Outboard carb ‘overflowing’

[chris-s]

What would cause fuel to spray out of the two brass pipes on top the carb? It’s coming out at quite a rate.

It’s a mercury 6hp 4S with a brand new carb as the original had been mullered by the previous owner.

I had it running nicely in the bin at home tho the plug was getting very black/oily in no time at all. Tried it on the water today and it wasn’t great, ended up with a lot of rowing.



Chris

 

[penfold]

If the plug was oiling up it wasn't "running nicely". What was on the pipes previously?

 

[chris-s]

Nothing was on the pipes. On previous engines with similar/same carb they just have short pipes leading’s inside the cowling to drain but I have never seen them spray out the amount of fuel this was doing earlier.

 

[rogerthebodger]

Manual for engine age 95 onwards shows carb detals

http://elrincondepitagoras.es/PAGIN...ry Mariner 4, 5, 6 4 Stroke Sevice Manual.pdf



A non function float needle valve would cause fuel to overflow the carb and cause black plug running

 

[penfold]

A gummed up or jammed needle valve would certainly do that.

 

[thinwater]

Needle valve. Probably was installed crooked. Easy fix.

Also, if the fuel tank is pressurizing that can contribute. Install a cut-off valve, or better, a demand valve (Attwood sells them).

Some models take the vents into the intake before the carb. You can also put a lawnmower fuel filter on them to reduce evaporation and gumming in the carb, and keep bugs and dirt out. They really should at least have a screen.

 

[chris-s]

Think it might have been the float needle, with the float right up it wasn’t shutting off. It was overflowing on priming, not sure how I didn’t notice that after fitting it the other day. A slight tweak and it doesn’t overflow and the plug seems cleaner after a comparable run in the bin. Will try it in anger tomorrow.

Thanks!

 

[Steve_N]

My Mariner 4 (same carb.) has started overflowing twice in the past 6 months, even with the float level set correctly, and it has been debris in the needle valve which seems (the debris that it) to have come from E10 fuel evaporating in the float chamber. The residue the stuff leaves behind has to be seen to be believed. Running the engine until it's starved of fuel still leaves some fuel in the float chamber and draining the chamber manually is a bit of a faff to do very time.
Mine has both internal and external tanks and I now put ethanol-free fuel in the internal tank and run this through before shutting down. Thus far it seems to have been the solution.
I use the method in many Youtube videos to remove the ethanol as no E0 pump fuel is available around here, although alkylate fuel would do the same job.