Ah yes the famous Cobra shifting problems, I had a problem with mine when I first got it too, what was happening was that it would shift into gear OK but would not come out of gear into neutral. I took it to a good OMC mechanic 4 years ago and its been shifting fine ever since. You could have a problem with the transom shift cable, ESA system, the bellcrank in the pivot housing and the shift rod height adjustment. The best thing you can do is find a good OMC mechanic, the second best thing is to look at the Stuart Hastings site on Cobra issues. His website tells you how to check the adjustment on the cable.
Here's what I do to mine each season: I remove the drive in the fall to check the bellows, gimble bearing and u-joints. For instructions on how to remove, see
http://www.crowleymarine.comlook in product support under OMC Cobra drives. They also have to proper procedure to fill the drive with oil, it MUST be followed or else the drive can be ruined!
Anyway once you remove it, you will see a linkage that comes out of the right side of the pivot housing, this is the shift linkage. You need to clean out the area around the bellcrank that is there and pack that area with OMC triple guard grease because if the gasket leaks just a bit, there will be crud in there that prevents the bellcrank from moving smoothly.
Also make sure the idle is low enough (500-600 in gear in the water) to allow easy shifting. When you shift to neutral you should feel the engine slow down, thats the ESA system allowing the gear to release. Your problem is not that, rather not going into gear. Does it grind or just not go in?
BTW don't let anyone tell you these drives are bad, the problem is that there are not a lot of mechanics that know how to set them up and some parts are getting to be hard to find, they were only made from 86-93. Mine is 20 years old, has been used in salt water at least 8 seasons, and shifts with 2 fingers, like it's supposed to.