5.0 MPI wont start half the time, runs great, please help!

[Dom33]

2007 mercruiser 5.0 MPI with 420 hours. When starting get a clunk and nothing, after several tries get a weak start but then motor runs great. Put in two fresh batteries, alternator seems to be fine. In the research I've done thinking distributor cap, or other starter component, or possibly a short? We had a full tune at the beginning of last season, plugs, distributor cap, etc. This happened on first trip of this season after having new exhaust installed, full outdrive service, and winterized at local mercruiser marine shop in the fall. This never happened before. Any advice greatly appreciated.

 

[alldodge]

Remove the battery cables at both ends, clean to shinny metal and reinstall. Don't forget the ground cable on the block.

When cables are removed, see if you can look under the insulation jacket

If after all clean and tight and problem continues, may need a new starter

 

[Dom33]

Thanks so much for the help. I cleaned the terminals at the batteries and at the starter with wire brush, found a lot of corrosion at the terminal on the starter. Now starts up like a charm. Great help!