Water in fuel

[NickT]

Hi chaps,

I foolishly went out to see the round island race where it was blowing a F5 at least.....

My logic was that if something happened then there were 1000 boats who may assist me!

Water was occasionally coming over the windscreen and later in the day on my way back from Yarmouth to Hamble the engine started to slow down, I thought the throttle was slipping back but no the engine was dying...

Luckily my friend was in Lymington and I called him up on the vhf and he towed me back to port.

I called seastart and they met me at the pontoon where the chap changed the fuel filter (I carry a spare) and flushed water out of the fuel line.

Plugs out and cleaned and the engine started and sounded good. I was escorted out of the harbour and made it back safely to the Hamble.

I have subsequently fitted a water separator and filter to the boat to prevent any future occurrences.

To cut a long story short I still have a problem when running at high speed, the engine slows and it seems that water is still in the system.

I have drained the carb bowls 4 times, flushed the fuel filter and drained the diaphragm pumps but the problem persists.

Tick over up to 2000 rpm is fine, the engine is like a sewing machine.

Any ideas on what I can do to fix this please?

Engine is 2001 mercury 75 four stroke with carbs.

[mlines]

Is it water that causes the issue, perhaps you have shaken dirt up from the tank bottom and blocked a jet?

If it is water then drop a water removal sock in the tank or pour in water neutraliser

Sent from my Nexus 6P using Tapatalk

[NickT]

Hi Martin,

The fuel filter captured any debris I think. I suspect that it is residual water in the fuel lines. It would only take a thimbleful to cause problems.

The idle jets seem OK as it is running well up to 2000rpm. When I open up the main jets take over and I guess any water in the bowl will starve that carb.

I may have to get the carbs stripped fully and reset professionally as you need vacuum gauges to set up I believe.

[Ianfs]

Hi Nick

It doesn't sound like water in the fuel to my limited knowledge. Didn't Grumman in WW11 use water injection to increase power and in damp weather engines run better, but I'm probably way off Base here.

From your description of the problem it sounds as if you can't get enough fuel into the engine at higher than 2000rpm i. e. a suction problem or blockage and I would have thought it would misfire rather than slow if it was water.

I had an Evinrude 50 once and used to race Water Buggies with a Suzuki 20 and both had portable tanks with breathers which I had to unscrew otherwise the engines would die at high revs.

Consequently, maybe the water thing is a red herring and you have a fuel pump problem or a fuel line problem.
Just a thought.

[NickT]

Hi Ian,

Thanks for your response

Since draining the carbs things have improved significantly.

I think there is still somewhere that is holding some water and occasionally a slug of it hits the carb bowls.

I am going to change the plugs as a precaution but will also disconnect every fuel line that I can access and drain or flush through.

Failing this I think a complete strip and rebalancing of the carbs will be required.....

If that turns out to be necessary then I may ask the technician to fit the 90 hp main jets and remove the air restrictor on the air intakes.

I believe this is the only difference between the 75 & 90 versions.

Ed of this parish hopefully may have a view.......

[Ianfs]

Just a thought Nick, but have you done a compression test recently?
It might very worth getting that out of the way initially to rule out valves or head gasket.

Also a further thought, I can't see anywhere that you have drained the fuel tank. Do you think it possible that you have some water in the fuel tank? This might give you the symptoms you are describing.

Just a thought.