Like others said, too much fuel in the engine when starting will do that. Pull or pinch off the fuel line next time, then let it run off the fuel in the crankcase. Often, just before the engine dies, it will kick off in the correct direction for a couple of seconds and sound much happier when it does. You can often release the fuel line just at that point and off she goes, a technique I use when I've pulled too much fuel in during choking, but not I guess entirely recommended by the safety committee. A better tactic is to go easy on the priming/choking. You can simply pull off the line (and the muffler pressure line too unless you want to bath the model in fuel, or plug the fuel line) and hit the engine with the starter to let it burn off the excess, don't worry which way it is running at that point, just let it burn up fuel.

Once/if you get the engine idling, try pinching the fuel line to see if and how much the rpm increases before it starves.. you can release it before it dies. A small increase is okay, but if it speeds up notably then your idle mixture is too rich fer shure. Lean it a bit at a time . A clue is the transition from idle to high throttle - with plug heat off. Too rich and the engine will stumble when you advance the throttle. The idle needs to be towards the lean side, so that the rpm only jumps a little with the pinch test. A too rich idle does no good at all. The engine is not producing a lot of heat at idle but remember that by leaning out I don't mean going too far, but just to the point where it runs and transitions cleanly. If the engine dies quickly when you pinch the line then you have gone too far [okay, I see the Evo 46 has an idle mixture limit too - if so you're not going to go too far]. Ideally (ideally to me.. others may differ) if you pinch the line, the rpm should increase just a wee bit, and after about two seconds or so the engine should start starving for fuel. You should do all this after setting the top end correctly, then check the top end once more afterwards.

I found these comments from a reviewer:

"The engine started easily and was running very rich. It took nearly a full turn of the high needle to get it running from a four-stroke note to a rich 2-stroke. On the low end, the engine wouldn’t accelerate well when advancing the throttle. Even when advancing the throttle slowly, the engine would stumble and then stall. Making an adjustment to the low-end screw had a positive and dramatic impact. The engine was running extremely well. Even with the high-speed needle turned all the way in (lean) against the limiter, the engine was still a little rich. Since this was the first flight it was decided to leave the mixture slightly rich. If it remains rich in subsequent flights, the limiter can be readjusted to allow the engine to run leaner."

Don't go too far on a pusher airboat, stay comfortably away from peak rpm when setting the needle. Sounds like the built in limit is a good thing.

A 9-6 is not going to hurt your .46, but it is on the small side for your application and a prop with more disc area and perhaps finer pitch is going to perform better. For an airboat you have a lot of load and the top speed is not high enough to warrant a prop running at a pitch speed of 100 mph+. A 10-6 pusher is as mentioned a better choice. If you could find an 11-5 pusher even better, but I don't think there is one. Master Airscrew has a 10-6 pusher, APC makes 10-6 and 11-6; In truth, since a smaller prop runs cooler the 10-6 may be the better choice from that standpoint, but for the airboat if it fits, the 11-6 may work really well too. Perhaps try that after getting some running time on the 10-6.

In terms of running up your engine static, to tune it, test throttle transition etc., personally I would recommend fitting it with the tractor (normal) prop of the same size as your pusher - that way you get all the time in the world to set it up with no fear of overheating due to lack of forward speed, and you can spend a whole tank full of fuel tinkering if you choose to or need to.

MJD