1973 Merc 850 dies running wide open

[Clembone]

I have a 1973 Merc 850 that runs great when you first start out. You can run it all over the lake to your first fishing hole. Start it back up to move and you will be tooling along when out of no where it is like you run out of gas. Gas is not the issue. Engine will fire right back up and run but it will die again. You can run at low speeds without a problem. I am stumped. This is my first boat so I am all new to this. I have cracked the motor open to look for obvious issues but do not see any. I did notice that the top carb is spotless and the lower one is dirty with what looks to be oil and fuel. The lower part of the case is also gooped up with the same. Looks like I will be attempting cleanup and a carb job. Any help to this newbie to the boat scene will be greatly appreciated.

 

[crazycanuck]

Re: 1973 Merc 850 dies running wide open

hey there....i'm having the exact same problem with my 9.8 110 h.v.....let me know what you find out...

 

[timmathis]

Re: 1973 Merc 850 dies running wide open

Well I really dont know where to tell you start. You will have to go over it with A fine tooth comb!To find your problem. First thing you need to get A manul. And on the oil on the lower carb Is normal! Tim

 

[Clembone]

Re: 1973 Merc 850 dies running wide open

Funny you should mention the manual. I ordered sel1406 last night. There was a place to get the shop manual. Does anyone have recommendations about manuals? Should I have both?

 

[ehenry]

Re: 1973 Merc 850 dies running wide open

If you can get a factory manual for your particular engine thats what I would get. The Seloc and CLymer manuals are generalized and cover a plethora of engines.

 

[Paul J]

Re: 1973 Merc 850 dies running wide open

My 50 merc did the same, never got over 2000 revs<br />ended up being a blocked jet in the bottom carb.<br />cleared this and installed some in line filters<br /><br />Paul J<br /><br />This was all after changing ht leads and spark plugs etc

 

[Clembone]

Re: 1973 Merc 850 dies running wide open

I appreciate the posts but my Merc does go to full throttle and maintains it with no problem. I will try to clarify the issue. While you are cruising the engine dies. You can fire it right back up and take it to full throttle only to experience the same problem. It is sporadic in nature but only seems to happen after you have been running the motor for 20 min or so. When this problem occurs you can back the throttle down so that you are running about 10 mph and it will run all day at that speed. But who wants to do 10mph when you can do 35mph. I was going to start with the cooling system. I do see that the pee hole is pumping out what seems to be sufficient water. Is there a way to tell if your flow is sufficient? Could this even be a cooling issue? <br /><br />Thanks

 

[Clembone]

Re: 1973 Merc 850 dies running wide open

I have also disasembled some of the motor for cleaning and inspection and noticed that the rectifier is cracked. Could this be the issue? Can't wait to get my manuals so I can really rip it apart

 

[Clembone]

Re: 1973 Merc 850 dies running wide open

Well after talking with one of the repair techs at a Merc authorized repair facility. I put my motor back together and she ran like a champ??? Go figure..... You should have seen the look on the tech's face when I asked my first question about a 1973 Merc. He laughed and stated good luck on that antique. He did offer up a few tips but he was ready for me to leave after the first question.

 

[papasage]

Re: 1973 Merc 850 dies running wide open

most delers want to sell you a new one . cant blame them but some of us cant aford a new motor . <br /> i have a blown 85 1974 . part motor . need some parts for a 65 hp . papasage10@yahoo.com

 

[Clembone]

Re: 1973 Merc 850 dies running wide open

Well the issue is back. Got the parts to do a lower unit, carb, and fuel pump. Looks like I will have a blast this weekend. I will up date this as I think it is a fuel pump issue. More to come.<br /><br />

 

[rogueflyfisher]

Re: 1973 Merc 850 dies running wide open

I've got a similar problem with a '68 Merc 500. Please let me know what you find out. I was thinking the fuel pump was the problem also. It runs great off the bat, then after trolling for a few hours, it will sputter at full throttle. Then the fuel pressure (the ball on the fuel line) will be soft.... an barely gets the boat on plane. ???

 

[Wreck Rider]

Re: 1973 Merc 850 dies running wide open

Had similar symptoms last weekend with my '76 model 850. Starts, idles, moves around, but at full throttle it'll jump onto plane and then drop power, come back up again right away, just like the tank is empty. It'll start up again too and run at low throttle just fine. Just to troubleshoot my buddy pumped the bulb as soon as the full throttle problem came on and the motor pretty much ran perfect as long as he was pumping. <br /><br />It turned out to be a leak at the fuel filter cover. At idle or low throttle no problem but at higher fuel flow the pump was sucking air through the leak. We found it by taking the engine cover off and pumping the bulb tight, it showed a small fuel leak, I guess the air leaks in a lot faster than fuel can leak out.<br /><br />We had to go to six places and spent 3 hours searing but finally a standard automotive o-ring fit just perfect and we were off again.

 

[Black69]

Re: 1973 Merc 850 dies running wide open

Do you happen to know the size of the o-ring. This seems to be a problem area in my 850 also and would like to carry some spares.

 

[Wreck Rider]

Re: 1973 Merc 850 dies running wide open

Sorry, I did it by fit by taking the cover into the shop with me and hoping, don't remember the size.