OMC Interupter switch

[good to go]

First off I am a Newbie to the site, but view it all the time. Its probably better than a manual. I know there are all sorts of posts and literature on the OMC interupter switch/shift cable adjustment but I have not come across my particular situation. 1987 omc cobra hooked to 5.7 gm engine on 25 foot peterbourough cruiser. Shift cable force is 3.8 lbs, red cable. distances all confirmed on upper and lower cables hooked to the bellcrank. Dilema...when shifting at helm(single shifter) the interupter works the way it is supposed to for changing gears, yet there is a range beyond the shift and acceleration that the upper shifter cable allows the bellcrank to still move lower shift cable, this binds the trunnion on the lower cable and again activates the interupter. Is there some changes somewhere on lengths of the settings which will overcome this. I hope I have explained this so its understandable..Thanx for any comeback