Boat engine spares… case studies.

I purchased a boat but bought a secondhand outboard motor from a different place. The motor has been working fine but when we bought it, the previous owner said he usually replaces the impeller every year but had not got around to it this year. Having never owned a boat before, we decided to wait to do the impeller until we actually used the boat and knew it worked OK.

We eventually took it out the other night and the motor acted like it was missing and kind of revving up a bit. We changed the spark plugs and then took it back out. Although it actually sounds better now, no water was coming out of the holes. We have ordered a new impeller.

Any marine dealer can get you engine parts. You can get information and source suppliers online from sites such as www.boatpartsdatabase.com.  Check the wear plate and cup for any grooves near the driveshaft, if so, replace the parts. If it isn't the impeller, you could also take it to a good service shop and have them go over the motor, using a water pressure gauge. Have them do a complete check of the motor. Since the motor might be as much as 40 years old (quite feasible life expectancy for many outboard engines) it is best to consult an expert. Some things are possible for a DIYer with some good tools, many things aren't.

On the bigger yachts, inboard engines might start cutting out and the motor start jerking, unable to go over 3000 RPMs (sometimes speeding up like it wants to take off, but then start restricting itself again), running fine if kept under 2000 or 1500 RPMs, shuddering at times. If you make it back to the dock pull the caps to the plugs off one at a time… check for a spark. The plugs would spark fine fewer than 2000 RPMs, but would start missing on all of them if we got it over 2000. I have spent more time fixing this stupid thing than I have actually using it.

First of all, I couldn't recommend used ignition parts, you don't know how long they will last, have no warranty and may be on their last legs. You could have a bad stator. Mercury has put out service bulletins on their stators. What is happening is you have two sets of charge coils and one set of alternator coils on your stator.

The stator is the series of coils under your flywheel. One set is the low speed, and the other the high speed. The high speed coils can burn out. You will need to replace the entire stator. You will need special tools to remove the flywheel.