The power valve closes around 7500 RPM, it helps the motor out of very slow corners by changing the exhaust port height but most of the time it’s closed. The burnt exhaust packing will reduce power because (I think) the stinger is effectively shorter or even non-existent depending on where the packing is leaking. The difference will show up on the stop watch, maybe as much as .5 sec.
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Thanks for the tip ! What kind of packing do you use? Brand ?
Another question if i may about the Mychron laptimer. Does the live Delta function only comes with the model 5 ?
Its a Rotax part. Buy from a shop that supplies Rotax parts.
If you are referring to function that shows how much time you are either ahead or behind on the current lap when compared to the best lap on the MyChron display. The MyChron 4 with speed sensor can also provide that information on the display and as so can the My5.
FYI -
The matting on the EVO pipes doesn’t burn out anywhere near as fast as the old style pipes. Still good to check it periodically, but you might not always need to replace it.
Same goes for power valve maintenance - it’s always important, but the EVO power valve is much less likely to stick than the original power valve.
The newer clutch drums are also an improvement over the older style - they can still crack, but again, it happens less often. I always have a spare on hand - but mostly for wet conditions. For example, at my home track which is tight, we use a 12 tooth front sprocket in the dry. My spare has an 11 tooth sprocket on it. I do this because it can be quicker to change out the clutch drum to one sprocket size down and still use the same chain, rather than adding rear teeth and changing the chain (on my track you can’t go bigger on the rear without bottoming out) to get the same gear ratio change.
The one thing on the clutch side that hasn’t changed is you’ll want to keep the needle bearing in the clutch lubed.
The EVO upgrades were pretty good at easing the maintenance pressures on the users (wiring harnesses aside - but they work until they don’t - not much you can really do maintenance-wise for that). If you’re competing at a National level, you’ll still want to spend the time to go over things, but at a club level, you can pretty much race it, put it away at the end of the day, and not worry too much about it when you’re ready to go again.
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Thanks Rob! I appriciate your time to help me with the unknown 
It doesnt matter at all.
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Square is a little easier to adjust because it typically takes a 13mm spanner/wrench.