30 hp Yamaha Enduro 2004 model 2 stroke (Model 61TK)

[yamahafiji]

Hi,

I'm helping a local fellow here repair his outboard, I initially thought it was a head gasket problem and have since replaced it but this has not rectified the issue. It stalls at medium to high RPM coming in and out of proper revs, though never constant in keeping with those revs. Fuel systems appear ok, I cleaned the carburettour, fuel tank is OK. We checked the coils by swapping them over from each cylinder. It only appears to be the bottom cylinder that is playing up. All in all, Fuel OK, Ignition OK, Headgasket OK. This would only mean possible sticky rings or worn rings, but any advice you could give me would be most appreciated.

Thanks for your time.

[jb123]

check compression,fuel pump and try running with an auxillary tank hooked to motor filter.

[99yam40]

Sounds like high speed jet plugging, it is sucking air, or a fuel pump problem if it only acts up at higher RPM. Are you sure the high speed jets are clear? It does not take much to cause problems.
Use a pressure /Vacuum gauge to check fuel supply, a piece of clear tubing inline from the pump to carb to check for air, and use a timing light to check to see if the spark is going away or the timing is moving when it is not suppose to

[yamahafiji]

Thank you so much the info, It didn't even occur to me that the High Speed Jets could be sucking air rather fuel at a higher RPM, also the stator I will check that... I'm sure it is either of the above as I did suspect a fuel problem, but if it isn't that then perhaps it is the power pack (black mitsubishi box) that is playing up but I don't have the equipment to test it being on a remote island, do you guys know of any rudimentary things I could do to rule out the power pack being the problem? Don't know if they'd be compatible with a 40hp as there are plenty of those here.

Thanks for your time again, your doing alot of poor people a big favor if I can get it going again.

Thanks

[99yam40]

read this thread of test fuel system

HOW TO: Testing your boats fuel system. - iboats Boating Forums

Surly there is a timing light,pressure/ vacuum gauges, and clear tubing available to do some checking. If not you can always order online but the shipping maybe a killer.
You can buy and down load a manual online. It will give the ignition testing procedures for your motor along with all the other things you need to know
You can look at the parts online and compare to other motors but I do not think a 30 and 40 has the same CDI.