I finished my Ryca CS-1 conversion last week, and now I'm trying to get the carb tuning right. I'm curious to hear what jets other people in high-elevation areas are using. Ryca's official recommendation is as follows:

"After many trials we recommend in 9 out of 10 applications a 52.5 (stock) pilot jet and a 150 main jet for the CS-1 and other models with a k&n and a pipe..(55/155 is too rich usually)”

I asked them if living in Denver (5000+ feet above sea level) would change this recommendation at all, and they told me to start with 55/152.5, then back up the main jet one size to 150 if I notice any cutting out or hesitation. This seemed odd to me, because don't we have less oxygen at higher elevations? Shouldn't I need a smaller jet to get the ratio right?

Anyway, I ended up trying both pilot jets (the 52.5 stock one, and the 55 that came with the Ryca kit) and I noticed very little difference between them. The main thing was that I needed to use the choke to get the bike started on a 70+ degree day with the smaller jet, so I took that as a sign to put the larger one back in. However, I'm still not sure this is right, because once the bike is warmed up, I can't get it to stall with the idle mix screw all the way in (I couldn't do it with the smaller jet either). My noob understanding based on all the YouTube videos I've watched over the last few days is that if you can't stall the bike this way, your pilot jet is too big. Is it possible that both pilot jets are still too big, or am I just missing something?

Don't pay any attention to if you need a choke or not to start the bike cold.....some bikes like the choke, and some don't.  I have never seen that the pilot jet size has much of an effect on that.

The correct pilot jet size is the one that results in the smoothest running when the pilot mixture screw is 1.5 turns out.  If you can turn the screw all the way in and the engine doesn't begin to stumble - the pilot jet is too big.  If you have to turn the screw out more than 2.5 turns to get smooth running...the pilot jet is too big.  At my elevation of 500 - 800', the 50 or 52.5 is the best choice.....it depends on the bike and air cleaner setup.....muffler choices don't really affect idle mixture.  You likely will need a 50 or smaller.

Next is the main jet - a #150 is probably a good place to start at your elevation. , and unless the RYCA air cleaner does weird things, it should be plenty rich.  If you get a good strong pull at sustained full throttle....pay attention to what happens if when you begin to roll the throttle off.  If the bike feels like it is accelerating...your main jet is too lean - if you feel the engine hesitate or blubber a bit for a split second......your main jet is too big.  I tend to install a larger jet and see if the bike runs smoother, then continue installing larger jets until I notice it is just too rich.

The last thing to adjust is the height of the needle.  If you have surging and an uneven running just off idle to about 1/8 throttle, you need to raise the needle by reducing the size of the spacer on top of the needle clip.

You need to lower your idle speed a bit when you adjust the idle fuel mixture - it should be down around 800 rpm.  You don't want to ride the bike with the speed so low - but you cannot adjust the mixture with the engine at 1,100 rpm.....or you will experience exactly what you are getting.  At the higher idle speed the slide needle may be allowing some fuel to flow......and it masks what is happening in the pilot jet circuit.

Here are a couple of good videos that may help.

https://www.youtube.com/watch?v=YxpQjDQzX7g&t=16s

https://www.youtube.com/watch?v=zm5mB3R8Ucw&t=30s

Quick update now that I've had more time to experiment with the jets.

I still don't understand why, but the 55 pilot jet definitely seems to be the correct one for Denver. When I put the 52.5 (stock) one back in this afternoon, I found that I could turn the idle mix screw all the way out (almost 3 turns) without getting the motor to stumble. With the 55, the sweet spot seems to be around 1.5 to 2 turns out, so I've left it at 1.75.

I'm still not noticing a difference between the 152.5 and 150 main jet, so I've left the 152.5 in for now. I think my problem is that I'm not entirely sure I know what I'm looking for here, so when I have some more time, I guess I'll try an even larger main jet to see if things become more obvious.

I live in CO not too far from you, but at a higher elevation (7400 ft), and for the last few months I have been riding mostly at 6500 up to 7500 feet altitude. I have the stock carb with the stock jets on my 2015 S40.  It is also running with the stock exhaust. It runs well, but I used to have a lot of afterfiring on closing the throttle. I took the plug in front of the mixture screw, and the screw is now at 2 1/2 turns out. The bike runs very well and I have no more afterfiring. I don't think the bike is running rich. Maybe I am just lucky, but the carb settings which are lean at sea level just seem to work fine for me at high altitude with just an adjustment of the mixture screw.

I hope you get your bike running well soon. Good luck.

Mike ,you need to read Dave's first post above that's where he describes how to set your idle adjustment ,not by turning it and driving the bike! You can however test the main jet, run the bike in a higher gear with wide open throttle,then close the throttle by 1/8 ,if the bike speeds up the main jet is to small,(the bike is going lean), if the motor bogs ,the jet is to large (the bike is to rich).