Actually, just remove the HSN, open the carb, and spray (use a syringe) regular nitro fuel down the HSN hole (and/or again through the fuel nipple once the HSN is back in). Do again with carb closed. The gummy stuff disovels and will pass through the engine once it starts. However, the best way to clean a carb is take it off and dismantle it. I'm too lazy and the first method has always worked for me.