Changed the plugs and it runs/fires well except when accelerating hard - it makes a deep throaty sound that it did not do before. Seems to not accelerate quite as well as before also.
The only thing I did differently this time was coat the threads with anti-seizing material (careful not to get any on prongs where the plug fires) and I tightened them a bit more, because when I was removing the old ones, they where just a bit loose and not as snug as when I put them in a couple years ago. The plugs say 19 ft. lbs to tighten, so I probably have gone over this.
Should I loosen them up a bit? or do something else?