I'm new to 4 strokes, a Merc 90hp '03 model. It starts and runs great,however when it idles for 10 minutes or so it starts to smoke, once you rev it up the smoke goes away. If I'm idling out it looks like a 2 stroke.
Normal or a problem in the making or just normal ? Oil level is steady, water pump working. Help!

You really need to have a tech check it out. It could be bad valve guide seals or it could be stuck rings. The rings are bad to stick on the four stroke 90's and 115's. You can run the snot out of it and unstick them or you can use ring free and mix one ounce with every 10 gallons of gas. I use the ring free everytime I put gas in mine.

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I've spent most of my life fishing.....the rest I've wasted. Lifes too short to only fish on weekends.

I'll pick some up and give it a try
Thansk for the info

Are you sure it isn't steam from the exhaust? With the cooler water temps my 4 stroke will emit steam while idling.

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Shellback CVA 59 VF-74

It smells like oil and doesn't disapate like steam, plus I've noticed it during the warm weather. So probably oil :-(

Hmm, if the oil is not going down...and you seem to see it burning off that means its being replaced some how. Most likely with Fuel.

It could be that the engine is running too cold....and the fuel is thinning out the oil.

TMD

Exactly right....if your rings stick your oil level will come up because you are getting some fuel in the oil. Thats why Yamaha recomends using ring free in their 4 strokes.

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I've spent most of my life fishing.....the rest I've wasted. Lifes too short to only fish on weekends.

Looks like it's time for some Ring Free.
Thanks for the info!!