OK, wait one huge second. I think we have a different problem. If there is fuel on the butterflies, and some smoke, I would bet one or both of the injectors is sticking partially open. This is even more likely with the fact that this is an RV in that RVs often sit unused for extended periods of time. When you first turn the ignition on, the injectors pulse a little gas into the throttle body. There should be a mist that stops soon after turning on the key. If the injector drips after that, it is stuck. Try whacking the injector with the handle of your screw driver. You may even need to whack it, when the key is first turned on, to break it loose under power.
If you do not see a drip, and the fuel does mist when the key is first turned on, then I would go for electrical. Ignition coils can short out at the most opportune time. If the coil is partially shorted, you can probably get it to run temporarily by unbolting the coil from the engine and laying it on a piece of cardboard so it is electrically insulated from ground. I had this sort of thing bite me after an engine change in one of my Jeeps. I was sure I had not wired something correctly, but it turned out to be a partially shorted ignition coil. It would run for a short period and then die. I didn't find it, until I put an oscilloscope on the input of the coil. When coils short out, the normally short to the core, which is bolted to the engine. By unbolting it, you insulate the core, and it sort of works, or at least works well enough to conclude what is wrong.
IRV2
