together and riding. I don't want to spend much money on it but $100 for springs is doable if it will make a difference. I know I should probably just put it all together and ride it and then go from there, but I would rather take care of it while I have everything torn apart, including the forks while they are still disassembled. Thanks guys, Jon.
I'd say .80 springs if you're going to change 'em.
Throw some 7.5 weight oil in 'em and try it.