1976 mercury 850 idle problems

[Ifkyk]

I bought this motor last year the motor had sat for at least 15 years said the guy I bought it from the dude that had it before him let it sit up for almost 8 years so the motor had sat up for 23 years with that being said wires were completely shot bought new switch box trigger and rectifier and was able to save the stator cleaned carbs new plugs and a little starting fluid busted off second crank got it all mounted on the boat and runs good out of water and in the water but after I open it up over 1/4 throttle and back off of it will not idle I can put it in neutral and give it half throttle and it struggles to fire back up and even when it does it runs rough run it 1/4 throttle for a few minutes and back to idle normal I don’t have a temp gauge set on it but it’s steady peeing always at a good stream water coming out isn’t hotter than when it is running normal I’ve rebuilt fuel pump and carbs new fuel new water impeller also does anyone know how the rectifier is sopposed to be wired up it’s not charging and after I rewired it I’m not sure if I wired it back right

sorry for the lengthy post but I’m lost thanks in advance!!

 

[Chris1956]

OK, easy stuff first. Rectifier has 4 wire connection posts. Original Mercury rectifier had the -DC post connected to the motor frame ground via the mounting bolt. Aftermarket full wave rectifiers must have the -DC post grounded to the motor frame.

The 2 AC posts get yellow wires from stator. The +DC post gets a red wire that runs to the starter solenoid secondary and connects to the main battery positive.

Temperature gauge is useless as motor has no thermostat. New impeller, wearplate and 2 gaskets are all the cooling system maintenance that is required.
Your running issue sounds serious. However, setting the carbs is a bit unique for those year Mercs. Initial setting is 1-1/2 turns open. Float heights need to be set properly. Invert carb covers and bend lower lever until top lever is parallel to carb cover. Floats must be hard white plastic, with little springs on their tops. Replace them if they are the foam type.

Final carb adjustment must be on the water, in gear, motor warm. The carbs must be richened enough to allow smooth acceleration and reasonable idle. The initial setting just allow idle and usually causes stumble upon acceleration.

Timing spec for idle pickup is 0-9* ATDC. Max spark advance is 21*BTDC. Have you linked and synched it?

Check you spark plug color after running in water for a while. If any plugs are real clean and different from others you may have water infiltration.

You probably need an OEM service manual.

 

[Kailofsouls]

Have you checked the fuel lines? Mine were shot on my 73 1150 they may look ok on outside but inside they could be falling apart. 3/8 from tank to motor 1/4 from pumps to carb was my sizes. I just bought fuel line by the foot at an auto parts store. If you work at the brass fittings you can pull them apart. Just hose clamp the new lines on. Otherwise it's 100-140 for the lines online. Cost me bout 25 bucks.