big twin will not throttle up in forward.help

[hambone]

i have a 1963 evinrude big twin 40 hp. the motor ran fine a month ago. i had to replace the shifter rod a few weeks ago. so i dropped the mid section from the powerhead, replace the part and put it back together. put it on the water a week later. and it will not throttle up in forward gear. it throttles up fine in neutral. any help would be greatly appreciated. iam not looking to spend a bunch of money on this motor, so iam hoping i can do this my self

[boats.net]

Check to make sure you have spark on all cylinders and fuel to all carburetors.