merc 650 wont stay running

so im new to this forum and im not sure if any one can help me but i reasantly bought a 1975 mark twain runabout with a merc 650 3 cylinder it was running fine for a while than i pulled it out of the water. after about 1 month i went to fire the motor,so i hooked up the hose for the water and when i went to start the motor it would not start unless the throttle was at half and when i would try to idle down the motor would die. if any one can give me some tips on what might be the problem or how to diagnose it i would be much ablidged. thank you

Re: merc 650 wont stay running

That motor is junk . . . I'll take it off your hands for $10.

Seriously though, it sounds like the carb is gunked up or has fuel line deposits in it, or something like that. Maybe an idle breather is clogged since it is having trouble staying alive at lower throttle settings. I would do a thorough cleaning of the carburetor by removing it and running harsh solvents through all areas of it. See how things go once it is all back together. Maybe verify that the fuel lines from the tank and leading into the carb are in good shape.

Re: merc 650 wont stay running

Welcome to iboats.

Yup, you have a carb problem. Lifting the throttle half way bypasses the idle circuit which I suspect is clogged.

You will have to clean the carbs as stated above and I will add that you need to go deep into the carbs by removing everything.

Get a proper manual and do not be intimidated by the procedure to do a proper cleaning.

Re: merc 650 wont stay running

You have dual carbs on your motor and they're connected. Be sure to be careful when removing the carbs so that you don't break any of the parts connnecting them. You'll have to remove the starter, don't forget to disconnect the battery FIRST!!
Like the others, I'll bet your carbs are dirty, and when you remove the fuel bowls there will be all kinds of crud in them. Even if there's not, the low speed jets could still be and probably are clogged. Go ahead and replace all fuel lines, or this problem will likely reoccur as varnish breaks loose from the lining of the fuel lines and heads for the carbs. I own 2 of those merc 650's. If you ever go fishing and for no obvious reason it will turn over fine but never make any attept to crank, bring a flathead screwdriver to disconnect the power wire to the cd box and the black wire at the bottom. Somehow or the other it resets the cd box and it will fire again. Both of my 650's have required this for no apparent reason, but it ran perfectly thereafter.
Good luck with yours,
JBJ