F150 throttle spring tension

[shipmaker]

I have twin f150 using the 704 controls, the throttle seem to be stiff ever since i've owned the boat, so I replaced all the cables with teleflex xtrem , but still stiff to operate, when i remove the cable from the throttle leaver on the engine everything's smooth as silk. it seems that that the throttle return spring on the engine throttle to too strong and hard to open, is there a way to adjust the spring tension on the engine? No corrosion on the throttle assembly all clean.

Thank for any help,

Richard

[rodbolt17]

no tension adjustments possible on the motors.
fuggit abuut it.
however there is a throttle tension adjustment on the 704 box that can be loosened or tightened as needed.
old style box requires the removal of the plastic cover.
later premium 704 box has a plug aft and low on the plastic cover.
one pencil eraser sized slotted head for each lever.