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After swearing up and down how happy i was with my trouble free 1991 yamaha 90hp precision blend motor it decided to kick back. after filling my tanks with fresh gas and topping of the oil resvoir, and taking a 15min ride she began pouring smoke, and end up loosing power.

i changed what seemed to be normal wearing plugs, and switched fuel tanks thinking maybe tank issues. cruised for 5mins or so near WOT in an effort to burn off whatever is there. no good and ended up stalling out, needing a tow back to the dock.

she'll start with high throttle settings, putting on a smoke show, if throttled back she stalls almost like she's been choked to death. however once running there is no power in gear and stalls almost as soon as you engage forward gear.

i was thinking maybe its not getting enough fuel, but getting correct amounts of oil per throttle setting (as its mix ratio is varied depending on throttle setting).

bypassed all fuel filters to rule out clogged filter. all filters appear free of debris. bypassed the fuel pump thinking that someone pumping like crazy on the primer ball may give some indication. if smoke lessens, it could be a bad fuel pump.

nothing - but really only looked for fuel shortage. could the oil pump be dumping extra oil into the carbs creating the smoke? or am i looking at a larger issue (guessing i am).

although i think i'll eventually take it to a mechanic would love to hear and thoughts of similar issues.

Thanks for any thoughts,

Dana

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I would conduct a cylinder leak down test (better than compression test) to make sure you didn't blow a head gasket. I would assume you could disconnect the oil injection and hook up a remote tank with mix in it to see how the engine performs.

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Sounds like a air leak in your fuel line somewhere. When the air laiden foamy fuel enters the VRO pump, it causes the pump to run rich on injecting oil, hence the smoke... I'd start by double checking all connections and looking for cracks, bad lines, perforations, etc. I had the same issue, to a lesser degree, and replacing all my fuel lines solved the problem.

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Dana,

The Oil pump is driven directly off the crank shaft. There are linkages to the carbs that regulate the amount of oil based on throttle setting. I have never messed with this but have looked at closely. I will look again today. With engine off, I would try to open and close the throttle assy and watch how all the linkage moves. If the linkage to the oil pump is not moving with the throttle. That could be it, something came loose. This is not something I would generally mess with :o

A simple compression test would also be a good idea for starters to be sure it is not something more serious. Stone cold I get 124 to 125 LBS on mine.

Update: Just looked at the shop manual... this can be the "control link rod" not clear on how it could go out of adjustment though... "If the rod is out of adjustment, an oil starvation condition could develop leading to premature wear and over heating. Incorrect adjustment of the link rod could also lead to excessive oil delivery resulting in a smoking power head, fouled spark plugs, or erratic performance" per page 5-25 in the Seloc shop manual.

Good luck

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thanks for the suggestions. i've tried some and will be taking the boat home where i have more tools before she heads to a real mechanic.

i disconnected the oil injection where the oil actually enters the carbs, rerouted the oil lines into a bucket. i then tried running the motor on a 50:1 mix thinking i may see reduction in smoke. was uneasy about running without the injection so only ran if for a couple short bursts. it was still smoking and could not keep it running.

when i get home i'll dive into the selco manual, and check compression. i hate to mess with the mechanics of the oiling system so will mostly read and look for obvious issues.

again thanks for all the help and i'll report back with my findings, if any!

dana