VES spring change question

It would be worth doing a plug check I think. At the most you may need to adjust your needles a notch. A lighter spring may not close as quickly either. What spring are you using and at what altitude?

My concern with any of these is that the solenoid is holding the valves shut until a predetermined rpm. The idea of a VES (variable exhaust system) is to have a smaller port opening to create more low end at slower speed. As rpm increases the port height increases. With the solenoid in control it holds the valves closed until you start to have an engine choking situation. I believe they do this to meet EPA regulations. With the lower port height they can then supply less fuel to the motor at a specified rpm. This should be the lean spot where the EPA tests emissions.
On carb models it should be a simple needle adjustment. They jetted it to run with the solenoid. You have taken that out of the picture. Do just a short mid throttle run at about 6500-7000 rpm then shut it down and see how the plugs look or check your piston wash.
Have you tried running it with the stock springs and solenoid plugged? That might do the trick itself. Otherwise check this thread for spring rates. I think they were on page 2.

sidelinellc said:

actually i have the solenoid ports plugged off already.
You make a point i have not heard of yet, a possible lean condition just as valve opens due to this mod if i understand correct, i have run it like plugged off since new and even jetted down to 410's. plugs are always chocolate to black. the needle clip adjust is something i hadn't even considered.

So, if i understand correct, by lightening the spring rate, =valves open sooner in the already lean mid range possibly causing a leaner flow thereby cooking? am i off base hear

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That is how I look at it anyway It is a consideration that I would pay attention too. The 600 may not be as finicky as the 800's, but it never hurts to make sure everything is dialed in.
Sounds like you are running somewhat rich already? So I don't think I would be too worried. What altitude are you riding at?
You are correct with the valves opening sooner you are changing the motor requirements to some extent. It is minimal, but always worth checking IMO. You will be increasing exhaust flow so you hypothetically would want to increase fuel flow. Again, I think this is minimal. Remember, if they open too soon you will actually hinder low end performance.
Keep us posted on your findings.