recently got a boat and it would not into gear, figured it was where they was new cables and just wasnt ajusted right. so i came home and manually moved it on the motor, it kinda sorta locks in forward but if you give it a little push it will break over? Is this normal or should it turn my flywheel?

        its a late 80s black max 150 xr4

If the idle rpm's are too high it won't go into gear.

Could that be it?

i dont think so its where it should be 

Will it engage in either direction?

Yes, it should go in gear, but with a Mercury when you have it in forward, you should not be able to turn it in the forward direction without the flywheel turning also, but you can make the prop turn in the reverse direction and it will make a clicking sound.  This is to prevent deceleration knock the OMC/BRP motors have because they don't free wheel in reverse.. 

 

Also, if it's not locking in forward, take the cable off the motor and try manually shifting it.  It's very possible the cable is not adjusted properly.  If taking it off lets it lock in gear, adjust the cable by turning that piece on the end that goes into the motor bracket so it moves it a little further in the direction it needs to go.

i did it manually and it wont fo in it just locks but will break over. it will go in reverse though

Still won't go even with the cable disconnected as bkeith suggested? Make sure you're slowly turning the flywheel or prop as you're trying to shift. Helps it engage in the LU.

If it still doesn't work I would think you've isolated the problem at least. Then you'll have to go from there.

i had a similar problem once, and the cause was the lower unit barely had any oil.... 

You make it sound like the prop is locking and one way it's not. If that is the case, then you are backwards on the direction the prop is suppose to turn. If you have it shifted in forward, you are suppose to be able to turn the prop on reverse, there is no way you can keep it from it, that's the way Mercury designed it.

DO NOT try to shift the boat into gear while the motor is not running, you can cause damage.  If you must shift the motor while not running you MUST have someone turning the prop by hand while you attempt to shift.