You know what Jim, you're right, mine IS a Ryobi 31cc. I did the conversion to bike motor about four months ago and forgot that I got that motor from my neighbor's yard sale. The flex drive was broken so he sold it for $3. The engine runs much smoother on E85, especially at very low rpm's. It used to kick and buck a lot at the slowest speeds, but with the high octane rating of 105, that E85 fires better. I did a conversion on a Homelite 25cc a while back, it actually ran better on the bicycle downhill because it has no reed valve, the homie was piston ported. But the Ryobi 31 has more torque at low end, better for hills and larger props.