115hp Mercury outboard 2cycle, loading up at idle

[Brice Zachow]

I have a 1999 Mercury 2cycle outboard motor with 4 carburators. This motor runs great as long as it is perfectly level. If the motor is trimmed either up or down it starts loading up and running rough. If I run the motor at planeing speeds, and then return to wakeless speed, it will run rough even with the motor trimmed perfectly level for a few minutes, (like the choke was pulled on a warm engine) until it apparently burns off the excess gas, and then it runs great again as long as the motor trim is kept level. I pulled the carburators and checked the float levels, and they were all at the specified 7/16" that the manual recomended. Instead of a choke, this engine used a system that floods raw gas into the crankcase when you push in on the key, but it seems to be working perfectly. Any suggestions would be greatly appreciated.

 

[alana]

Re: 115hp Mercury outboard 2cycle, loading up at idle

is one or more of the needle valves sticking. are the floats shutting the fuel off. i once found a carb float that had a hole in it, and had filled with fuel, it sunk in the bowl and did not shut needle valve. also do the floats move freely

 

[yamamarinetech40]

Re: 115hp Mercury outboard 2cycle, loading up at idle

Brice, I'm not a Merc specialist, but if you have 'pulse' type fuel pumps with rubber diaphragms, if the diaphragm gets a hole in it, not only will it pump gas on the 'pulse' of positive crankcase pressure, but will 'suck' gas into the crankcase, also, especially when you chop throttle.....check it

 

[JUSTINTIME]

Re: 115hp Mercury outboard 2cycle, loading up at idle

sounds like floats to me not the fuel pumps

 

[roger3645]

Re: 115hp Mercury outboard 2cycle, loading up at idle

Are you getting a firm priming bulb when you squeez it? If not, then it's most likely a needle valve not closing.

 

[Brice Zachow]

Re: 115hp Mercury outboard 2cycle, loading up at idle

is one or more of the needle valves sticking. are the floats shutting the fuel off. i once found a carb float that had a hole in it, and had filled with fuel, it sunk in the bowl and did not shut needle valve. also do the floats move freely

 

[Brice Zachow]

Re: 115hp Mercury outboard 2cycle, loading up at idle

I cleaned all of the needles, because they did have a black film on them, I checked the floats for fuel in them and they all seem fine. I have firm primer bulb, and don't think motor trim would cause the problem if it were the fuel pump. If nobody has any ideas besides the carburator though, I guess I better focus on them, and kit them rather than just cleaning them. Thanks for the responses

 

[JUSTINTIME]

Re: 115hp Mercury outboard 2cycle, loading up at idle

u need to runn all the fuel test first
like vacuum and pressure before and after the pump

then rebuild carbs do sync and link
look at plugs

 

[alana]

Re: 115hp Mercury outboard 2cycle, loading up at idle

wayout thought. could the trim wireing be making the press key to choke wire live

 

[Brice Zachow]

Re: 115hp Mercury outboard 2cycle, loading up at idle

wayout thought. could the trim wireing be making the press key to choke wire live

 

[Brice Zachow]

Re: 115hp Mercury outboard 2cycle, loading up at idle

I had a buddy trim the motor while I watched and listened to the solenoid valve that responds to the push key choke, and it was not affected, and neither was the accelerator pump. I'll follow through with the fuel tests and rebuild the carbs if neccessary, but can't get to it for a couple of day's. Thanks