What size engine is it ? Most likely it's not hydrolock, it's, as stated, the elec. starter/battery combo is insufficient to turn over the engine. I have a new Tower Hobbies .75 engine and a Tower's regular-duty elec starter. It couldn't turn the engine over at all when it was brand new. It can do so now if I give it a running start as suggested above. I disagree with the above post on this practice being dangerous. It's not dangerous in the least, you jam the starter onto the spinner while it's "at speed" and the centrifical force of the spinning motor allows it to turn the engine. The starter is spinning slow so it's not dangerous and it's grippy enough to never slip off. Works for me.