I'm new to this engine, it is 15 years old and just recently came into the family as a basket case. It was running pretty good for a few days but started surging badly yesterday after I repaired the muffler. I somehow knocked the governed idle screw off! Amazingly, the engine started and didn't over-rev without it - but it surged like crazy. I replaced the spring with a genuine replacement and viola!
I also discovered that a Briggs and Stratton Diamond dealership is the place to go for unusual parts like this.
Glad to hear you were able to solve the problem. Like you I’ve preached on this forum that having and using a good dealership when trying to solve problems is far more valuable than the little bit more you might pay in parts.
