Thread: Need Help on 4 stroke 15 hp 2000 Mercury

put in a new Mercury fuel line and primer, so that is not the problem. tell me more about the sensors and the fuel pump.

Failing fuel pump will run normally for a short period of time while the carb is full of fuel that has been manually primed. As the fuel level drops in the carb, symptoms appear. I don't think that's the issue based upon your description. The electronics on the little four strokes monitor both oil pressure and temperature. It also has a way of detecting whether the motor is under load. If you will notice, it will go into limp mode (surging) pretty quick on the water hose. (No load). Same goes for attempts to high rev in neutral. Your description of the problem sounds like an engine in limp mode. Carb or fuel problems will at some point kill the engine due to too lean or too rich of a fuel supply. I'm not clear on if this is occurring on the lake in forward gear or on the muffs. Also, knowing the year model might be of some help. The earlier ones had yamaha powerheads while the ones made in the last ten years are tohatsu made.

Originally Posted by sliderman

Failing fuel pump will run normally for a short period of time while the carb is full of fuel that has been manually primed. As the fuel level drops in the carb, symptoms appear. I don't think that's the issue based upon your description. The electronics on the little four strokes monitor both oil pressure and temperature. It also has a way of detecting whether the motor is under load. If you will notice, it will go into limp mode (surging) pretty quick on the water hose. (No load). Same goes for attempts to high rev in neutral. Your description of the problem sounds like an engine in limp mode. Carb or fuel problems will at some point kill the engine due to too lean or too rich of a fuel supply. I'm not clear on if this is occurring on the lake in forward gear or on the muffs. Also, knowing the year model might be of some help. The earlier ones had yamaha powerheads while the ones made in the last ten years are tohatsu made.

2000 2 cylinder 4 stroke electric start. When I am on the lake, it starts immediately, idles fine (although a bit too fast in my opinion) and does just fine when I put it in forward or reverse. does not sputter or try to stall when engaging the gear.

Will purr along at about 1/8 throttle all day long, but starts sputtering immediately if I attempt anymore throttle than about 1/8. It doesn't die, it just sputters and keeps going.

At home, I put it in a large garbage can filled with water, not muffs. It pees fine and the water remains cool, even after several minutes of idling while I adjust the idle speed screw or make other adjustments. It will start and idle just fine (although too fast) if I set the idle screw about a full turn and 1/2 after it first touches the part that the throttle linkage connects to to control the speed. If I try to reduce the idle speed down less than this full turn and 1/2, it then just dies immediately.

also, if I try to increase the throttle speed past about 1/8 or so while in the water pail (in neutral or forward), it sputters just like if on the lake, but does not die or get additional power.

thanks for any additional suggestions. I can go fishing at the lake I generally fish (Lake Conway in Arkansas) and get around slowly, but the sputtering and lack of speed/power is extremely annoying and probably not good for the engine.

Paul

Originally Posted by Erin Brewer

Check your fuel lines and prime pump. I had a 15 4 stroke and the lining of the fuel line was coming apart clogging the fuel system. Just pull the line connection off of the side that connects to the engine and check it out. Or just replace the line and bulb.

Exactly what he said, I had the same issue. I would take the carb apart, clean it and shortly after had engine problems again. The fuel line was coming apart, clogging the carb back up.

Ok.. That gives a much better understanding of what is happening and the conditions it happens under. I more strongly suspect the engine is in limp mode at this point but that is yet to be determined. A couple of questions first as I suspect this motor has more than one issue.
1) The 1 1/2 turns on the idle speed screw after contact. Tell me why you do this. Also, is there still a brass colored plug on the carb?
2) When the carb is empty and you prime the bulb, does the line become firm near instantly?
3) With the spark plugs removed, is the color of the electrodes a sooty black or some degree of a tan color?

Here's what I'm thinking at this point. The high idle is required to offset an incorrect idle mix (common problem created by two different problems). Also, the o-ring bowl gasket is very prone to leak gas in the area where the incoming fuel is suppose to go from the inlet (bowl) to the body. Where it is then suppose to be metered by the needle. When it leaks, it by-passes the needle and creates a very rich running condition. With that said, I'm trying to determine if the idle mix is too lean or too rich.

whoa, what a dumb butt on my part. looked at the pictures of the disassembled carb today. I had taken a piece that went on one side of the carb and put it back on the other side. the choke did not fit because of this error. once I moved the part to the other side, was able to move the idle speed to a quiet whisper, but steady. it shifts and now revs.

when in doubt, read the instructions. my bad!!! thanks for all the help guys. playing golf tomorrow, but will hit the water on Friday and get back to you with a report.

paul

Taking pictures before and during dis-assembly are worth their weight in gold..

Glad you got it fixed to go