Nagging problem w/850 merc cutting off

[roger3645]

Okay I’ve had this issue with this motor since last summer and it’s driving me nuts. 1975 850 85 hp merc. Problem is it’ll just cut off while approaching high rpms and then it’ll start right back up. What I’ve done so far: Removed and cleaned carbs, ran 3 treatments of sea foam thru it. I’ve jumped the red wire and white wire on the switch box and have done the timing & snyc of mercury inline as posted by Clams. Results: Nice idle in neutral and in gear with a good hole shot. I’ve also ran the motor with a different remote control box. I don’t suspect it is fuel delivery as I have a good firm ball and have used the gas tank and gas line on another motor with no problem. Compression is good on top 3 cylinders (unable to get to #4). Now the motor does not stall or sputter it just cuts off. Seems electrical. Could it be the switch box? I bought the switch box off ebay and it came off a 135 merc inline 6.

 

[roger3645]

Re: Nagging problem w/850 merc cutting off

Okay the compression wasn't as good as I thought #1 145, #2 140, #3 90, still unable to get to #4.

 

[deejaycee_2000]

Re: Nagging problem w/850 merc cutting off

My 90hp merc did the same, but luckily in my situation I just replaced all the fuel filters and the problem was solved, I have a built in tank and collected alot of crud over the years. Maybe you need to have a look at that ...

 

[roger3645]

Re: Nagging problem w/850 merc cutting off

Don't think it's the tank or filter as it is a portable plastic tank with an inline fuel filter. I've used it on another 85 hp merc without any problem.

 

[mikmic2]

Re: Nagging problem w/850 merc cutting off

Condenser???? I thought maybe it's charging up and shorting out or some goofy thing like that. Of course maybe yours doesn't have points. <br /><br />I hate those electrical problems. <br /><br />Or, perhaps your wiring harness is shorting out somewhere when you reach that certain throttle position. I was speaking of the wires that go under the flywheel. Sorry I can't help you more, after the help you gave me.

 

[Chris1956]

Re: Nagging problem w/850 merc cutting off

Roger, You may have a fuel pump problem. If you can get someone to pump the primer bulb while you are underway, and the motor doesn't die out, that should clinch it. If so, you can rebuild the fuel pump(s) quite easily.

 

[roger3645]

Re: Nagging problem w/850 merc cutting off

Chris already replaced fuel pump. Thanks