1971 Merc 800 80hp wont stay running

[clueless75]

So I took the boat out to the river yesterday only to find that when I start it, it only lasts about a minute at best. Fuel tank is full, fuel primer bulb is hard, fuel tank vent is open, no fuel leaking anywhere... I'm clueless! (Hence the name). I got this boat through a trade for a go kart (of all things) and there were many problems. First, all the wiring from the internal wiring harness needed to be redone (which I did by splicing the wires near the bottom since a new internal wiring harness would cost over $300 or something ridiculous), both carbs leaked (which I fixed by replacing with new floats, although one valve was a little sticky sometimes), and the wire from the coil to the distributor was barely hanging in there which actually fell out later, so I had to replace that as well. Yet somehow, it miraculously started when he showed me. Anyways, I fixed all of those things and here I am, without it running very long at all. When it starts, it's at either full, half, or no throttle and runs fine for a bit then misfires for a second or two, sputters, and dies. Also, if it runs and I try to accelerate/decelerate it will do so for a bit but will also die. It seems as if it's on a timer to just give up after a minute haha. Any help would be appreciated to solve this mystery, thanks guys. (the pictures didn't turn out good but oh well)

 

[merc850]

Did you replace the fuel pump diaphragm? When you pump the ball you fill the carbs and the internal lines and that will let it run for a few minutes but without the pump working it will stop.

 

[clueless75]

No Title

Ah, thats one thing I forgot to check! I'm sure that thing would be old and brittle, and it would be a great place to check. I must also mention when i was pulling the fuel filter, the thing was FULL of brown-coppery stuff (see pic). i completely forgot about it until now, and may be suspect to something that i haven't gotten to yet. Anyone know what it is?

 

[GA_Boater]

Looks like rust to me. See if it's magnetic. I think rust is attracted to a magnet.

Do you have any inline fuel filters between the tank and motor?

 

[clueless75]

I don't think it's magnetic and there are no inline fuel filters at all, anywhere

 

[clueless75]

Fuel pump appears fine, what's next to check?

 

[tommarvin]

You have a project, that rust looking stuff could be the inside of a very old fuel filter, or the gas line, or in the tank? I would have a 10 micron spin on water separating filter installed close to motor on transom or side wall.

It sounds like a no fuel problem, can you take the fuel line off after the fuel pump and see if it pumps gas?

Replace all on engine fuel filters, and take the carb bowls off, check float switch, get the largest drill bit that will fit in idle jet tube and gently clean it out.

 

[clueless75]

The fuel lines are all old and deteriorating, so I'm going to replace all of those. As for the fuel pump test, I wouldn't be able to do because the fuel line below it has crumbled and fallen off, so that's going to be replaced. I also noticed (and you can kinda see in the one pic) that the fuel line kinda dips after the fuel pump, and I thought the fuel pump only sucks and doesn't push? So would the fuel after the fuel pump be led by gravity to the carbs or does the pump pump it to the carbs too?? And how can I get at the idle jet on these carbs?

 

[Texasmark]

If non-metallic then go after your fuel line. I found chunks of tan/light brown crud in my fuel line after only 10 recent years of operation. In 50+ years of boating, I never had a problem like that and ran Mercs at least the last half of that time.

If metallic, what's your tank made of? Regardless, if your tank is steel, even if it was terne plated inside rust is not uncommon with older steel tanks. Every year they go through a sweat during large temp changes, especially when cold and high humidity, and that just eats away at the plating. Since most tanks have a screen filter in the tank, you are getting what gets through the screen. Only reason you are still getting good fuel flow is that the surface area of the screen is large and probably only part of it is submerged in rust.

Rust is Ferrous Oxide which should be magnetic. I have never tested rust alone but I know heavily rusted steel parts will still easily conduct magnetic lines of force.

 

[clueless75]

I can't check if it's magnetic since I cleaned it all up and don't have any to test. As for the tank, I am running with an older plastic quicksilver one - however, the previous owner may have been using a metallic one. I've noticed in the picture that there are small black chunks that I would assume to be the fuel line along with the suspected rust.

 

[tommarvin]

Good for you to replace all the fuel lines with the best its called somethingA1-10 coast guard., you don't want a fire or explosion out there from a fuel leak..

I think the fuel pump pumps to the carbs. You get to the idle jets, by removing the carb bowls, the idle jet is in the center, get the largest drill bit that will fit in the idle jet tube and gently clean it out, blow compressed air in there too if you can, is the float switch ok, everything is clean inside.

I would get a service manual, it makes repairs and maintance ordering parts very easy.

 

[clueless75]

The carb bowls don't come off, they are all part of the carb but the top part comes off with the fuel filter and such inside it. When I took it apart one float switch was fine but the other was a tiny bit sticky, and I would assume that the fuel would at least gently push it open as it want too sticky... Is that a problem?

 

[Texasmark]

I can't check if it's magnetic since I cleaned it all up and don't have any to test. As for the tank, I am running with an older plastic quicksilver one - however, the previous owner may have been using a metallic one. I've noticed in the picture that there are small black chunks that I would assume to be the fuel line along with the suspected rust.

Yepper on the fuel line. On another thread I talked about a problem I had with bogging on the hole shot and it was just that....a black piece of fuel line lodged in one of my 3 high speed jets. But that fuel line problem was in the engine. The other problem with the tan chunks of scale was the OEM Quicksilver/Mercury gray colored slick (silicone???) fuel line.

 

[clueless75]

No Title

Here's a schematic of my carb; is number 22, 23, and 24 what I need to clean out or number 27 and 28? 27 and 28 is the idle adjustment screw and 22, 23 and 24 is listed as the "idle tube". Which one do I clean? http://www.crowleymarine.com/mercury-outboard/parts/445_90.cfm is where I find all this.

 

[Texasmark]

28 is your low speed adjustable jet. 31 is the non adjustable high speed jet. You need to ensure that all the holes in the carb and venturi suction tube are clean. Sometimes a spray like Berryman's Chem Tool aerosol works, sometimes you need their liquid and soak it, sometimes you need to run a fine wire through the holes and when finished with all that a heavy dose of 100 psi air.

 

[merc850]

You should replace the wires in Pic. 1 they run to the stator (Yellow) and the Red one runs to + power, if the red wire disintegrates the rectifier and stator could be damaged.

 

[clueless75]

You should replace the wires in Pic. 1 they run to the stator (Yellow) and the Red one runs to + power, if the red wire disintegrates the rectifier and stator could be damaged.

I replaced all wires except from the rectifier to the stator as they seemed in good condition... Is it important to change those wires?

 

[merc850]

They look corroded and fragile to me, remember the motor doesn't sit still it takes on stresses while running.

 

[clueless75]

The wires from the rectifier to the stator are pretty strong and intact, all the other wires were not, so I replaced those but left the two wires to the stator alone since they were fine

 

[clueless75]

No Title

After taking apart fuel pump, everything seems alright (to me, that is). Does anyone see anything wrong? Should I get a new diaphragm? Any thoughts???