HI Tom , How are you ?
Yes weird deal , I suppose .
This ONLY happens in 1st gear at a start.

Baseplates dont seem to be warped on a flat table , I usually use a hand nut driver to titen the carb bolts .

I manually drew open the carbs so I can observe my outdboards opening and snapping shut .

I just confirmed , both outboards crack open a " c" hair when i open up the center . Engine is cold .

I readjusted my rods lengthened / shortened to double check their placement , still same result outboard crack open.

with engine running ,they DO NOT open .

Heres the weird thing that leads to Possibly a vacuum leak somewhere .

I have a gage hooked to outboard tees . cruising and tipping in slightly on acceleration on any gear other than 1st , I read 2.5-5"" of vacuum and
you can feel the the outboards opening .

I might need to learn how to vacuum test the carb itself.

The first gear issue happens with Polyglas OR wide fat sticky tires . So The engines definitely under load on a burnout.

Im not sure if this is because of a short 1st gear ( passon OD )
Im chipped at 6500 , maybe i should go 7 ..

ill test the secondarys after a run around the block and see results .