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Hi guys, let me know what you think about the following issue.

On throttling up engine hesitates, doesn’t build rpm for a moment and then catches up. A very noticeable lag of the rpm following the throttle movement, the sharper the bigger.

4000rpm Mag checks:
Mag 1 off 200-300 rpm drop. Seems to be 200 when engine is warmer, reaches 400 for a moment on colder(just above 50C oil). Saw the engine cough/misfire during the first check on colder engine. This results in a short additional drop in rpm - more than 400-500 and running unstable. Didn't happen on following tests that day.
Mag 2 off - rpm drop of 400-500 rpm, running stable.

Swapped the ignition box white connectors to check for change:

Vertical connectors swap:
Mag 1 off: drop 500-700rpm
Mag 2 off: drop 150-200rpm

Horizontal connectors swap:
Mag 1 off: drop 500-700rpm
Mag2 off: drop 150-200 rpm

Changed the spark plugs, no difference.

  • Re: 914 throttle lag, mag rpm drop

    by » 3 months ago


    Hello Emil

    I have seen this on the type 914 before.  Normally it just needs a bit more fuel in the 4000 RPM range.  (needle adjustment) The high mag drop suggests a lean burn so move the needle clip one position to enrich the mixture and try it again.  Not all 914 need this but the high mag drop suggests your engine does.  Overall running will not change but the hesitation should improve.  

    Cheers 


  • Re: 914 throttle lag, mag rpm drop

    by » 3 months ago


    I moved the 2-4 carburettor needle one position richer and the mag drop improved. Thanks for the help on that!

    However, there's still that lag when throttling up sharply from lower rpm(2000). Not that noticable if you throttle up above 3000rpm. Tried adjusting the idle mixture but didn't notice difference.


  • Re: 914 throttle lag, mag rpm drop

    by » 3 months ago


    The lag in throttle response may not be the engine, but your throttle system. Double check this to rule it in or out.


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


  • Re: 914 throttle lag, mag rpm drop

    by » 3 months ago


    Emil Lomliev wrote:

    I moved the 2-4 carburettor needle one position richer and the mag drop improved. Thanks for the help on that!

    However, there's still that lag when throttling up sharply from lower rpm(2000). Not that noticable if you throttle up above 3000rpm. Tried adjusting the idle mixture but didn't notice difference.

    Advancing the throttle up sharply will definitely produce a lag in response! This is normal as the Bing carbs don't have an accelerator pump to pour more fuel in. Also, a turbo takes a while to spool up when first applying power. I have a turbo in my car and it definitely accelerates faster if I slowly advance the throttle. 


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