Yes this can be an issue with inverted. My Magnum 70FS isn't having this problem but the OS46 2 stroke I had in it did. What I did was leave the high speed screw closed until I put the starter to it and closed it first when landed. It will also need a different setting than normal. What I found is the screw didn't need to be adjusted out as far when mounted inverted and it was still running rich as it should (not to lean). I did not move the tank as many suggest and it worked fine doing this. Only reason I changed from the 2 stroke setup was I wanted the four stroke power. I know where your at though cause it drove me crazy until I figured out the practice listed above. Once i had it out a couple of times I did talk with a couple of people who had been down the same road and amazingly they all said they did the same thing rather than altering the tank placement.