Just got back from getting my P650 Dyno'd at a local shop...I did 3 runs using 3 different airbox lid set-ups. This shop just got a brand new Dynojet brand ATV dyno...its so new, they haven't had a chance to hook up the printer yet, so I had to take notes of the results. They said I can come back at a later date to pick up the print out (after they get the printer set-up).

MY CURRENT CARB SET-UP
First, I'll tell you that I made the following adjustments to my P650 in hopes of using the modified lid (aka "swiss cheese lid").
1) Shortened both Needle Jet springs by 3/4"
2) Polished both Slides
3) Added an extra shim to my stock needles (now have 2 shims on each needle)
4) Increased the Kehin main jets to 155/160
5) Readjusted the idle mix screws to get the highest idle speed...ended up 1 and 3/4 turns on both screws (which seemed a little too lean to me at the time).

MY RESULTS
First off, let me say that this Dyno did not have any specific software to account for CVT transmission, so I believe the following max HP and max TQ numbers are probably way off. However they should be useful for comparisons of the 3 different airbox lid settings and also to see the smoothness of the HP/TQ numbers. In addition, the A/F ratio should also be fairly accurate regardless of the lack of CVT software.

I did 3 runs using 3 different airbox lids as follows: 1st run is with the SWISS CHEESE LID, 2nd run with the STOCK LID (no holes), and 3rd run is WITHOUT A LID. To get the Dyno to read my air/fuel mix, I had to remove the 14 discs that I currently have in my supertrap pipe (they had to insert a tube into the muffler to pick up the readings). This may have leaned out my a/f mix a tad bit, but probably not much b/c I already have 2 more discs than the max # recommended by supertrap.

RUN 1 (swiss cheese lid)
Max HP - 30.65 (at ~2,000 rpms)
Max TQ - 24.18
A/F Ratio - Started out too lean at idle (13.5:1), then hit 13 at 2000 rpms, then continued to get richer to a tad below 12 at max rpms

RUN 2 (stock lid - no holes)
Max HP - 34.05 (at ~2,000 rpms)
Max TQ - 27.53
A/F Ratio - Started out too rich at idle (11:1) and continued to get way too rich until max rpms (jumped off the screen below 10)

RUN 3 (no lid)
Max HP - 23.21 (at ~2,000 rpms)
Max TQ - 19.83
A/F Ratio - Started out WAY TOO LEAN (17:1) and continued to get a little richer until max rpms, but still WAY TOO LEAN AT ALL TIMES (richest reading of 14:1 was at max rpms)

COMPARISONS
Swiss Cheese Lid
The closest one to the "ideal" 12.5:1 a/f ratio was the swiss cheese lid and it also performed the best from 3100 rpms til max rpms. It also had the smoothest power curve (pretty smooth curve without a lot of bumps/jumps on the numbers).

Stock Lid
This one had 4 more HP than the swiss cheese at 2,000 rpms and continued to do better than the swiss cheese lid until 3100 rpms where it fell off at a faster rate than the swiss cheese lid and also was more spikey/bumpy.

No lid
This one performed the worst from bottom to top. It is clearly getting too much air and needs LOTS more fuel/fatter jetting to get it to work right without a lid. I don't really care to run without a lid anyway b/c many of my XC races are held in very wet/muddy conditions and I don't want to have to rejet for dry races with a lid on.

MY PICK
I really like the low-end grunt power of the stock lid, but also want the better power at mid range and upper rpm range that I got from my swiss cheese lid. I'm also happier with how smooth it ran with the swiss cheese lid. At this point, I think I like the swiss cheese lid best even tho it clearly has much less max HP/TQ at the bottom than the stocker. Even before going to the dyno today, my seat of the pants could easily tell that the stock lid had much more bottom end power and the swiss cheese lid had better mid-range/top speed. I need to change the jetting and/or modify the swiss cheese lid to get it richer at the bottom end and perhaps a tad bit leaner at the top end.

Any suggestions??? I think I need to adjust the idle mix screws to ~3.5 turns out (like it usually is), add another shim on my needles (that would make 3 shims) and also decrease my main jets to 150/155 and add a few more holes in the swiss cheese lid. What do you guys think?

 

It would be my guess that you probably have enough holes in the lid. Since you have a dyno run to go off of , wish I had one close, I would recommend dialing in the jetting. I am a little surprised at how much more power you made with the lid on. With the kind of riding I do I always seem to have plenty of low end but like you I enjoy the little extra from mid to top end. In my opinion top end is the only part that is lacking in the motor tranny setup on the prairies and the brutes. Good luck hope you get it all lined out.