Carb Troubles

[This_lil_fishy]

Engine: Mercury 50
Serial #: A952338
3 Cylinder 2 Cycle

I believe this engine to be an '86 model with dual carbs. The carbs are fairly simple compared to some I have seen...but then I have never been very good with carbs.

My problem, I can start, and get the engine running just fine. While the engine is running there are no problems. However, as soon as I shut the engine down fuel slowly builds up and starts leaking out the airbox as well as down the butterfly tubes of both carbs. It will leak for a few minutes (a fair bit of fuel) then stop. The fuel does not seem to leak again even if the bulb is pumped up and held. Only after shutting the engine down does this seem to happen.

I have added a full can of Seafoam to the fuel tank (3 gallon tank). I have also disassembled the carbs a dozen times and checked the float and needle in each. I've cleaned the needles and seats each time, and they always seem fine and clean. I've adjusted the floats up beyond what I 'THINK' they should be at, currently about 7/8". I've measured the height from the carbs gasket surface to the top of the float (when the carb is held upside down and the needle and arm in place). I can't imagine the floats should be higher as the bowl is only 1" deep. So I have two questions: 1, What do I do now? 2, What is the float level supposed to be for this motor?

I do not have access to the service manual right now, unless there is somewhere I can D/L one. Any help would be appreciated.

Ian

 

[This_lil_fishy]

Re: Carb Troubles

New information:

I've brought the carbs into our shop to run through our parts cleaner, I pulled the bowls off, and set the carbs in the bin upside down (just the weight of the floats on the needles) and applied the cleaner to the fuel line feeding the carbs. Even with the fluid pressure, no fluid was comming past the needles. If I lift the floats a pin the pressure shoots the needles out....I am at a complete loss...why is fuel filling the carbs when I shut the motor down then?

PS: The floats are solid foam, gonna try to test them to see if they actually float later...ever hear of them becomming 'water' logged?

Ian

 

[j_martin]

Re: Carb Troubles

New information:

I've brought the carbs into our shop to run through our parts cleaner, I pulled the bowls off, and set the carbs in the bin upside down (just the weight of the floats on the needles) and applied the cleaner to the fuel line feeding the carbs. Even with the fluid pressure, no fluid was comming past the needles. If I lift the floats a pin the pressure shoots the needles out....I am at a complete loss...why is fuel filling the carbs when I shut the motor down then?

PS: The floats are solid foam, gonna try to test them to see if they actually float later...ever hear of them becomming 'water' logged?

Ian

On the V6's, we replace any foam floats we find with hard plastic ones. Ethanol sunk the foam ones by now. Carb cleaner is known to sink em immediately, as would some of the fuel additive cleaners.

hope it helps
John

 

[hkeiner]

Re: Carb Troubles

I've cleaned the needles and seats each time, and they always seem fine and clean.

If I had your problem and the the problem persisted after replacing the floats, I would next consider replacing the needles and seats. While they may seem fine and clean, perhaps they are worn and causing the fuel leakage. Just my thoughts...although I would agree that sinking floats are the likely problem.

 

[This_lil_fishy]

Re: Carb Troubles

Well, I put the floats in a bin of cleaner, and sure enough they float, but not very well. I also noticed the rubber seal at the bottom of the butterfly shafts is pretty worn, barely touching the shafts. So I say screw it, and have broken down and ordered a completed gasket and rebuild kit with floats. Enough screwing around, figure I may as well rebuild the pump and replace the filter and lines while I am at it....

I'll let you know how it all works after that.

Ian

 

[This_lil_fishy]

Re: Carb Troubles

Just an update for those that are having a similar problem...with very little response.

With the merc's I found out that the replacement floats are plastic, and include 1 needle and seat. Included in the package is a note that says that if you are replacing the floats you MUST replaces the needle and seat as well, and vice-versa.

Unfortunately for me the mercury dealer here is not very concerned about my order as I am not paying them to do the work I guess, so, so far I have only received one kit (my engine has 2 carbs). I figure I may as well rebuild one carb and use the best left over parts to put the other carb back together for the time being, as it is a long weekend. I was promised I would have all the parts by the long weekend too..but that is another story. Anyhow I carefully re-assembled both carbs, the top carb has all new parts, and the bottom carb has the lightest of the two floats (I weighed them on a postal scale, and one was definately about twice the weight of the other). I re-assembled the engine with new fuel lines and such, and after a bit of fuss managed to get the engine started and running. Runs as well as one would expect with a 100:1 mixture (different story also, new fuel will be added so that mixture is back to 50:1). I shut the engine down and the top carb is perfect (all new parts) and the bottom carb is much better, but still a minor fuel leak after being shut down.

Motto of the story, if you have a fuel leak out your carbs, replace the needles and seats as well as the floats. Mercury must know something that they aren't telling anyone directly. Also worth mentioning, if you have foam floats, throw them out. They are very inconsistant, I forget the actual weights but I clearly remember the doubled weight from one to the other. Also if your carbs have rubber seals at the bottom of the butterfly shafts, you have to order that seal seperately as it is not included in the gasket set, oddly enough the float seat copper gasket is in the gasket set, as well as the float kit so now I have spares. Also that little rubber gasket is MORE expensive then the entire gasket set, but worth the cost.

Ian