Yamaha Enduro 40 hp 2 stroke smokes a lot

[kurakura]

Hello, I have recently purchased 2 Yamaha Enduro 40 hp electro start and remote control for my 50 feet sailing catamaran (now with about 100 hrs. of use). They are located in boxes to minimize the noise and the weather exposure. When I start them, they smoke a lot and if the boxes are closed it seems that the smoke soffocates the breath of the engines and they stop. I use yamalube 50:1 but seems to be too much. I check the spark plugs and they look black and oily. I don´t let them running on tickover for more than 2 minutes but the problem persist. I never use them at full throtle so, can I reduce the mixing rate to 40:1? Does it help? If I leave the boxes open they don't stop but they produce a lot of white/blue smoke. They work perfectly when I give more throtle. I use original spark plugs. Where is the problem?
Another problem: In choppy conditions lets say 1 meter waves or more, when the back of the boat sinks on a wave, the engines stop. Is the water level flood any air intake that causes the problem. They start inmediatelly.
Thanks for your help.

[boats.net]

Running engines in an enclosed well will make them run rich if they are running on their own exhaust even most of the exhaust goes thru prop, exhaust will come out the exhaust relief holes which are above water line. If the water in the motor well gets high enough to cover exhaust relief holes then the engine will smother out and shut off. Don't have any information on Enduro motors but the 40 US motors are 50:1 mixture and I wouldn't recommend leaning out oil mixture

[Ken]

boats.net,
I thought Yamaha stopped making pre-mix motors back in 2000 - is it possible "kurakura" has oil-injected motors and he is still adding oil to the fuel like you do during breakin?
Ken K

[boats.net]

Ken
2002 there was 40,50 and 130hp available in non oil injection but not sure about the European motors but I think they still sell non oiler's and I think most of their Enduro models are non oiler's but I could be wrong.

[Ray]

they still sell enduros(sp). i have recently acquired 2 2004 200hp pre mix motors. anyone have any idea if parts (rings and bearings and such) are available in the usa.
Ray

[boats.net]

Ray
Is there any model numbers at all on the transom bracket to identify the motors? Clive from Wales sent me 1994-2002 Yamaha parts disk and the model numbers on disk are the same as the motors here in USA.

[Ray]

it would appear that the motors are 2002 the #s are
200 AET from what i was able to find out on the net is, A denotes it as 2002 , E for enduro T for high thrust. this is on the serial # tag

Ray

[kurakura]

Thanks for your comments.
Boats.net, Intersting suggestion! I think that the smoke exhaust must be located over water level (for that reason the box is full of smoke) and could be the reason why the engines stop when the water level rises, actually I run the boat slowly to reduce the sinking of the engines deep into water after passing waves.

This yamaha enduro 40 hp is the old model that you can still buy in Indonesia (where the boat is located) and for sure is a pre-mix model. New models doesen´t fit in the "box" without making structure modifications, they are very strong, last owner use a pair of them during 8 years without any problems, for that reason I have bought the same ones.
Can I run them with a 1:60 or 1:70 mix Yamalube?, I run them at 75-80% of the maximun power. Will this reduce the smoke?