I have a 98' Mercury 15 HP tiller that I purchased with my boat back in the spring. It has ran like a top all summer until last night. Me and my Dad were out on the river catfishing and I pulled the rope to start it for the ride back to the dock and it started right up but then immediately stalled. Finally after about 15 pulls it cranked on and I just hit the throttle because I didnt want to be caught in the outgoing Delaware river tide heading away from the ramp. It ran fine till I got back to the dock and as soon as I killed the throttle it stalled once again. This time I was able to start it after 4 or 5 pulls but once again as soon as I motored onto the trailer it stalled again. Any ideas? I am definately oing to get it tuned up and a waterpump/impeller replacement before next season but what could the issue be? Any advice or idea would be greatly appreciated. This is my first boat/motor and I am totally clueless.

Some other factors to note, it was the first time the boat was used in about three and a half weeks. I had 3/4 tank (roughtly 4 gallons) that I put in a month or so back with a 50/1 oil to gas ratio as per motor reccomendations.

The usual suspect would be. Plugs, filters, carb, fuel lines. I'm not sure about mercury's but, I would check for a fuel filter and replace it if it had one. If your motor is pumping water I don't know why you would service the impeller. It wouln't hurt to change the plugs and carry an extra set with a wrench for emergencies. I wouldhave somebody clean the carbs also. If you are handy with a wrench get a manual you can get lots of good info in there.

I have a 88Merc 15HP . Mine has done just what your has.

1. is you vent cap open on your tank?

2. replace the plugs? even if they look good change them

After some time of trying many different brands of plugs. I have found out that NKG work best on mine. With Champion next. Autolite, AC delco seem to foul out fast, and split fires were a no go. Ran really bad.

3. get some fuel conditioner. I like OMC 4+2 (or 2+4, can't remember) the best. Its a fuel stabilizer/conditioner. put that in you tank with some fresh high test gas and it might help clean it out some.

Dont forget the fuel pump.  In my case it was cheaper than a carb clean and it ended up being the fix.

Always start with the cheapest and easiest fix then move up the line in order of cheapness.