Burning tips off plugs

Hey guys Thanks
I changed the plugs today, glad I have a rack! The only 2 burnt off were in the 2 front ones 1&2 cyl.. When I had the engine in my Daytona S/G car, several were burnt off, but that was a different tune up..
They are all black, like I said, I have been driving it in and out of trailer/shop.I did wire bru=sh, and no sign of balls/metal etc.
Normally they DON'T have any balls on them or metal, and they are nice and tan/beige.
I run Sunoco 110
I already went to the Autolite 3924 which is colder.
With everyones great input, I am going to also go up 1 number in the front jets only.
Read the plugs after the TT and if its looking good, I will leave it alone and watch them through the season.Atleast the 2 front are super easy to get at.
If they look unhappy,I will go back 1 degree on the timming, which at 36 isn't that advanced.
Like many said, I think I am just on the edge, and as I said, it ran the fastests it ever ran with the 2 bad plugs, so it's not serious.
Chris