Engine "missing" - B&S 3.75 Push Mower

[BHENDERS]

Engine will not run at steady RPM. It "misses" or "hunts" so to speak. Never stalls out, never fails to start. New plug, properly gapped at .030. This is a Model 98902 1110 E1 from an MTD push mower. I probably have a good 20 years on this mower, but just for my own mowing, fairly modest usage over the 20 years. I have confirmed that the gas is fresh. Could this be ignition ?

 

[Rivets]

Could be ignition, but I’m thinking that if you have not replaced the carb to tank diaphragm and gasket I would be starting there.

 

[BHENDERS]

Rivets,

Many Thanks ! The diaphragm gasket looked OK, but for the small cost, I will replace it before I assume an ignition problem. I was an instructor too. That is an excellent qualification!

 

[ILENGINE]

Also something to keep in mind is some of those engines used two governor springs, and if they get out of sync or the small one get broke or removed can also cause surging.