tips for electronic tuning with an oxygen sensor

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Keys to a good tune!
The key to being proficient with the EJK is a good understanding of the modes and the lights, both the color and the flashing frequencies. Our first attempt with dyno load and no adjustments showed an air/fuel ratio on the Koso gauge of 12.5 at full load. This is a little rich, as 14.7 is often quoted as ideal, but that relates more to 4-strokes. So 2-strokes may need a little more fuel for cooling and lubrication.

After some adjustments on the top end, we got the air/fuel ratio to 13.5 and gained 5hp on the dyno. This showed that the stock fuel calibration is rich on top end, but Rob’s sled only had a few miles on it and was possibly still in the “break-in” mode. The 5hp gain matches reports of a similar gain once the Polaris is off the break-in cycle.

The good news was that we could change the air/fuel ratio by a substantial amount with the Dobeck tuner, and that it showed up right away on the Koso gauge and on the dyno reading.

There is, however, only so much you can do on the dyno. Real-life load conditions often are more transitory during acceleration, depending on the weight of machine and driver. As a result, final adjustment has to be done when testing in the field.

Rob will give the setup a good try this winter, and we will be greatly interested to find out whether this combination of air/fuel ratio gauge and EJK tuner is easy and practical to use.

Many questions remain about whether the air/fuel gauge is easier to tune by, or if the EGT gauge proves more reliable. We will install both on our trusted test mule this winter. It will be interesting to see what we find with the two instruments operating side by side. Stay tuned for the updates!
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