RE: Adjusting the low speed?
I'd suggest other possible solutions. You obviously know how to tune your engines. Any change from what has been normal on any engine suggests to me a speck of dirt in the fuel metering system or old fuel which has lost some volativity. If your fuel is fresh and of the proper oil and nitro content then there might be dirt in the system. Start from the fuel tank and go forward until you find the problem. A tiny pinhole in the fuel line can cause the problem too. Flush the carb and I'll bet you'll be in business. Oh...change the plug too. Mitch