1972 mercury 200 20 hp throttle linkage binding?

i just picked up a mercury 200 20hp or dirt cheap i plan to put on a skiff, the fist problem i ran into is that the throttle wont open the carburetor all the way. the linkage stops moving when the spark advance ends, is like its hitting a stop but i dont see any. i got the motor with no tiller handle on it so i have been using the lever for remote controls to actuate the throttle. could this be a problem? also once i fix this how do i sync the timing advance with the carbs? i have done it before on larger thunderbolt ignitions but never one with points.
thanks for any help in advance!

A factory service manual is your friend here, will walk you through it.