Try bumping the throttle stick up a few times before starting your turn for final approach. It will usually knock the idle down. I've seen this on my Perry pump with Moki 1.80. You can usually bump the idle trim down a few clicks as well. I believe this is caused by the engine idle going lean since it's at the end of the tank. If you bump your throttle trim down a few clicks it will usually be too low when you refuel and start the engine again (because it's rich). I don't have this problem with my Moki 2.10 and Cline regulator. Do a few approaches trying what I recommended to see if it works (but don't actually land). There is also a idle down mix on the Futaba 9C that can be used for this but I never tried it. It uses a switch to go to lower idle. After a while you will get the routine down. I see this on my YS 63 as well (idle changes from full to empty tank).