The design of the inslulator block under the carb leaves a little to be desired...They should have put 2 more bolts in the middle...The distance between the hold down blocks makes it easy to tighten the bolts too much and warp the block in the middle....The new blocks seem to be better than the older ones..I fixed some by sanding all the surfaces perfectly flat, then using some high tech Permatex anaerobic gasket maker (sparingly) on all the mating surfaces...
Check your bolts, maybe they're a little loose...
Don't get any of the sealer in the pulse holes...
DA uses G10 epoxy board, much stiffer...
You might also clean the block and look for a crack somewhere around the bolt holes...