F60 2004 Carby Model (flat spot)

[captain rednut]

Hi guys Ive got an engine giving me grief, the engine starts great and idles perfect but has a very bad flat spot on acceleration and low on power but you get through this spot if has heaps of power and performs to max rpm.
I feel its in the carbies but ive been through them several times and cant find anything that gets my attention.
I'm aware the have very small passages in the bowls which clog up which are clean but is it possible the seats are leaking through the o-ring under them and how do i get the seats out of this model??
Any other thoughts as Ive changed almost everything.
Regards Jim

[rodbolt17]

two things to look for.
make sure the acceleration system and that stupid check valve are working properly.
and make sure your using a 4 channel manometer when syncing the carbs.

[captain rednut]

Check Valve

The check valve appears normal in a liquid test but im not sure if you have a better way to test it??

[rodbolt17]

that system works by raising the air pressure inside the float chamber via that funky diaphragm assy on the top carb.
there is a non serviceable valve in it.
this system does NOT like slow throttle up.