trouble with 1974 mercury 850

[andy h]

First Off I just wanted to thank everyone for all the valuable info i have been stealing off of this site. But finally I could not find my question answered by the search feature, So I figured it was time to register.<br /><br />Second- I ain't no friggen boat mechanic!!! these things drive me nuts I own a 79 90 hp mercury and a 74 85 hp mercury and I don't know what one is the bigger headache. <br /><br />OK my question (finally) I bought the 85 hp about 3 months ago, the owner said it had sat for 2 years, I took it home shot some oil in the cylinders changed the plugs changed the lower unit oil and the impellar, and fired it up, ran perfect. I did not touch the carbs, I figured if it aint broke don't fix it (yeah I'm a dumb ass) It ran "OK" for about 3 trips then on the 4th trip when i was stopped to do some fishing it would not start back up I had to prime the crap out of it choke it and give it full throtle. and when i did get it running it would shut of as soon as i put it in forward or reverse. I troll motored back to the dock and took it home, it ran great on muffs shifted perfect, took it back to lake same problems.<br />WHAT IS UP could something be wrong with carbs?? I'm sure that's what it is since thats the one thing that i hate working on (all those little parts make me nervous) any info would be greatly appreciated fellas!!!<br /><br />sorry for the super long post but you people always say more info more info so I hope this is enough to work with.

 

[MercMark]

Re: trouble with 1974 mercury 850

I have virtually the same engine. Merc 850 thunderbolt mid seventies. It's been headaches for me too, and I've heard different things.<br /><br />I had mine worked on two years ago by a mechanic/family friend. He redid a bunch of stuff in the lower unit and had his guys tune it over and over and couldn't get rid of the problem, as soon as you drop it into gear it wants to stall unless you give it a little shot of throttle right away. (pain in the ass for skiing)<br /><br />I later took it to another guy who was supposedly going to rebuild it for me (I don't think he touched it because I still had the same problem) Second guy told me I had it overpropped and that's why it stalled when you put it into gear. Even though I have no problem getting revs out of it on plane and no trouble planing up.<br /><br />The two things that heard over and over through this whole process was:<br /><br />1- We don't touch the 85's, they're nothing but problems.<br /><br />2-All of the four cylinder mercs where solid reliable engines.<br /><br />So ??????<br /><br />Since all of this I lost cylinder No.2 and I'm about to rebuild it myself. I figure if you want it done right do it yourself. I'll let you know if I can cure the problem.