03 yamaha rough idle and blue smoke

"I'm new to the forum and

"I'm new to the forum and fairly new to boat ownership in general. I recently bought a boat with an '03 yamaha 75 hp 4 stroke. I had carb problems (engine wouldn't idle - and eventually wouldn't start) after storing it for the winter. I had the carbs overhauled at a local shop and after the repair I drained the gas and replaced the fuel filter. I've had the boat out a couple of times now since the carb overhaul. The motor runs great when wide open but not so great when I come down to idle speed while still under power. It doesn't die on me but you can definitely tell the motor is shaking and struggling like it's about to quit. However, when I put it in neutral the motor smooths out and idles fairly well. To add to my concern, as I jump into and out of gear as I idle from crab pot to crab pot I start to smell oil burning and see blue smoke in the exhaust. In fact, when I give it a quick burst of gas to get around a pot the motor disappears in a cloud of smoke and my passengers cover their noses with their shirt sleeves. If I give it full throttle and zip down the bay at top speed I don't see or smell any oil burning. I come back to idle and putt around for a bit and then I get the smoke and smell of oil burning again. So after all this: At low rpm is there a chance that oil is leaking from the valves or rings - a quick run burns it off - only to accumulate again at low rpm? Or am I burning oil at all speeds and will probably need to re-build the head? A carb overhaul wouldn't be connected to this problem would it? Thanks in advance for any of your insight/advice."

"You are most likely correct.

"You are most likely correct. Valve issue with the blue smoke. Check compression. It is not likely that the compression is bad given it runs well at WOT. That will tell you if you have a valve guide or seal issue or some other problem. Whatever it is, blue smoke is not good on a 4 stroke. My guess is also that the problems are unrelated as far as the idle goes, unless you have low compression somewhere. If I read your post correctly the boat has never idled well before or after the carbs were rebuilt. Could be a vaccuum related issue or the carbs were not cleaned out all the way. Also could just be an adjustment. The best way to solve these problems is to eliminate as many things as you can, things that are definatley not the problem. Check your plugs as well, alot of times the color and carbon can tell you alot about what the fuel burn condition is like. If it were my motor I would check compression first and then make it idle well. Then you can check to see how the oil is making it into the combustion chamber. Good luck."

Thanks for the reply. I think

Thanks for the reply. I think I found the problem to the blue smoke. I also had the oil changed when the carb was overhauled...turns out the tech overfilled the oil by about 1/2 - 3/4 of a quart (the oil was registering way beyond the hash marks on the stick). I drained the excess off and took it out for a day of play at the lake - after an hour or so of starts and stops the smoke stopped and the motor seemed to idle better (both in neutral and under a load). So now my next question: will running the motor with too much oil (even for the two trips I had it out) do any long term harm to the engine?

"Too much oil should not harm

"Too much oil should not harm the engine. I dont know your motor in detail but I do know plenty of others and I have never heard of too much oil being harmful to the motor. Too much oil will foul the plugs I would change them to be safe, your motor will idle better assuminig they are fouled now. Its easy and cheap. I change plugs in most of my older 2 strokes a couple times a season depending (i have a couple antiques i still use). Too little oil in the fuel will definatly damage your motor. After I thought about it I forgot to mention it could be a resevour or oil pump issue. Glad it was a simple issue, most problems are."