This has my head spinning, We were trying to get a box of bits going, Some time ago, I didn't want to fit the P/tank, So left the front carb' top off, And filled with petrol, from a can, It worked OK doing this with a Comet !
But with the Twin it only got petrol to the rear, After holding the front float down !, I was not thinking right, But it worked, I was thinking the back pot was not as good as the front, Silly old ---.
So what I am saying is, it sounds like the front needle is not seating right ?.
Sorry , I type as I think, Slow !.
Cheers Bill.