Mercury Outboard - Fuel overflow?

Tim Good

Tim Good

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My Mercury 3.5hp is acting up. It seems to dump fuel when the fuel is turned on. There is a small pipe from the top of the carburetor that appears to just spurt fuel out and dump it into the sea via a pipe running down to the base of the engine.

Can anyone diagnose the problem? Is this a valve stuck open?
 
northcave said:
My Mercury 3.5hp is acting up. It seems to dump fuel when the fuel is turned on. There is a small pipe from the top of the carburetor that appears to just spurt fuel out and dump it into the sea via a pipe running down to the base of the engine.

Can anyone diagnose the problem? Is this a valve stuck open?
Click to expand...

Float or float valve is the cause. Defective, stuck or dirty
 
Really simple. Your first repair should probably be nothing more than removing the float bowl (just 3 screws on mine) and cleaning it with 1/4 can of carb cleaner, focusing on the needle valve area, but hitting everything. That is probably all it needs and you can't do any harm. The bowl is the big bowl on the bottom. You generally do not need to remove the carb for this.

If that doesn't do it, yes, a more complete break down, rebuild kit , and manual are required, particularly since this sounds like your first.

13.gif
 
Easy fix, just take it to the dealers before you fck it up.

Hourly rates

Leave it to be repaired £10.00 per hour.
Offer us advice as to how to repair it £20.00 per hour
Help us fix it £40.00 per hour
You or your mate has fixed it before £75.00 per hour.
 
third engines said:
Easy fix, just take it to the dealers before you fck it up..
Click to expand...

We're constantly moving and currently in the Outer Hebrides. not really practical to just take it to a dealer. I'm sure that's fine for people that sit in marinas half the year.

Thanks Thinwater for the breakdown. Will clean out tomorrow.
 
northcave said:
We're constantly moving and currently in the Outer Hebrides. not really practical to just take it to a dealer. I'm sure that's fine for people that sit in marinas half the year.

Thanks Thinwater for the breakdown. Will clean out tomorrow.
Click to expand...

Since you have not identified the engine exactly I dont know how Thinwater can be sure that is the correct diagram!

If you tell us a bit more about the engine. 2 stroke or 4 stroke in particular and also some idea of its age and/or serial number it should be possible to confirm or find you the correct exploded diagram for the carb.
 
Last edited:
I'm not at all sure that is the right diagram. It was only to indicate where the bowl is typically located and to help the OP understand the sort of drawing he could probably find on the net. However, for my "just clean it without significant disassembly" suggestion--always the best place to start IMHO--you don't typically need detailed information for such a small engine . They are pretty simple, which is good.

To avoid future problems...
* Always close the vent when the engine is not running. This will keep the fuel fresh and dry.
* Use a good additive, like Merc Store-and-Start anytime the fuel is likely to last more than a month.
 
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