Valve Adjustment Doesnt Work

[Husq yth21k46]

I own a Husqvarna YTH21K46 2 Cylinder. My question is when both sparkplugs are in, the engine locks. But when I remove one sparkplug it starts no problem. I already did the valve adjustment with the tool that you use for adjustments (6). What am I doing wrong? Next step? Help!!

 

[ILENGINE]

And what Genus and Species is this engine. Without engine numbers my Covid exposed brain can't see what you are talking about.