having problems with 1990 115hp mercury

[dgonzales811]

I'm a 1st time boat owner. I just bought a 1991 alumaweld bass boat with a 115hp mercury. The motor is a 1990 model. The guy I bought it from said he had the carbs rebuilt last year and does all the yearly maintnence but hasnt taken the boat out for almost a year. I've taken the boat out 3 times and every time I've had the same problems. When I first start the boat I have to crank it about 4 or 5 times for the engine to start and stay on. Then after letting it warm up for about 5 min. I drop the idle down and it idles really rough fluctuating between 400 to 550 rpm acting like it wants to die and sometimes actually dieing. Another problem occurs when I put it in gear. When I put the engine in gear if i dont give it about half throtle and drop back the boat will just die even if the motor is warm. What I've been doing is giving it a little choke so it gets up to about 600 rpm and then dropping it into gear. Once it finally gets going it works like a charm. I just feel like maybe I'm having to to too much work for this motor to run properly. I assumed I would just start it, put it in gear, and go. What could be the cause of these problems and how can they be fixed?

 

[WillyBWright]

Re: having problems with 1990 115hp mercury

Welcome to iboats and welcome to the world of manual choking.<br /><br />That definately isn't a turn-key motor and there's nothing anybody can do to change that. There's only one way to start it fairly easily...<br /><br />Pump the Primer Bulb on the fuel line until it's firm.<br />Make certain the Emergency Shut-off switch is on Run and the shift is in Neutral.<br />Push the key in to operate the Primer (choke) and turn the key.<br /><br />There are a couple things that are Real important.<br />Don't give it any throttle until it starts.<br />There is no Automatic Choke feature. Push the key and it chokes, let off and it doesn't.<br />They take a good minute or two to warm up in normal conditions. In cold weather and/or water it could take a few minutes more.<br /><br />Another thing you should be aware of is that the motor runs on 2 cylinders at idle and above half throttle it runs on all 4. Between about 1800 and 2200rpms it will have a difficult time deciding whether to run on 2, 3, or 4 cylinders, so avoid that range. It's a quirk of the design that has caused a lot of headaches to those that are unaware of it. There's nothing wrong with the motor. The 4-cylinder 100s, 115s, and 125s all do it.<br /><br />Other than that, it sounds like the only two mixture adjusting screws you have need to be opened a bit. I'll guess 1/4 turn. They're on the side of the tops of the top two carbs on the port side. There's an accelerator pump on there as well that could be out of adjustment, but I'd fatten up the upper two carbs first and see if that cures the quitting problem. Or the idle speed needs to be bunped up. It should idle around 650 in gear. I believe the idle speed adjustment is a small screw on one of the major arms. It should be marked. It adjusts timing, not the throttle like most every other motor on the planet.

 

[dgonzales811]

Re: having problems with 1990 115hp mercury

When you say push the key in to operate the primer choke, should I hold the key in while I crank or just push it in a couple of times and then crank? Another question is once I've already run the boat to the spot where I'm going to fish, when I am ready to move again should I have to repeat the same procedure or should it be easier since the motor has already been warmed and run? Also, in your opinion, is this a good motor or a piece of junk?

 

[Laddies]

Re: having problems with 1990 115hp mercury

When the engine is cold advance the throttle lever and hold the primer till the engine starts some enguines after starting require telegraphing the primer after startup, when warm the engine should start without primeing but if set lean, it may require priming---Bob

 

[dgonzales811]

Re: having problems with 1990 115hp mercury

what should the motor idle at when it is in neutral?