Small Engines (Lawn Mowers, etc.): lawn mower plug fouling, hp engines, throttle control

Question
Since the feds started messing with lawnmower design, every small mower I get (all with the B&S 5-6 HP engines) fouls plugs in less than an hour's run time. They are heavily carbon sooted, which means fuel fouling, IIRC. Since there is no longer a throttle speed control, how do you either increase engine speed or get the engine to run less rich? They all seem to run at just above idle now, which makes them lug heavily when cutting our dense country lawn.
I'm getting tired of buying plugs in bunches just to cut thelawn once.

Answer
Hi Tom,

Sorry, I have not worked on one of these engines.  If there is no throttle control to adjust or bend something and no mixture screws, I don't see how these settings can be changed.  Doesn't it feel good that our gov is looking out for us?

Good luck.
Michael