Hi guys, when I start my 503 dcdi the pto egt lags behind the mar end and gives no reading for maybe 20secs or till I open the throttle a bit more,

I was thinking the maybe the idle mixture for the pto carb maybe set to weak...or could it be that the mag end is to rich....anyway what the best way to synchronize them,

At the moment I just have them both out approx 3/4 turn,

Its a quite new engine and carb set-up with about 20 hours on it,

I have the carbs balanced as well as I can get them after setting them with a manometer,

The EGTs at higher revs are quite well matched....the engine is a bit lumpy at idle which is a tad over 2000rpm but smooths out over 2500rpm.

  • Re: 503 dc idle fuel mixture adjustment

    by » 13 years ago

    Hi Nick,

    Bing says that the idle air screw should be 1/2 turn out. I'd try that first. Ideally ( although it is kinda dangerous) you should warm up the engine, turn each idle air screw out from its standard setting slowly with the engine running at idle. As you turn the screw out, the engine should begin to idle faster or run rougher. If it runs rougher, turn the screw in until the engine begins to run faster. Keep turning until it begins to slow down again then back the screw back out to that sweet spot. If it runs faster as you back the screw out, keep going until it begins to get rough, then turn it back in to the sweet spot. Then do the other carb the same way.

    This will not affect the midrange or high end mixture settings, or the balance, as the idle circuit is no longer a factor once you go above 2000/25000rpm.

    I had a 582 that did the same thing. It would run on one cylinder for 10 or 20 seconds at startup. Did make it idle better but never cured it completely of the startup thing.

    Good luck,


  • Re: 503 dc idle fuel mixture adjustment

    by » 13 years ago

    Many thanks Bill...I will have a dabble.


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