Push mower RPMs too high with new blade

I have an older Murray 22” push mower model 96112005900 with a Briggs 5 HP. The mower is still in very good shape—regular oil changes etc., and over the years I’ve resharpened the blade several times so now it’s time for a new one. I took the blade to Home Depot and was shown a universal blade that looked almost like an exact match except of course both cutting edges had a lot more metal than the old worn-out blade. I installed the new blade and started the engine but when the engine started it ran up to what I would describe as really-high RPM speed and the carb speed/lever control has no effect. I do not have a tach but I thought there’s no way this is right and it must be something with the throttle springs or linkage or gov. I usually blow off and WD40 the linkage once or twice a year so nothing was gummed-up and the springs and everything seems fine. The odd part is when I put the old blade back on the engine RPM stabilizes at its normal level and the lever/speed control works normally. I can’t run the mower with the new blade as the RPMs are so high I’m afraid it’s literally unsafe even though side-by-side both blades look virtually identical.
Any Ideas why I’m getting this RPM difference with a new blade installed?

Looking up the machine, you do not have a separate throttle control.
 
To adjust the RPMs, there's a small spring in the linkages.  If you push the "tab" to TAKE PRESSURE OFF the spring, that will lower the RPMs.  Make sure it isn't binding/crooked, etc, before bending the tab...
 
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