I received my rebuilt carbies from the local Australian Rotax dealer a few months ago, and have never been able to get the carbies to balance properly since, either rough running at idle, or rough in a RPM band around 4500 to 4800, i have never been happy with it.

This weekend i attempted to rebalance the carbies again for the 3rd time, this time i noticed something i haven't noticed before.
All this has been done by the Rotax manuals, and videos, just to make sure i was doing it correctly, which i am.

the issue is best shown in pics..

with the throttle spring removed, the idle stop is set with the feeler gauges as per the manual and video. throttle in cabin is set to idle, springs reattached to the carbies, and cables set, (i have done this with throttle at full open and idle positions, nothing changes but the distance between the idle stop after tightening everything up.

As you can see from the pictures, when idlt screw is set with the feeler gauges, the thread lengths are different, by approx 2 to 3 threads.

when adjusted at the other extreme, to ensure idle stops are the same, then the same difference occurs at the full open position, with there being about 1 to 2 mm difference in travel.

My question is this, is this a throttle system rigging issue, or an internal carby issue, with the carbies having different throttle valve movement angles? and how can this be fixed?

Thanks in advance, Rob.
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  • Re: Carby balance issue

    by » 6 years ago

    The idle stop screws can be a different lengths. Your idle stop plate could be bent slightly. If it was bent you could tweak it back with a pair of pliers. You don't really care what the screw length is just make sure the carbs are adjusted the same with the feeler gauge and then pneumatic sync from there.

    Roger Lee
    LSRM-A & Rotax Instructor & Rotax IRC
    Tucson, AZ Ryan Airfield (KRYN)
    520-349-7056 Cell

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