Morgan Colortune/Carbtune Tips
-originally posted by Mr. Larry D with notes from Mr. bwringer

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[Editor's note] When performing a vacuum carb sync or other tune-up work, use a temporary fuel source (or secure your tank) and don't forget to place a fan in front of the motor to help keep it cool while running stationary.  

[Editor] This is a Morgan Carbtune in use.  It's basically a "see-thru" spark plug used to adjust the color of your engine's detonation.

I cranked the idle mixture screw out about half a turn to demonstrate how the flame color turns yellow, then in again to show it turning a nice blue.  

[Editor] [Click here to see the video on Photobucket.]  You can also download the video by clicking here.  Be sure to install a media player that plays Flash video, such as VLC Media Player.

You want to get the flame a nice blue, then make it a little richer than that for best idle and throttle pickup from idle. I made the flame nice and blue, then backed it out 1/4 turn from there. We may do some more tweaking once we get a break in the weather and can test-ride the bike, but it's very close now.

In the video, the spark appears to be missing a beat every so often, but I think that's sort of an artifact of how the video was recorded.

We got the mixture screws very close simply by listening to how the engine idled down and how it reacted to "blipping" the throttle rapidly:

    * If it "hangs", meaning that it tends to return to idle very slowly, that's a sign the idle mixture is too lean.
    * If it "dips", meaning that it goes below idle speed (or dies) when you release the throttle and then returns back up to idle speed, that's a sign the idle mixture is too rich.
    * A lean or very rich idle mixture can also cause stumbling when you blip the throttle.
    * If you have an intake leak, you might also notice the lean symptoms of a "hanging" idle and that the idle speed increases as the engine gets hotter. An intake leak also makes the engine run much hotter than it should.

To use these indications, you have to be in the ballpark already -- clean carbs with clean idle passages and a properly sealed intake system, along with a healthy ignition system. If one of these factors is off, then twiddling the idle screws doesn't tell you anything.

Those brass vacuum port tubes are from my mercury synchronizer. The Morgan comes with these little plastic tubes that are sort of a pain to deal with. They work fine, but it's just easier to grab hold of the brass tubes.

Lastly, you'll note that the vacuum readings aren't totally identical. I think I ended up getting the 3/4 readings a little closer after Larry took the picture, but the important thing to know is that you can't ever really get this absolutely perfect -- you'll make yourself crazy trying to get everything exact.

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