timing question..

[shaunster]

just had my motor rebuilt..

installed the motor..

and it started...

went to take the boat down to the lake..just before I went down.. I tried starting it again..it wouldn't start...

I have Spark, And gas..When I did the timing I put it where I had it on my old motor..and again like I said it started the first time..I didn't have a timing wheel..

So..does it have to be right on the mark....? and why did it start the first time..??

Thanks !!