Dan it only takes a grain or two of grit under the reed to cause the engine to get weird. If you want to clean it first in the meantime. The important thing is to work very clean suggest using a white fabric on your work table.

Remove the engine completely and unscrew the needle valve, set that and the spring aside. The carburator on these engines is actually the fuel tanks backplate and engine mount. They can be run in four different positions (upright, inverted and on the right or left side) that is done by mounting the tank and backplate to the crankcase in four posible positions so scribe a small mark between the crankcase and the tank then agine between the tank and backplate. This will aid you in reassembly.

Unscrew and remove the four long screws on the backside of the backplate (these hold the backplate, tank and crankcase together) then carefully pull the backplate from the tank there will be a plastic fuel pickup tube plugged onto a nipple inside the backplate and a tiny spring inside its full length. do not disturb this tube as it must reassemble in the same position. Depending on its age the tube may be petrafied (Not flexable) but if the line to nipple joint is tight that is OK. Next pull the tank assembly from the crankcase. On the front of the tank is the valve assembly and if you look at it you will see there is a wire circlip holding a brass or clear plastic four leg star in this assemblys cup. by carefully grasping the center wire of this circlip with small pliers it will remove and the reed will fall out.

What is left to do is clean all these parts carefully by immersing in some alcohol then reassembly, any grain of sand under the read can cause problems. There is a center tube in the center of the tank that plugs into the backplate and at the joint a tiny rubber ring make sure this is intact. While the backplate is off you will see a tiny screen on the backside that is actually the carburators air intake that screen must be absolutely clear of debris. also blow out the fueling/vent tubes in the tank or the backplate not forgetting to blow out where the needle valve inserts.

Sounds complicated but goes fast once you see how it is done.

Enjoy

John