50hp Merc Classic stalls when giving throttle

[nubutlernin]

Hey all, hope you can help. I bought an older boat last year from a guy who told me he had done lots of work to the boat. Looking at it, it seemed so. One of the things he said he had done was to rebuild the carb. The first few times I used it everything was good, but the third time I started having a problem. When it is cold, it starts easy and runs beautiful, slow orhigh speeds. Once running for about 5 mins if I want to run very low speed for trolling it sounds like rpm's are much lower than at first start, then it will slow more, then stall. To start it, I need to press the choke and have the "neutral throttle lever" up about half way. When I put it in forward and try to speed up, it will stall. It will do this usually at least 5 times before it finally catched and I can throttle up. Once I slow down again to try trolling or even go into my slip, it will stall out within 20 seconds. I used seafoam for the carb, and in the gas this year and put in brand new plugs. When I had done that, I ran at my house with muffs for 30 mins and never stalled out. Any suggestions where else I can start looking?

 

[mr 88]

Re: 50hp Merc Classic stalls when giving throttle

Running on muffs at the house is not the same as in the water. There is no back pressure as the exhaust is not under water so it will idle higher and shift with no problem, also there is no load on the prop.Have you adjusted the idle jet screw ? If that is turned in too much acceleration can be iffy to none. 1 1/2 out as a base setting,then you may have to turn it out a 1/8 of a inch,then test and repeat. It can be touchy finding a happy medium between a good idle and acceleration do to the design of the carb.

 

[Toddboat]

Re: 50hp Merc Classic stalls when giving throttle

Running on muffs at the house is not the same as in the water. There is no back pressure as the exhaust is not under water.

Mr88, I always wonder why a motor will run well in the driveway and then not run in the water. You've given a reasonable explanation, but it still leaves some unanswered questions... motors don't exhaust through the prop at idle, in reverse, and sometimes not even at low speed. They exhaust above the water in those instances, and only exhaust under water once the boat is underway and there is a vortex created behind the prop for the exhaust to escape into.
However, using your explanation, would the motor theoretically idle the same in a barrel of water in the driveway as it would in the water?

 

[mr 88]

Re: 50hp Merc Classic stalls when giving throttle

Why do you think they do not exhaust through the prop at idle etc. There is no check valve in this system,it all dumps through the prop.It may idle the same in a barrel of water as long as the barrel is big enough so the water is not always being pushed out as it's running. Now when you try and set your jets, the complete resistance of not moving as you put it in gear is not the same as being in a boat and putting it in gear.

 

[GA_Boater]

Re: 50hp Merc Classic stalls when giving throttle

Mr88, I always wonder why a motor will run well in the driveway and then not run in the water. You've given a reasonable explanation, but it still leaves some unanswered questions... motors don't exhaust through the prop at idle, in reverse, and sometimes not even at low speed. They exhaust above the water in those instances, and only exhaust under water once the boat is underway and there is a vortex created behind the prop for the exhaust to escape into.
However, using your explanation, would the motor theoretically idle the same in a barrel of water in the driveway as it would in the water?

Partially right, except the final adjustment should be in water and in gear so the mixture is adjusted for load. Another thing that happens in a barrel is the water is heated by the exhaust and cooling water into the barrel. So the possibility exists for running the motor warmer than when it's on actually on the water. Something to watch for, even if a hose is keeping the barrel full.

As far as the exhaust, just about all motors have an exhaust relief so all the exhaust isn't forced through the under water exhaust. Other wise starting could be difficult. But most the exhaust still goes through the under water outlet. My Merc in a barrel blows a water mist and exhaust out of the relief when is running, idle, forward and reverse. But during all those times the exhaust through the prop is like an elephant with gas, same when it's on the water.

 

[nubutlernin]

Re: 50hp Merc Classic stalls when giving throttle

Thanks guys, I have been away for a bit....damn emergency surgery, but all is good.
I will play with idle screw and let you know. Appreciate it.

 

[nubutlernin]

Re: 50hp Merc Classic stalls when giving throttle

Well, adjusting the screw helped a lot....it was almost turned all the way in. Played with it a bit and had it running at low speeds quite nicely for a while. Tried trolling with it and it was good for almost 5 minutes, then it idled down and stalled.
I am certainly a novice (thats why the name..nubutlernin) when it comes to adjusting the screws, and I noticed there are other ones that are accessible through "screw-holes" at the front of the motor. Will adjusting these help at all?

Oh and I am guessing my starter needs replacing....brand new battery, only clicks when I turn the key. Had someone passing by tap the starter while I turned the key and it fired up. I was out in the boat by myself for the day, so I couldnt reach the starter to hit it when I needed to start it, so I had to use a pull rope.....not easy to do on these puppies, especially two weeks after major stomach surgery, but I managed! The question....is it easy to replace the starter on these. It doesn't look that complicated. Thanks for all the help!