Do a compression test.

I still think you are running on one cylinder and the fuel isn't being burnt therefore contaminating your oil.

 

I made a compression test and both sides shows similar values. It also made an much better and smoother noice after I made the test and got the spark plug cables back on the correct way so it feels like it is running on 2 cylinders now. It also got a lot more powerful.

Is it common that there is no color to the oil even for a few hours? I mean if I change the oil in my car it immediately gets black on the oil stick after I start the car.

 

When I change the engine oil and filter in my truck the oil stays new looking for 100’s of miles easy…. Maybe you’re not getting all the old oil out….. or maybe it’s a very dirty engine…don’t know… but I have no engines that will turn new engine oil black right away.

 

My Ford F150 with over 250,000 miles has the oil a little darker at oil change than when it goes in, but it is still clear, just darker. I change my oil and filter every 3000 miles. Even my old Triumphs only darken the oil between changes and the clutch runs in the same oil as the engine. Now my Honda VT1100 will make the oil black in 2500 miles, but the oil lubes the engine, clutch and transmission. The transmission is harder on the oil than either the engine or clutch.

As to the gas smell? Maybe you just don't run it long enough to get the oil hot enough to evaporate any gas that has contaminated the oil?

 

Tip: many machines don’t have the oil drain plug ideally located to get ALL the old oil out, that’s when my OCD kicks in and I tilt the machine towards the drain while it’s hot and draining to get it all out. If you do this, you must be prepared to add more oil than the book calls for to reach full mark. My truck calls for 5qts with filter, after I tilt it over toward passenger side where the drain is, I get another 3/4 qt out, so I add nearly 6 qts to bring to full mark.

 

It could be the case. I usuly only run the machine for shorter periods, maybe it´s not hot enough to burn the gas in the oil.

If I listen to the sound it makes while idle it actually sounds like it is not running on both cylinders all the time. It sounds like it skips a stroke once in a while but I dont know if it is normal. Both sparkplugs looks good. It is difficult to compare the sound from videos I find...

 

Post up a vid. 800s in particular have a sound that would make you think something is wrong with the engine.

I change the oil in the wheelers every 50hrs and never had the oil in the 800 or any of them come out black, always goldish.