Carburetor Modification Part 4

One of the benefits of installing the smaller Scrambler tank is, since it is physically smaller and sits higher on the frame, I can now perform all the carburetor tuning without having to disconnect hoses or prop the tank up. Following the results from the last round of carb testing, I determined that the idle/slow jetting is slightly rich (fixed by adjusting the air screw), the midrange is too lean, and the top-end of the bike still surges and stumbles.

Much more room now with the small tank

 I solved the midrange problem by installing the next higher-size needle jet (P-6). For the top end, rather than change the jetting, I reinstalled the sheetmetal baffles in the float bowls and lowered the float height. Both of these steps will lean out the mixture (and make the carburetors stop leaking fuel!)

The shakedown ride I took following these changes was encouraging. It now idles perfectly and accelerates strongly right off the line. There is still some stumble at full throttle, but it can now cruise at 60-65mph with no hesitation. I'm sure the correct setting is within reach, but I'll have to wait for warmer weather to really open it up and test it. The current carburetor settings are:

Mikuni VM26-8074

Main Jet: 130
Pilot Jet: 35
Needle Jet: P-6
Needle: 5F21
Air Jet: 2.0
Slide: 2.0
Float Valve: 2.5
Air Jet Turns: 2
Needle Notch: Center
Float Height: Approx 17mm

Hard at work with a cup of hot tea