why does my motor keep conking out?

[nashton]

its a 1975 Mercury 850 (85hp).

I put new plugs, fuel filer, cleaned carbs. It starts and runs for a while and all of a sudden it just stops! I can pull a tube, drive around for a while--- and then all of a sudden nothing. And then it may or may not work well for a while again.

and yes, I do have the gas cap vented.

 

[Windykid]

Re: why does my motor keep conking out?

Might check condition of wireharness for cracks broken wires.

Does it completely die or drop to idle?

 

[nashton]

Re: why does my motor keep conking out?

Completely dies.

 

[Windykid]

Re: why does my motor keep conking out?

Sounds like a short maybe.

 

[Silvertip]

Re: why does my motor keep conking out?

Try and be a little more descriptive. Does it quit like you turned the key off, or does is sputter and die. Does it seem to slowly lose power before it quits. All of these conditions are caused by different issues.

 

[nashton]

Re: why does my motor keep conking out?

It quits like you turned a slow key off (if there was such a thing).

it revs down very rapidly and smoothly (like in a second).

so it does not sputter and die nor does it complely kill in a fraction of a second (like a key would).

thank you all!

 

[w2much]

Re: why does my motor keep conking out?

Check your fuel supply. Bad bulb, air leak displacing fuel. Had a similar prob spent all kinds of time trying to diagnose. Mine was a bad gas line connector(O ring inside would seat badly one time and be fine the next 5) .Sound like a fuel issue. Good Luck

 

[billybones]

Re: why does my motor keep conking out?

don't know if this will help, 10 years ago I had just about the same motor around same year. Just about the same problem. after a lot of things it ended up being this fuel line that ran under the starter motor. atl least I had to remove the starter to get it out. it looked ok. but eventually it started to leak. real slow. but first couple of months it did not but must have been rotted enough to let air in. but really only went out after motor was warm for awhile. some times ran good some times would just die out. Hth.

 

[Evinrude6]

Re: why does my motor keep conking out?

Check the switchbox, if bad, replace it.

 

[j_martin]

Re: why does my motor keep conking out?

I vote for the air leak in the fuel system.

John

 

[myusedNEWboat]

Re: why does my motor keep conking out?

Is this the 1st time you've had it out on the water this year? I had my boat out this past weekend for the 1st time.I was pulling my boy around on the tube then my motor just kept bogging down after a couple minutes then it would just quit.I was told several things it could be just as you were.After all the advice people gave me it turned out to be just bad gas from sitting all winter(I thought that's what the fuel stabilizer was suppose to prevent).After I brought it home that night I changed the spark plugs and added some stuff to my gas and let it sit all night.I brought it back to the water the next day and had no problems.I guess I was lucky.I was gonna start fixing all the things people were telling me it could be.

 

[nashton]

Re: why does my motor keep conking out?

No, not the first time. I put new gas in it this year as well. Thank you though. This weekend I am going to try to figure this out. Any other suggestions?

 

[nashton]

Re: why does my motor keep conking out?

If I prime the bulb it usually starts right it again.

Does this bit of information help the diagniosis?

 

[skibug]

Re: why does my motor keep conking out?

If I prime the bulb it usually starts right it again.

Does this bit of information help the diagniosis?

Sounds like either a bad/worn out bulb or trash in the fuel pickup in the tank. Replace the bulb and check for trash in the fuel pickup in the fuel tank.

 

[Rudy Brown]

Re: why does my motor keep conking out?

Check the switchbox, if bad, replace it.

x2.

 

[imported_skraps]

Re: why does my motor keep conking out?

I would vote for the heart of the engine Fuel Pump!

 

[studlymandingo]

Re: why does my motor keep conking out?

Nashton, you definitely have a fuel delivery issue if it starts back up after pumping the bulb. What type of tank do you have on the boat (aluminum or poly, and is it a below-deck or above)?

Check your fuel lines thoroughly, especially the connections. If the lines are old, go ahead and invest in some new ones; a new primer bulb would likely be in order if it has been awhile since it has been changed. The fuel pump is also an easy and cheap rebuild; and would probably be a good idea to go ahead and do that as it is good preventative maintainence. I rebuild mine every couple of seasons whether it needs it or not; I don't like surprises when I can't see the shore!​

 

[StriperLover]

Re: why does my motor keep conking out?

im sorry i dont think it is a fuel problem and this is why i have the same motor only its a 1973 merc 850 and i had the same problem 2 monthes ago. my problem was the switch box was malfunctioning and it would get really weak spark and the motor wouldnt run then after about 5-10 minutes it would fire right up like nothing was wrong. i beat my head in for 2 weeks untill i finally was able to check for spark when it wouldnt start and it was very weak or not at all. lucky for me i found a seized 850 at this boat mechanics shop and he sold me the top end minus the lower unit for 65 bucks and i got all the ignition parts i needed plus some extras .

 

[nashton]

Re: why does my motor keep conking out?

I am working of fixing the fuel pump, bulb, and fuel lines. If that does not work ill have to look at replacing that switchbox. Anyone know where to get a switchbox for my 1975 Mercury 850?

 

[mercerfisherman]

Re: why does my motor keep conking out?

Start with the obvious... Check the fuel filter first. (A visual inspection). Clean it out. Then I'd look at your gas tank and fittings, fuel lines, etc. Lastly, I'd look at replacing the fuel pump. Good luck.