I've got 1500 miles on my S-Jr. The first tank or so was around town and it seems the mileage was up about 1 or 1. 5 mpg above my norm of about 17, but I didn't have a chance to do a fillup before leaving for Az for Christmas. It also SEEMED the overhead was closer to actual than before judging by the number of miles to the 1/2 mark on the gauge. It's normally at least 2mpg high, sometimes 2. 5 or more.
On Dec22 we left for Flagstaff from San Diego and I did my first fill in Yuma. Prior to that I had done a partial fill with enough to get to Yuma as it's 35-40 cents cheaper there than San Diego. That gave me 863 miles, about 650 of that with the S-Jr installed on the "economy-40hp" setting and I drove the 150 miles to Yuma at an honest 75mph all the way even when climbing through 3500 feet of elevation change. I got 17. 4mpg. From Yuma to Flagstaff, about 335 miles, again at 75mph all the way, even from Phoenix to Flag which is a 7000 foot climb plus about 120 around-town miles gave me 15. 1. I did the Flagstaff-to-Yuma leg, 335 miles, in just about 4 hours and 45 minutes of actual driving time, or right at a 71 mph average , with several short bursts at 80mph or so.
The last full fill was exactly 18mpg hand calc. I've never gotten better than about 16. 5 before in similar circumstances. Interestingly, the overhead read 18. 5, closer to actual than it's ever been. I haven't filled up since getting home, so can't comment except to say the mpg is down a bit because the last 150 miles home includes a section of I-8 that goes from sea level to 4500 feet in about a 10mile stretch and I did it at 70mph on cruise, which didn't help the numbers any.
I have a Roktek timing adjuster that was on the full advance setting leaving home and put back to the stock setting coming back. I was concerned it might have too much timing in combo with the S-Jr so I played it safe.
Not bad for the speeds I was going in a Mega-dually-G56 at around 9000 pounds running weight. It now has 36,000 miles on it.
Great throttle response, really great passing power on the highway, and a lot more low speed smoke at high altitude; a little less so now that I'm home and running between sea level and 1800 feet,
but still more than stock. It idles at 800-850rpm now instead of 750 stock. Any more comparisons betwen 40 and 70hp out there? I'm curious, especially about smoke output and/or mileage.
I'm happy.
Bruce