High altitude jetting issues

[Poor boy]

Hi all I have a 66cc gas bike motor with a cnc velocity stack, high flow filter and a high compression head as well as an expansion chamber. I had the bike dialed with a 62 jet and the original pipe and intake but now can’t figure out the jetting for the life of me. I started at a 72 for a baseline and then went richer and leaner and I can’t get it. Do you guys have any suggestion for what I could do? I’ve done a 60-75 set of jets

 

[Wrench]

Try moving the needle clip,
Moving the clip up makes the bike run leaner, moving the clip down makes the bike run richer.

 

[wolframore]

I would guess that 62 is closer to what you need with the higher altitude, check your spark plug color for white being way too lean and black being too rich. Aim for a tan color.

 

[Poor boy]

Alright thank you all very much. It seems that I must have an air leak somewhere that I’m getting to the root of because I was lean on a 75 and I have virtually no porting going on :/

 

[Poor boy]

That was according to my plug which was grayish. The bike also ran correctly when closing the choke a bit

 

[mony0_3]

With engine running, spray carb spray into the drive gear area. If engine dies, you have a bad crank-shaft seal on gear side.

 

[Poor boy]

Ok thank you

 

[wolframore]

Carb cleaner sprayed around the intake area while running will reveal a leak when the RPM changes. It’s the usual culprit.

 

[Poor boy]

Thank you guys so much for the help. I’m still pretty new to this stuff and I appreciate the help

 

[Frogslayer]

Carb cleaner might actually hurt the seal behind the gear.