Re: 1970 Larson boat with a 120 hp chrysler OB
Disconnect the top link to the distributor and see if the distributor body moves freely. Because of the design of the interlock and linkage, if the distributor is stuck, stiff, or if the belt is too tight, the engine will either not shift into gear easily, not shift out of gear easily, or remain stuck in gear.
If the dist is stiff, remove the top pulley, remove the top circlip, and pull the body down and out of the mount. clean the body and mount, re-grease lightly, and reassemble. Then, pump some grease into the zerk on the side.
Do this with the engine at TDC so you will know where to set the pulley when you reassemble. (look at the top--It has an indicator line.)