I have a Honda lawnmower Model HR217 that I have had problems with bad gas and mower wouldn't start. I drained the gas, pulled the carb and cleaned it with a spray carb cleaner and reinstalled and was able to get mower to run at full throttle but not at low throttle. I took the mower to the local shop where I purchased it and had them work on it and they told me that they had to de-carbon the engine, after getting it home it now runs at a higher rpm than before but still no low speed. It will run for a little while and then acts as if it is running out of fuel, begins to backfire and then dies. I can remove the gas cap and then reinstall it and am able to crank engine with throttle choked and continue mowing for awhile until scenario occurs again.