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Hi all,

I recently became the owner of a 912UL on a GTE912 trike. The 2001 vintage 912 has 232 hours so it has spent a lot of time sitting.

The long story follows but the question is why does the idle mixture screw on the 2,4 side need to be closed on this engine for a smooth idle (1800 rpm)?

Thanks in advance for any responses or suggestions.

History -

To bring it back to a safe flying condition. I did the rubber replacement items, new fluids, new sparkplugs, carb rebuilds, etc.

Initially, the plugs from the 1,3 side came out with tan coloration. The 2,4 side were glossy black.

After all maintenance items were done, an engine runup was performed, compression checked good and the carbs balanced. The engine ran smoothly above idle but shook quite a bit at idle (1800 rpm).

After various checks, it was discovered that idle would smooth out if the 2,4 idle mixture screw was turned all the way in???

The bowl was removed, fuel level checked and the idle jet and idle mixture screw was checked - all ok. Eventually the idle jet and mixture screw was swapped to the other carb - no change. Also, the fitting and direction of the "choke" was checked - again, it was ok.

I hope to get to get to the bottom of this problem but I am stumped at the moment.

Thanks again,
Charles
  • Re: 912UL Carb idle mixture

    by » 11 years ago


    2-4 carb is too rich:
    -Is the float valve is leaking: Carefully remove the bowls and check that the fuel level is equal on both bowls.
    -Or is the slide miss-indexed? look through the intake side: the slide should be perfectly orientated in the throat.
    -Needles are set at the same clip position?
    -Plugged atomizer port?
    Anyone else run into this?
    Rob

  • Re: 912UL Carb idle mixture

    by » 11 years ago


    Rob

    I have check the bowl fuel level three times now. Each time it is at the presribed height in each bowl.
    Slides are indexed properly (checked - not assumed)
    Needles are clipped at 3rd position from the top
    Not sure what the atomizer port is - if it is the opening in the center of the carb front where the filter attaches - then it is clear

    Thanks for taking the time to respond. I will recheck the atomizer port.

    Charles

  • Re: 912UL Carb idle mixture

    by » 11 years ago


    yes, the two atomizer ports are in the flange that the filter clamps onto. One goes to the idle side (has a brass insert at the opening) and the large one goes to the mainjet. remove the jets and blow out any contamination. double check your idle jet with flashlight; it has lots of hiding spots for contamination.

  • Re: 912UL Carb idle mixture

    by » 11 years ago


    Rob,

    I want to thank you for the suggestion to clean the atomizer ports. I had cleaned the carb body during overhaul but did not specifically check that orifice. I cleaned it, returned the idle mixture screw to 1.5 turns and all is well.

    Thanks again,
    Charles

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