hard starting and low power on 1999 Johnson 15hp

I bought an almost brand new 1999 Johnson 15hp. It was supposed to have less than 10hrs on it and well taken care of. The engine looked brand new. It worked well for the first trip but it overheated on the second when the water pump quit. It started to smoke and smell like burnt rubber but I was pretty far offshore so I needed to get back so I just kept going until it quit. When it quit, I paddled for a bit then fired it back up and got back to the dock.<br /><br />I pulled the lower unit and the impeller looks gone so have ordered a new water pump kit.<br /><br />Is there anything I need to check since the motor overheated and quit?<br /><br />I checked the compression afterwards and it was 105# and 110#. The plugs looked good, slight brown color but not black or oily.<br /><br />Before it overheated, it seemed pretty hard starting from cold. Maybe about 5-6 pulls to fire it up. Should I change the plugs and would this correct it? <br /><br />Also the power didn't seem all there. I had a small 10', 130# RIB boat and it wouldn't plane with about 700#s loaded in it (2 people + gear). It would plane with 400#s (2 people + less gear) but seemed to take quite a while and only in flat water. <br /><br />The manual recommends ql82c. Can I replace it with L77JC4 and get more power out of the thing and easier starts? I almost never troll and am usually at full open throttle. <br /><br />Is it possible that I am losing 1 cylinder? It sounds really smooth however. Can I check this by pulling the boot off one of the plugs while it is running?<br /><br />Thanks for any suggestions.

Re: hard starting and low power on 1999 Johnson 15hp

Well well well.<br />First of all, you will never get more power, by changing to another type og plug.<br />Use the plug, there is recommended in your manual.<br />Since your motor sounds smooth (when running), Im sure you are not loosing 1 cyl.<br />A new motor there is hard to start, missing power and compression "only" at 105 and 110, looks like more or less damage on your pistons, pistonrings or cyl.wall.

Re: hard starting and low power on 1999 Johnson 15hp

Pulling the spark plug wire off of a running engine is a good way to check for a dropped cyl.

Re: hard starting and low power on 1999 Johnson 15hp

If it overheated, one of the coils might have melted and is shorting to ground. Look at the coils for melting atleast. Duke3 spoke of piston damage. Might be right. Pull head off to see. Gasket less than 20 bucks.