Hi,just changed the oil and used synthetic,now it burns oil for a few minutes when first started,I checked breather and it is clean and dry no oil in it. Suspect valve stem oil seals or piston rings but surprised that I didn't burn oil previous to oil change,even tried dropping the oil level a little but still the same,anybody any ideas?
I have always had good luck using SAE 30 Briggs & Stratton small engine oil. It seems for me that the multi vis oils always tend to burn some in my small engines. I haven't found the need to use a synthetic oil in any of my equipment .
How many run time hours are on this motor? It may not be broken in yet.
Another cause is that most of these "smaller" engines that can frequently run with sustained, relatively heavy throttle loads do not have a valve seal on the exhaust valve stem. I just checked the EF3000iSE parts diagram and this engine intentionally does not have an exhaust valve stem seal. What that means is that after engine shut down the oil film on and above the exposed-to-oil valve stem can and will trickle down the valve stem running clearance into the exhaust port -and- dramatically be burned away inside the exhaust system on the next engine start-up. Less than 1, MAYBE 2 drops of oil will be lost . . . up in smoke . . . to the alarming dismay of the owner. This is not an anomaly. it is more indicative of full synthetic oil's superior boundary film lubrication dispersion ability, compared to the more inferior conventional oil. It is a very small price to pay for better longevity of the hard working Yamaha engine using full synthetic oil.
BTW, it does not smoke or burn oil when the engine has run a short while because the crankcase breather disc valve maintains a slightly negative atmospheric pressure in the crankcase (everywhere the engine oil is) to prevent oil leaks and minimize oil burning. You should also return the oil level to the full mark as it will make no difference in the smokey start-up.
While most people would agree that synthetic oil is superior to Dino oil , there are some things to note. Most of the synthetic oils on the market are designed for late model cars. Two ingredients that are very important to older cars with flat tappet cams which includes small engines are zddp (zinc) and phosphorus . These have been reduced greatly for the sake of the catalytic converters and other sensors on new cars. Oils that are made for small engines have these two anti wear items in higher quantitys. Small engines without oil filters have no way of removing the combustion by products other than changing the oil on a regular basis. Doesn't do any good to have an oil that lasts longer if it is full of dirt. All of the small engine manufacturers market oils that have the higher levels of wear additives. This is not to start an oil wars argument but to just show that car oils may not be the best for a small engine.