Before I replaced the block/head dowels on my Mercruiser 888, it started easily and ran well. I have rebuilt more than a dozen car engines and nothing was out of the ordinary with job. Now that the rebuild is complete, I can not get it to run. It turns over strong but doesn't catch. The only thing that I can think of is the timing because the distributor had to come out. I did mark it and attempted to replace it in the same position. Can any body help me?