Adjust mixture for highest vacuum on each carb

"Adjust mixture for highest vacuum on each carb"

any truth in that?

 

Not really.

Adjusting mixture won't directly affect vacuum until you begin to stall or race the motor by being way out of adjustment.

You adjust the throttle butterflies to MATCH the vacuum at each carb; then fine-tune the mixture for optimum performance. This may affect the vacuum sync slightly, so it pays to re-touch it. But we don't vacuum sync using the mixture screws.

 

To expand on what Fitz said:

As you improve the mixture the engine will run faster (without opening the throttle plates) so the vacuum will increase. This will happen across all the cylinders, not just the one being adjusted.

The effect is small and not a practical way to fine tune the mixtures. You're much better off with a color tune plug or sensitive digital tachometer.

 

Additionally,

You will end up too lean if you do that (tune for highest idle/vacuum)

The bike will bog after sitting at a red light.
You will have white plugs, with little of the tan-brown needed to keep from hole-ing a piston, burning a valve, or smoking the thin oil sheen on the jugs.

But it's valid advise for tuning a lawnmower, weedeater, ETC.

 

thanks guys.. was reading it at an xs blog where they were having trouble with their bikes running with the colortune plug in.

 

Early ColorTune Plugs had a serious problem with the High Tension Lead being insufficiently shielded from arching and shorting-out to the Cylinder Head.

Try adding some additional insulation to the HT Lead.
Heat Shrink Tubing or Electrical Tape.

The manufacturer sent me a better HT Lead when I phoned them and alerted them to the problem I had with the original one.