08 yz450f running rough and oil problems

I'll start from the beginning. I bought this bike with less than 10 hours on it and it ran perfect. It is my first carbed vehicle so trouble shooting is a mystery to me right now.

I took her out on her maiden voyage with me a few weeks ago and I put her down on a rock just right to where I cracked the crank case cover. I didn't realize it until after riding it for another hour or so. When I got home o just let the oil drain out of it. Once I got the parts in to replace it I drained all of the oil then pulled the cover off. Then I put the new cover on with new gaskets. Then I replaced the oil filter and filled the bike up with oil. My riding buddy told me an amount to put in and it ended up being too much oil. WAY TOO MUCH. I ended up running it for a few minutes with a whole quart too much oil in it. While it was running with too much oil, it would hiccup under throttle almost like the fuel was cutting out. Then I let the bike sit for a few days until I had time to tackle it again.

Got back to the bike today and decided to just drain all the oil and refill it with the proper amount. I did that and let it run for a minute or too then rode it up the street in 1st and 2nd.. still runs like shit and it hiccups under throttle. Pulled back on the garage and shut it off. I went to check the oil while it was still warm and bubbly(maybe milky) oil came spewing out of the dipstick hole.

WHAT DID I DO? I'm sure I &%$#@!ed something up, I just don't know what.

The left side cover was broken. And I did the oil change correctly.... just doubled the oil amount on accident

If the left side was broken, there's a possibilty that the stator was damaged.  You could have an intermittent short or open working in there.  Another less expensive possibility to try first is a new plug.  With all the oil you had in it, yours could be partly fouled. 


As far as the bubbles and foam in the oil, you should check the oil after the engine has been run for at least a minute or so, and after you let it sit 30 seconds to settle.  Because the return pump that sends oil back to the "tank" in front of the engine outruns the feed side pump, and comes into the tank at a point below the normal oil level, it's normal for it to spit and blow bubbles into the tank.  Some oils also foam less and settle faster than others, too. 

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