Hope my measurements are right. But on 20% o2 it pops, and the engine temperature correspond to the values, so it seems to make sense. When shutting throttle for gear shift or engine breaking the o2 runs to lean. If more than 20 it pops. I adjusted it for 18 and it works fine. The mix screw have had no effect on other value measurement.

The carbs are set up a bit different. I have a european model with other settings. My needle has both slots and spacer. Original jets are 125/47,5 , and theres a electric switch on ful lthrottle on the side of the carb. Se previous photo. I think it adjust for earlier ignition?

I believe the reason for the need for big main jet is less vacume and different pulse, together with more air volume. The large decrease in vacume is not present on the other side of the piston by the pilot jet when the piston is closed. Therefore, the situation is not so different for the pilot circuit with a KN? I do not know if it make sense?

Those numbers do not look like O2% to me. They look more like pounds of air per pound of fuel (actually, any unit of mass). 14.7 is nominally correct, varying slightly with the composition of the gasoline. Smaller numbers are richer; larger numbers leaner. Rich mixtures do not burn all the fuel, because the amount of air is inadequate. Lean mixtures do not burn all the air.

When I flew Cessna 150/172 airplanes, they had a mixture control. At altitudes below 3000 feet, the mixture was set full rich for takeoff. This is too rich, but is deliberate. The excess fuel does not burn, but it evaporates and absorbs engine heat. The engine is "fuel cooled" during takeoff. Once reaching altitude the throttle is set to the desired RPM, the mixture is slowly leaned until the engine runs rough, then richened slightly. On those aircraft with Exhaust Gas Temperature gauges, they were leaned until the temperature reached maximum, then richened till the temperature dropped 25 degrees.

Later, some experimenting was done on airplane engines for electronic ignition and such. It was found that as the mixture was changed, the high temperatures moved. At ideal mixture, cylinder head temperatures were highest. As the mixture leaned, the cylinder head temp dropped and the exhaust temperature rose. Apparently, the leaner mixtures burn more slowly, so are still burning when the exhaust valve opens, allowing more flame to pass the exhaust valve into the exhaust system. Bear in mind, these are air cooled engines running at high power settings, around 2400 rpm.

http://flighttraining.aopa.org/students/solo/special/mixture.html

If this works, it is an article on mixture control on airplane engines. It does mention automobile engines, and the information applies to motorcycle engines as well. It mentions the temperatures and burning rates of both lean and rich mixtures.

Airplanes are an interesting application, because they are about the only place where there is an operator-controlled mixture adjustment. And unlike automotive use, the engines are usually operated at relatively constant speed and relatively high power output.

I referenced the article to show effects of lean and rich fuel mixtures. Such information seems hard to come by outside the aviation community.

I use the term high power output to refer to operation at power settings of from two-thirds to full power. True, piston airplane engines run at low speeds of around 2400 rpm, but that is to keep propeller tips from going supersonic, and these days for noise reduction. The engines themselves can turn considerably faster, with greater power output. Looking into the airboat community shows that nicely. The boats using direct-drive propellers have either very small propellers or low RPM, while the ones using automotive engines run the engines much faster and use reduction drives for the propellers.

The LS650, operating at speeds in the area of 60 mph, is only making about 10 to 12 hp at its 4000 rpm. It is thus operating at about 1/3 to 1/2 power, depending on how much power it is credited with having in the first place. Most automotive and motorcycle engines operate for most of their lives at low power settings indeed. I suspect few would survive high power operations for any significant amount of time unless seriously derated.

Well,... based on Halvors general findings,  I've swapped my #150/52.5 set-up,.. to a #152.5/50...
Hoping for better mpg's and no loss at peak HP's..

Initial riding feels very much the same, and still smooth without popping...
Will have to do some longer rides with more elevation change to see overall...

We're getting a crazy amount of rain here right now...
My street was running 4" deep, full width, for two hours yesterday...(somewhere at the end of that flow, there should be a new lake)...
...

Hello, new 170 main + pilot 50. I have had only a short test run.  I may adjust numbers later

Idle + 3/4ccw =11
Idle + 1/1ccw =10,5
Idle + 1,5 ccw = 10
Cruising 80kmh + 1/1ccw = 12 (+0,5)
WOT 18-20 (nothing happend?????)

I will try to restrict the air flow with a sock over the KN filter. I will go for another and longer test run.

Halvor,.. is your K/N filter oiled?...
It sounds like you're just getting an uncontrollable amount of air at WFO...

When I tried an open air filter a couple of years ago,.. top end performance went way down for me...
I went back to an oiled slip-in K/N in the stock air-box...

Tried to restrict kn filter with tape. Have allso tried with original rubber tube. But it is lean on WOT. The lean condition has a time delay.

It feels like theres not enough gas entering the carb. I will open the bottom, place it on pri and see how it flows . Maybe this have been the reason for lean WOT all the time?

Cruising and idle o2 is the same for all air filter modifications.