Yamaha 2 Stroke 200 V6 Dying

[Chris_in_Oman]

Hey Guys,

Just new to the forum but need some advice about my engine.

I have a 200 Horse v6 2 stroker on the back of my boat. What has been happening is when at higher power (3500 revs and above) after a while of running, the engine starts to lose power, and if the throttle is left open in the same position will eventually cut out (losing power slowly until it does so). Usually then it sounds very rough when restarted, and vibrates a fair bit to be honest, but then after a while it comes back into normal running. There seems to be no set time limit when this happens, but when we run the boat to begin with, it seems to run for a good 15 minutes with no problem. After then the time generally reduces for the loss of power. This happened when we 1st bought the boat, so we naturally took it to Yamaha and had it serviced. They said it had a clean bill of health, and actually commented saying it was a strong engine. But, after a while this still continues. I thought it may (and still could be ) a fuel starvation problem, or old lines becoming pourous. So worked my way back from the engine to the tank. I have now replaced the priming bulb, and all fuel lines back to the tank, and the inline filter downstream of the tank. For good measure we emptied the tank incase there was excess debree in the tank. There also does not sound like its missing on any cylinders.

The problem still continues. Could anyone suggest what may be wrong and where to go next??

Thanks

Chris

[TownsendsFJR1300]

There should be an under hood fuel filter (probably on the starborard side). It's a clear (probably yellowish now) plastic cup that should have nut securring it.

Pull that bowl (regular thread) and filter and inspect. I'd pour that fuel into a small container and inspect for any water separation as well. If the filter hasn't been replaced in a year or two, I'd replace it in either case (preventive maintainance)


Also, if you have a separate (you should) fuel water separator mounted on the rear of the boat, again, replace it if it hasn't been done recently. I'd check the fuel, contents same as you did for the engine fuel filter.

With the ethonol fuel, its not un-common for it to literally break down the inside of older fuel line. That crap, works its way up into the filters.

Draining and catching the fuel in carb bowls (for inspection of crap, water, etc) will give you an idea of the condition of the fuel system...


Good luck..

[99yam40]

The fuel system can be checked for pressure and vacuum to see if there are restriction tank, pick up tube, lines, etc.
Have you checked the lift pumps yet?

Have you tried pumping primer bulb while problem shows up to see if that helped?

You can also temporarily install a clear piece of tubing after fuel pumps to check for air being sucked into the system from connections not sealing properly

Checking for spark on all plugs can be done by hooking up a timing light to the different plug wires while problem happens or using a spark tester

[Chris_in_Oman]

Thanks Townsends,,

As i say between the engine and the tank, ALL lines have been replaced, as well as the inline Fuel / Water seperator.
We recently had the engine serviced, but not sure if the Fuel filter inside of the Engine cover was replaced as part of this, i will go back to the dealer and check what parts were changed / inspected etc.

Thanks for that

99Yam, the clear tubing sounds like a good idea too, i will also get a pickup / pressure test done, as i feel it is tank side of the engine that is causing the problems, The fuel bulb does not stay as firm as i think it should, in some cases appears to be struggling to keep shape and not collapse in on itself. I dont think there is an issue with the spark plugs as it sounds sweet as a nut when it is running prior to it slowing, not missing or anything.

Again thanks, will let you know how i get on.

Cheers

Chris