76 Merc850 set-up & tuning

[rogman143]

Hey guys, been reading for long time, first post. I have a '76 merc 850 thunderbolt on a '71 14ft Glastron. Its a fixer-upper to say the least. Couldn't pass it up for the price.
I just rebuilt both carbs and the fuel pump, new plugs, and new cables. I soaked all the parts overnight, blew all the ports out, sealed the expansion plugs. I set the floats like the diagram said, ran new fuel lines from tank all the way to the carbs. Runs like a beast on the muffs, very crisp. I put it in the lake and it doesn't want to start or idle.
I finally got it started with the cowl off, and out of the hole, top end screams. I ran it around to warm it up, but it still won't idle smoothly. Replacing the cowl seems to cut it back quiet a bit. It's very hard to start, and idle is up and down. I'm out of ideas, and can't seem to find anyone who knows how to tune it.
Anyone with suggestions?

 

[Barnacle_Bill]

Re: 76 Merc850 set-up & tuning

Do a link & sync according to your manual.

 

[Moody Blue]

Re: 76 Merc850 set-up & tuning

Lots of the same problems being posted in the forum right now. Do some reading and see what others have to say. I'm going thru the same problem right now. Have not come across "the" cure as of yet.

 

[Chris1956]

Re: 76 Merc850 set-up & tuning

You might check idle pickup timing and max spark advanc to make sure those are correct. There is a link and sync for inlines in the FAQ section. if these are OK, you likely need to set the carb idle mixture screws. start at 1-1/2 turns out, and adjust in the water (motor warm) until you get nice smooth idle at 800-900 RPM. Now try to accelerate. If motor stumbles open top carn 1/8 turn and repeat. If it still stumbles, open bottom carb 1/8 turn. repeat sequence until motor accelerates well and idles fairly smooth.