RE: More Rio 51 woes.
The connector is for an optional kill switch, or a failsafe equipped kill switch, be carefull, as you found out it will bite!! Mine runs ok, nothing special but ok. Use a business card to set your 'air gap' , the spacing between coil and flywheel. I took over 3 hours to finally get mine to fire for the 1st time. I am at 400 feet obove sea level and I had to set my low speed needle to 1 1/2 turns and high speed to 1 1/4 turns just to get it to fire. I am currently at 1 1/2 on the low end and 1 1/8 on the high but the most I can get out of it according to the little GPS unit is 25 mph, I tried to lean it out a hair more and it just got hot and dropped .5 mph. I really think these are just real finnicky about the needle settings, I tried to richen the low end up 1/8 turn and it would not start at all, went back to 1 1/2 and it fired in 4 or 5 pulls, but it is still def not a ZEN. I would have to suggest you try to return at least the engine and try another one, or possibly try getting a different boat or replace engine with a zen. I am almost ready to just bite the bullet and buy a MOD 5 ZEN from WHH. I do really like the hull though, I have yet to dump it over and I have seen a bunch of cats and unlimited styles flip a lot so I am sticking to this HULL but i am almost done with the fugi. I really hope you can either get her started or return the engine for a new one.
Hairball