Checking your tuning

5 Sept 05

The ideal way to check whether a bike is in a proper state of tune (the mixture is correct at all places in the RPM range) is to run the bike on a so-called gas dyno. This is a dynamometer with an exhaust-gas probe. The bike is run against a load and the exhaust gases are measured for CO content. There's a certain range which indicates ideal mixture settings.

A handheld gas analyzer can also assist here.

If you don't have access to either of these tools, you can perform the following test:

1) Ride the bike on the open highway for about 5 miles, keeping in the upper 2/3 or the RPM range. A steady-state throttle setting works best here.
2) Pull in the clutch and kill the engine with the "Run-Stop" switch. Don't allow the engine to slow the motorcycle and don't close the throttle until the engine stops.
3) With the clutch still disengaged, pull to the side of the road, using the brakes to slow the bike.
4) Turn the keyswitch to "OFF". Allow the bike to cool down for a few minutes.
5) Remove one plug at a time and examine them.
6) A light brown, grey or tan plug indicates correct jetting.
7) A black, sooty condition indicates a mixture that is too rich.
8 ) A white or blistered electrode indicates the motor is running too lean. Should this be the case, go up 1/2 size on your main jet (for starters) and raise the jet needle by approximately .020" (via shim or adjustable "clip", if your bike's carbs are equipped with that type of needle)
9) Repeat the test after rejetting.

I'll be happy to go over this either via e-mail or on the phone should you have questions.

Contact Bagger John at http://www.xtremecruisers.com/cgi-bin/yabb/YaBB.pl