The course looks to be down hill which will help keep an engine running at a very low RPM more so than climbing that same slight hill.
I wouldn't worry about the engine idling along without any real load and for such a short time.
Back out the idle speed screw on the throttle linkage to lower idle speed. You may need to provide more fuel with the idle mixture screw. Seems backwards but with the lower air velocity through the carb it has a harder time picking up that fuel, so opening the mixture screw helps get the necessary fuel in there.
After that smaller tires as mentioned and or some different gears are about all you have to work with. Idle speed then being the only practical method.
Good luck,
