Selva/Yamaha 50hp 4stroke conking out

[thomas]

Hi all,

I recently bought a 4.5m Valiant with a 5 year old 50hp 4 stroke Selva, re badged Yamaha, from a friend of mine, it had been sat in a river and had less than 20 hours use and as far as I can make out had never been opened up as the river has a 8 knot speed limit - I know what I was buying and aware of the history and it was serviced.

I had it serviced again locally and took it out today, I was having a problem with it dieing when I went to engage gear and at a low RPM and it did not sound healthy but when it I gave it some throttle it was fine, it seemed to clear itself so I headed out of Chichester to open it up (had arranged to meet a friend at West Pole just in case of problems).

It was running fine, though seemed a little underpowered for a 50hp on a boat that size, after about 10 mins the problem came back and it would not idle at all and it sounded terrible at low RPM so we towed it back into the harbour, where as before it would come back to life it remained sick every time I tried it, periodically on the trip back to the marina.

I have a warranty from the service and will take it back next week but would love to know what the problem could be.

[matt h]

Water in float bowls of carbs (im guessing carbed model) !!

[ribber]

You haven't used 5 year old fuel that came with the boat!
That's the only thing that may have been different after your mechanics service, as I assume he had it up and running to carry out his work!

Otherwise, it doesn't sound like much was carried out by the mechanic.

[thomas]

Thaks, yes, carb model and no, it has new tank and fuel.

It seems similar to other problems I read about with low pressure fuel pumps bur I don't think I have one.

[jyasaki]

Low pressure fuel pump is specified because of the way injected engines work: the low pressure fuel pump pulls fuel up to and into the motor, then the HP pump generates a higher pressure in the injector rail that feeds the injectors.

A non-injected motor will still have a LP pump, but it will simply be called a fuel pump since there is no other pump to differentiate it from.

You can usually ID a fuel delivery problem by squeezing the primer ball and seeing if things correct themselves. If so, the problem could be the pump itself, a leak in the fuel line (air ingestion), a plugged, kinked, or obstructed fuel line or filter, or insufficient venting of the fuel tank. Or several other things, but these are the most likely, I think.

jky

[wavelength]

carbs-float valves sticking shut due to lack of use and stiction ...??

[thomas]

I had the carbs taken out and cleaned last week, put back and it was fine but as soon as we opened up yesterday it happened again on just one cylinder.

I replaced all the fuel lines, new tank and put fresh fuel in and there is a separator in line.

If he'd cleaned the carbs out would the float valves still stick?