Fuel in the Water

[JARB]

I recently bougt a small 14' boat with a 1996 Yamaha 30 ESRU 2-stroke motor. It was running a bit rough at idle, spitting and stalling and fuel could be seen in the water at idle. At speed she ran good.

I dissambled the carburetors, cleaned them in an ultrasonic washing machine so they are absoletely clean. Installed a repair kit and since the idle needles were quite worn at the middle and lower carb I replaced them as well. To be perfectly sure everything was in order i also replaced the low speed fuel jets although they looked OK. The low speed air jets cannot be bougt as spare but they looks perfect.

The carbs have been synced and adjusted according to the repair manual. I have installed new gaskets and diaphragm in the fuel pump, new thermostat, new sparkplugs and checked compression - 135 on all three cylinders.

The engine now runs perfect, normal 2-stroke smoke. I can idle for half an hour and then just slam the throttle lever to the bottom and she responds immediately without any hesitation all the way to WOT at 5400 rpm - But still sometimes gas in the water at idle.

The engine is a short shaft and the boat has a rather deep Vee for this size of boat so the engine sits low on the transom. I have now noticed that fuel in the water only shows up when the exhaust relief ports becomes submerged, as long as they are above the water - No gas in the water.

Is there any guidelines for the engine height and should the ports always be above water? Or is my symptoms indications of something else not beeing right with my engine?

[boats.net]

Did you replace fuel pump diaphrams when had carbs apart, it may have hole in it, is spark good, firing on all cylinders?

[JARB]

Yes, gaskets and diaphragm in fuel pump is also new, that was one of my thoughts too.

She idles very nicely and runs like a champ at higher revs so I think she fires like she should. My timing light went out but I will check the timing with my new one and also see if she skips out but as I said she idles very nice and even after idling for a long time she answers to full throttle without hesitation so I doubt it..

As far as I can see in the manual the ignition system is very simple to measure. I will measure the resistance in the pulser, charge and ignition coils according to the manual and get back with the results.

Any thoughts about engine height or other faults causing this? I only get gas in the water when the exhaust relief port is submerged..

Thank you very much for Your reply!!

[boats.net]

The exhaust holes shouldn't be under water(may be mounted too low) but shouldn't cause it to leak gas.

[bumperfood]

You know what you are seeing might just be normal. At speed the exhaust will mostly exit through the prop and at higher speed you wouldn't see any oil in the water. At an idle, and the exhaust ports are under water, you may be washing off gas/oil mixture in the leg. It takes very little oil to cause quite a sheen on the water. It is also possible that you are getting too much oil pumped into the fuel at idle. Sometimes this can happen if you change to synthetic in an engine that was originally designed for dino oil.
You may find that you need to raise the engine, to keep the ports out of the water.

[JARB]

Yep, the way she is running is in fact indicating that everything is in quite good order. A rich running or misfiring engine should not run the way this one is doing.

In the picture there is no one in the boat and when she idles in this position there is no gas or oil in the water. When I jump in the boat the exhaust port gets closer to the surface and sometimes it dips under or get splashed by a wave and then there is gas in the water..

All carbed 2-strokes looses some fuelblended scavenging air when running, well that is in fact one of the causes of their poor effiency :-) Normally this fuel is in vapour form and exits the exhaust port invisibly. When my exhaust port gets splashed or flooded the fuel vapour condenses on the water surface. Thats one of my thoughts around this..

The oil injection system is still in place and the link is adjusted to specs, although I havent actually measured the output from the pump. But I consider the oil consumption normal, I have burned around 25 gallons of fuel so far and it has used less than a quarter of Yamalube 2-M oil, making the ratio around 100:1.

I live in the southern part of Sweden in Europe and winter is late this year. Normally we have snow and ice this time. My plan now is to measure the ignition system and winterize her. During the winter the boat will undergo some modifications, shifting weight forward and raising the engine an inch since the AV-plate is buried at this height in planning speeds.

Thank You all for Your replies!