77 merc 850 idle issues

Hi all,
I have a 77 merc 850. just got it, the boat sat for two years, its starts right up, but dies when I put it in forwad or reverse. The guy I got it from stated that he replaced the fuel pump, and after that it he could get his younger son up on skis with it. He said that he had some issues with hesitation. I thinking carb rebuild. It runs fine with in nuetral and on muffs, but not in the water. Is there anywhere I can find a diagram for this carb. The air/fuel mix might need adjusting too (I'm thinking). Just want to be sure I'm turning the right screws. I assume the carb is not vastly different from a motorcycle carb? And finally, what is the best source for a carb rebuild kit?
Thanks
Billd

Re: 77 merc 850 idle issues

I had the same problem with mine, i had taken both of the carbs off and had them proffesionaly rebuilt, the guy told me that one of the jets was clogged, he completely rebuilt them and set the screws to the right adjustment which he told me was 1 1/4 turns out now it ides great, shifts great out of water with the muffs but i have a problem now with it in the water that the timing is out (gotta get that checked) you might what do that to, the two screws that he had adjusted were on the front right side of the carbs (when you are staring straight at them) hope this helps.

Re: 77 merc 850 idle issues

Billd, The idle mixture is likely responsible for the motor dying when shifting into gear. You can open the mixture screws 1/8 turn at a time and the problem may go away. Of course if the carbs are dirty you could make it worse. Carb gasket kits and inlet needles for that motor are avail quite a few places.

Re: 77 merc 850 idle issues

when I did my 74 1500 I was surprised to find that a local shop had everything I needed including new floats. If that doesnt work out then oldmercs.com is a good source.

Re: 77 merc 850 idle issues

I'm struggling with the same stalling issue on my 1971 Merc 800.

Set everything up in the driveway on muffs and it ran great. Put it in the water first time Saturday and it dies going into gear. It starts very well and idles smooth but dies going into gear. If I goose the throttle a little I can get past the stall and then it will idle very well after that. I spent quite a long time double checking the sync and link setup and playing with the idle mixture settings. Got it pretty close now and 80% of the time it won't stall BUT I'm shooting for 100 % reliability.

Thinking the throttle pickup at 3-4* BTDC is a little low. Will readjust to 5-7* and see how that works.

I'm also running a mixture of Seafoam thru the fuel system so that may be cleaning things up as it runs. After running the motor for about 2 hours on the lake I did notice the idleing was improved.
There is an excellent thread on the sync and link procedure in the FAQ section here. Worth a read.