I just took delivery of a 2002 boat with 25hp Mercury two cylinder, four stroke, which is sourced by Tohatsu I believe. I tested the engine on a flush muff about a month ago and it started and ran fine, although idled a bit fast. Meanwhile I've been waiting for the guy to get the title straightened out. The boat and motor are as new with maybe a couple hours max on the motor. I bring the boat home and it cranks a couple revolutions and then stops. I pull the plugs and it looks like it may have hydrolocked in the upper cylinder with fuel. The 100+ degree temps have pressurized the plastic fuel tank with the vent closed so I assume the carb and cylinder have been flooded with fuel. The battery is fully charged. I put the lanyard switch in the off position with the plugs out and crank if for 10-15 seconds. It sounds normal while cranking with the plugs out. I reinstall new plugs and it cranks a revolution or two and then stops, like something is restricting crank rotation. It does the same thing with the lanyard in run or off position. I don't have a compression gauge yet to fit the small plug thread but that will be my next step. Any known problems here, or any thing I am missing, or any suggestions? Vernon
With the kill switch activated and spark plugs in attempt to manually rotate the flywheel to feel if anything is binding. Don't force it. If you don't feel anything preventing rotation then the problem lies in the starter or starter circuit. Sounds like the starter is not getting enough amperage from the battery. Batteries get old, wires corrode and develop resistance. Both can prevent the starter from rotating at speed.
Initially it appeared to have excess fuel in the upper cylinder, but that is cleared out now. One year old marine battery, fully charged, with engine running car battery in series, still won't crank more than a revolution or two. All electrical connections are tight and corrosion free. Engine appears new with maybe 3-4 hours max, 2002 25hp four stroker. I can pull the engine thru with the rope start and plugs in OK. I'm guessing starter may be dragging?? Or?? Any known components suspect on these engines? Vernon
Sounds like you need to rebuild/replace the starter. If amperage is there and solenoid is functioning properly then there's something preventing current flow in that 10 year old starter.
Thanks.....sounds like I ought to get a shop manual and see if there are any tests for starter and/or solenoid function while on the motor. Any tests you think of? Vernon
Great, will check it out. I guess an auto electric shop could do a bench test on the starter maybe? Vernon
