1987 Mariner 150 Running rough at idle, lean sneeze on initial startup, and stalling

Boat was not used for two years, and I finally launched it this spring and have been using it every weekend since fishing down the jersey shore. Few things I need answered. On initial startup I prime the bulb till firm, then crank motor over. Sometimes I can get it started fine, other times I get the lean sneeze, and need to work the bulb and keep cranking till it fires. Leaving slip under slight throttle the motor seems like its running rough, with noticeable vibrations you can both feel and see. Twice this year I was entering the channel, and go to throttle up and cant get past 3000rpm. This is with be putting the throttle handle at WOT. Then after about a minute or so the motor wakes up and goes back to normal. Not sure what that is all about. Lastly, when warmed up, when drifting for fluke, every time I restart the motor I have to choke it up to idle then have to literally slam shifter in gear and take off quick or the boat will die. Finally when returning to slip, the boat sometimes stalls out goin in and out of gear while docking. This is a general overview of what I ve been experiencing. Overall it hasn't stopped me from enjoying the boat. I do all the work myself, and I am eager to learn about this motor. I did the water pump, LU lube and new plugs this spring. Thinking maybe my carbs may need a rebuild. I have owned the boat for 7 years, and have done nothing to the carbs. Also never change the inline fuel filter or messed around with the fuel pump, if there is one:facepalm: Anyways sorry for long post, but I needed to get this out there. Any help would be great!

Re: 1987 Mariner 150 Running rough at idle, lean sneeze on initial startup, and stall

Do a spark gap test and rebuild the fuel pump first. Then maybe the carbs.

Re: 1987 Mariner 150 Running rough at idle, lean sneeze on initial startup, and stall

Ok thanks, how involved is the fuel pump rebuild? Also location on the motor?

Re: 1987 Mariner 150 Running rough at idle, lean sneeze on initial startup, and stall

It's a simple job to rebuild a fuel pump. It's like making a sandwich and bolting it to the motor. Following the fuel hose will take you to it.

Re: 1987 Mariner 150 Running rough at idle, lean sneeze on initial startup, and stall

When starting and after priming the bulb, do you choke the motor ? Check timing ...you may be having a sticking advance too. Sounds like carbs need a good cleaning ...not necessarily a rebuild. All gas filters clean ? Get a good manual for the motor. Getting a good spark ? Plugs correct ones and clean?

Re: 1987 Mariner 150 Running rough at idle, lean sneeze on initial startup, and stall

Yes I choke the motor while starting after I prime the bulb. Never touched the inline fuel filter since I bought the boat almost 7 years ago, I know I know !!! Will replace that this weekend. New plugs this spring went in. As far as carb cleaning should I unbolt and take a part and clean or just give them a nice carb clean bath while still bolted on the motor. I called my local merc parts dealer today. He asked me if I had the square fuel pump or old design? I m not sure, boat is down the shore won't be able to check till the weekend. Anybody wanna take a guess? Serial # for motor is B279500. He also mentioned that the only thing available is the fuel pump diaphragm and gaskets?? Is that the extent of a fuel pump rebuild?

Re: 1987 Mariner 150 Running rough at idle, lean sneeze on initial startup, and stall

a69nova said:

I called my local merc parts dealer today. He asked me if I had the square fuel pump or old design? I m not sure, boat is down the shore won't be able to check till the weekend. Anybody wanna take a guess? Serial # for motor is B279500. He also mentioned that the only thing available is the fuel pump diaphragm and gaskets?? Is that the extent of a fuel pump rebuild?

Click to expand...

Also included in the kit are small plastic disks for the valves.

Re: 1987 Mariner 150 Running rough at idle, lean sneeze on initial startup, and stall

There's no harm in repairing or replacing the fuel pump, but why not diagnose it first? It's easy to do... just prime the bulb when the motor starts acting up. If it makes it run normally, then the problem is in the fuel pump. By priming the bulb, you become your own fuel pump. Sounds like carbs to me, but the idea of it going in and out of gear by itself? That's a whole different story. You may be experiencing slippage either in the gear case or at the prop (prop slip).

Re: 1987 Mariner 150 Running rough at idle, lean sneeze on initial startup, and stall

Put a new in line fuel filter on it and soaked the carbs down with carb cleaner. Boat ran the same way today, started fine. Left the slip and only had part throttle for a few minutes even with the shifter at full throttle. Finally the boat accelerated and ran normal. It's almost like I had a throttle stop on the motor! I primed the bulb and it didn't clear it up. It feels like the motor has to build fuel pressure or maybe something is sticking in the carbs to not allow full throttle range. But after about 5minutes or so the motor runs great with no problems on the top end? I may finish the season out like this if I can't figure it out! And take the carbs odd over the winter and rebuild them. Kind of hard working on the motor in the slip.