Dave;
You might try looking at both choke cables. Have someone pull out the choke
cable, then look at each carb, to check that each choke arm is going to the
stop. Sometimes one of the choke cables over time, will slip a little. When
this happens, one side of engine will get a choke and the other side only
partial choke or none at all.
Jim Brown
David DeFord wrote:
>
> When it was new, our 912S started as prescribed by Rotax when cold, i.e.,
> full choke with throttle fully closed. Opening the throttle even slightly
> would kill the engine, whenever the choke was applied. Over time (400
> hours), it began to need just a bit of throttle along with the choke, in
> order to start. Now it runs very roughly on a cold start with full choke,
> and will die after a few seconds of this (if we can stand it) unless the
> throttle is opened more than 1/4 inch. It then runs perfectly smoothly,
> from idle to full throttle, without the choke. Unfortunately, opening the
> throttle this much causes the shaking to become so violent (momentarily,
> until it becomes suddenly smooth) that it typically dislodges the muffler
> from exhaust header pipes. It starts just fine without the choke, once it
> is warm.
>
> Please don't bother to suggest balancing the carburetors, which we have done
> very precisely (witness the very smooth running without the choke). We have
> partially disassembled the carburetors and cleaned all of the jets with carb
> cleaner (though there was no sign of any contamination or blockage). Mag
> drop on both sides is fine, compression is like new, and we have never
> experienced any kickback on starting. We have searched in vain for any
> vacuum leaks, and the float needles seem to be keeping the float bowls
> filled properly.
>
> We feel that we have exhausted all of the reasonable possibilities, and so
> are open to bizarre and unlikely suggestions as well at this point!
>
> Dave DeFord
> N135TD (monowheel XS, 912S, Airmaster)
>
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