Dinghy motor sometimes dies randomly, other times speeds up and slows down

[TheNomadicAspie]

I could be missing something really basic but after reading the manual for my Mercury outboard motor I'm stuck so hope you guys don't mind me asking this.

I've only had my boat/dinghy for a few days now and my outboard motor seems to do what it wants. I make sure it's in neutral, pull the choke out, make sure the throttle is in the middle position, pull the starter cord, shift it into drive, then move the throttle counter clockwise.

There's a couple things I can't figure out. The manual says to push the choke in halfway after the motor seems up, then push it in the rest of the way.

I don't know how long it takes to warm up the motor so I've tried different things. If I leave the choke out for several minutes, the motor starts to sputter and die.

If I push it in halfway after it starts to sputter, it runs steady for a minute or so then dies.

Usually it starts up again right away then dies, and sometimes doesn't start at all. I know that's because I'm flooding the engine, but I basically can only get from point A to point B by doing this repeatedly which I'm sure isn't good for the engine.

To fix it, I've tried draining the carb which sometimes will help. I've also taken the carb apart and ran carb cleaner through the jets. Though when I try to unscrew the long screw/jet that runs through the carb, it's stuck and I actually started to strip the screw trying to remove if so I just left it on.

Could that be the issue? I want to try to fix it myself so I can learn and gain the experience, but does this sound like something I would need to pay someone to repair? Or am I just operating it incorrectly?

What should I be trying? Ive read my repair manual but I'm not sure what the problem is so I don't know what to try and fix. Specifically I don't know if it's user error or a mechanical issue.

[tkeithlu]

The simplist answer that comes to mind is that you may have water in your gas. That can produce weird irregular starts and stops.

On the choke side: As the cylinder and piston head heat up, the fuel fed in vaporizes more. The amount of fuel that produces the right mixture of air and vapor for combustion drops. Just listen to it. Adjust the choke for good throttle response, because goosing the gas cools the whole system, making a tiny bit more choke and a richer mixture necessary.

I recommend that you clean out the tank and drain everything, put in new gas, and try again. It certainly sounds like your engine is trying to run. If that fails, then let's talk about next srteps.

[Jammer]

There is a certain amount of guesswork involved since we don't know the model, year, or service history of the motor.


Typically the problems you describe are caused by blockage of jets and passages in the carb. To remove the jet, use exactly the right size screwdriver, grinding down a larger one if necessary to get an exact fit. Push down with a good deal of pressure while turning. You can also use gentle heat on the housing or try soaking the carb in solvent for a few weeks.


If the jet is a real mess you're probably better off with a new carb. In most cases they aren't particularly expensive.


Full choke should be necessary only for a few seconds, maybe more in extremely cold weather, and half choke shouldn't be necessary for more than half a minute or so. If the engine dies then you have a clogged or misadjusted low speed circuit.


Fuel pump problems, fuel line and fuel filter problems, and (if applicable) problems with the fittings and pickup strainer in the external tank, can also lead to fuel starvation shortly after starting which leads to similar symptoms.

[flyingfin]

Need to know year and type carb. What is still called a choke on newer engines is just an extra jet that enrichens the fuel ratio when first starting. Let the engine warm up (time to warm up is dependent upon ambient air temperature). Once the engine is warmed up, turning off the "choke" just closes the extra jet and you are now running the proper fuel/sir mixture.

[Craig Cape Town]

I had similar issues with my Mercury 3.5hp . I tried cleaning out the gas tank and the fuel lines, also stripped and cleaned the carb.
The adjustment screw , which comes fixed, had been tampered with and I could not get it to idle properly. Eventually I replaced the carb. with a Tohatsu carb. (same as mercury but cheaper ). That solved the problem, but I still however failed to identify the cause.
I'm be interested to hear what the cause of your problem is.
Good luck.

[clownfishsydney]

2 or 4 stroke? HP? All different.

[Geitz]

I had the same problem with my Mercury 4hp 2 stroke. There was a tiny piece of dirt in the jet. It wouldn't run without constant feathering of the choke.