I had a similar issue and this is the path I took. Did you remove the spring?
I'm assuming you removed the throttle assembly during cleaning and inspection. One or both of those mounting bolt holes are slotted and that's how you adjust the engine speed. So if you took that off and didn't put it on precisely where it was, which I found to be difficult, you will affect the spring tension and engine speed. I found this video helpful when it happened to me.
I made small adjustments with the engine off. Then start it, check with a tach, rinse and repeat until the RPM's were at spec. If I remember correctly, it's 3600 for that engine at full throttle. Other's may know how to do this with the engine running but I didn't have the confidence to do that fearing I may over-rev the engine.