[Christ]

Well, fuel density, in this case, refers to BTU/volume. Incorrect terminology haunts me, sorry.

I understand what you're saying though, and even that is a correct reasoning for stumbling - The fuel might not be vaporized as much, thusly making it more liquid than vaporous, and causing stumbling due to the "lean" condition created therein. (Liquid fuel does not burn effectively, causing less surface area to consider for the fuel/air mixture, making it "lean") At least iirc, that's true.

However, if that were the case, adding Xylene/Toluene to fuel would raise it's specific gravity as a solution, which might also throw off the A/F ratio... which didn't happen in my case, at least not according to an A/F meter on a standard (non wide band) O2 sensor. It stayed in the same place before and after adding Xylene to the mix.

For corrective purposes, however, yes, I meant BTU/volume in that reply.