2002 50 hp mercury outboard. Ongoing problem for 3 years. Engines cranks and idles good. Engines really runs good at 2000 rpms and up to and at top speed. Problem is: if left in neutral at idle for around three minutes, then shift into gear and start to throttle , motor usually stalls unless i push primer/choke on ignition switch. Every year has been serviced by mercury technicians and still have same problem off and on. Every year i I pay for having carbs rebuilt and fuel pump rebuilt. This year had gas tank replaced, all hoses and bulb replaced, carbs rebuilt, fuel pump rebuilt - guess what - same problem. What else could be causing this? motor also has water separator and fuel filter installed.

Hopefully your technicians have checked the engine set-up and have made sure the pick-up or idle timing is correct and the carburetor linkages are set correctly. I am guessing this is a 2-stroke engine and that the possibility of contaminated fuel has been ruled out. If idle timing is correct and your gas is perfectly clean. Your problem may be that the carburetors are adjusted to lean and may need the idle mixture to be richened up a little.

How this could cause your problem is if you slow down and then quickly accelerate again there is enough residual fuel in the crankcase that the engine will not stall. I am assuming that is what your engine does. After the engine has idled for three or more minutes the extra fuel is gone and because the idle mix on the carburetor is set to lean the engine dies on acceleration because the fuel is not being supplied fast enough. By you activating the primer you’re supplying the extra fuel.

Things you need to be aware of when the idle mixture on your engine is adjusting. If the engine is being adjusted with the engine simply running on a hose with muffs the back pressure on the exhaust will be incorrect and this could cause the mixture to be set incorrectly. If the engine is being run in a test tank make sure the water level on the outboard is similar to what it would be if the boat was in the water and that the water temperature of the test tank is close to the temperature of the water the boat is normally operated in both of these item affect idle mixture adjustments. The best way to adjust the carburetor is have the boat in the water and if possible and safe put the engine in gear.

Last thing make sure your idle speed is not set too low. Sometimes guys like to have low idle speeds for trolling. The idle speed adjustment is there to keep the engine running properly it is not a troll control. Hopefully this information is helpful.

Thanks for the reply. Tune up and sync was also done as I forgot to mention. Technician has had boat in water on three separate occassions this year and made carb adjustments. Problem always comes back. I'm almost convinced that it has always been something else ??? or just a bad carburetor that can't be adjusted or one that will not function properly even with a cleaning and a kit ???? Maybe replace the fuel pump rather than put a kit in it ??? Motor idles OK so I don't think the idle is too low. The outboard is a two stroke. Again, thanks for the reply.

I would have to agree with a setup issue, maybe it is time for a different mechanic to look at it, or have the dealership call for the tech rep to pay a visit.

I have taken the boat to several different Mercury dealers for repair/the problem is the problem always comes back/u can't just put the boat in the water and expect it to happen everytime...luckily right now it is acting up again and I had a tech who previously did service for the problem on board. He is somewhat bewildered / he could adjust the problem away but after running the boat for 15 or so minutes at different speeds the problem did return after a good long idle. The boat is at the shop and he says he will solve the issue. I'll post when I get it back.

have not water tested boat yet but a NEW carburetor was installed on the top cylinder / technician believes old carb loosing fuel flow up brass tube...this has been an expensive venture for a carburetor...if that fixes the problem. Will not post again if problem is solved...will know after weeknd.

I am a rank amateur at boat engine work. I'm a gov't worker who has been "given" this "opportunity" and will do my best. We have a 50 hp 2 stroke that idles fine on "monkey ears", haven't had it in water yet. When rpms are stretched out it develops a horrendous miss and sputter. Will try, SeaFoam in no-ethanol gas, and then work my way from there. Next is pull the carbs and rebuild them. Look forward to learning from y'all.