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503 Throttle Problem

in 2 Stroke Technical Questions 7 years ago
I have a problem with my Rotax 503, (dual carburetors, dual Ducati ignition). The Bing 54 carburetors are set up per the manual. Idle is about 2100 rpm. It's in a pusher configuration on my Chinook Plus II. When I advance the throttle from idle, the engine hesitates / stumbles and then catches up and runs fine in the mid and high ranges. When I close the throttle, bringing it back to idle the rpm drops 300-400rpm below the set idle speed and then slowly returns to 2100. Because this causes the engine to run very rough I often have to open the throttle slightly to get it back to the set idle speed. Does anyone have a clue as to what's going on? I've about run out of ideas, having rebuilt and re-tuned the carburetors trying richer and leaner e-clip settings for the needles as well as larger (50) and smaller (40) idle jets.

  • Re: 503 Throttle Problem

    by » 7 years ago

    Hi Scott...are you opening the throttle slowly or snapping it open.
    Is the choke/coldstart seating fully.

    Have you synchronised the carbs together?

    Nick.
      
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  • Re: 503 Throttle Problem

    by » 7 years ago

    Nick...thanks for the response. I have synchronized the carburetors and I'm opening the throttle smoothly but not snapping it forward, just as I would on take-off. Coming back to idle I've done it both slowly and chopping it. Either way, the rpm can drop as low as 900 or even stall out. I've noticed that if running richer (needles clipped at position 3 on a four position needle) that it will drop but not as far (to around 1500 rpm). One thing I have not checked is the seating on choke/enricheners. I'll do that next. If they're seating all the way I may try putting the needles in position 3 again and go to a size 50 idle jet to see what happens.

    Scott
      
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  • Re: 503 Throttle Problem

    by » 7 years ago

    My 503 dcdi is a pusher also on a trike...when I close my throttle in flight the revs drop to just above the ground idle speed and no more.
    My jetting is std...I have both std needles set one slot richer.

    What max RPM do you get on take off.

    Nick.
      
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  • Re: 503 Throttle Problem

    by » 7 years ago

    I've adjusted the prop to give me just under 6400 rpm (6340) at full throttle on take off.
      
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  • Re: 503 Throttle Problem

    by » 7 years ago

    Hi Scott...so is this a new problem....did it used to behave as it should...or is the aircraft new to you.

    I wonder if you have come across this guide.

    http://www.cps-parts.com/catalog/rtxpages/articles.php

    Scroll down to Comprehensive Guide To Troubleshooting

    Always seems to cover most things...some very good ariticals amongst that lot.

    We are away for Christmas now with family..

    Catch you in a few days...have a good Christmas.

    Nick.
      
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