Re: Please Help. Rear Engine Is Stumbling.
Another vote for fuel starvation. You have the classic signs.
I don't know where the blockage is, but I feel pretty confident that you have a fuel restriction. I had this exact issue on my bike and it required a thorough dissassembly and cleaning of the carb. I have also seen this exact behavior on numerous small engines (I used to work at an equipment rental, maintaining and repairing small engines) and it was pretty much always a lack of fuel.