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912UL 80 hp carb needle setting.

in 912 / 914 Technical Questions 12 years ago
My Rans S6-116 continues to be thirsty, at 4700 rpm and true 85 mph it uses ~13 1/2 L/hour.
I've no EGT fitted but CHT shows 180F. The water radiator is always half blanked and water always runs cool too ~160 F.

Can I lower the nearly new (25 hours old) needles each one notch 'leaner' than the book figure and carefully test fly watching how CHT performs without EGT and naturally eventually L/hour ?

mike hallam

  • Re: 912UL 80 hp carb needle setting.

    by » 12 years ago

    Hi Mike,

    Your fuel usage of 13.5 l/hr (or 3.5 gph) is perfectly normal for that rpm. I would not adjust the carb needle. Many fuel flow sensors are not spot on the mark either and others need to be adjusted to be accurate. You should also be running that 912 at 5000+ rpm in cruise. It wasn't designed to run in the mid 4000's for extended times and normal cruise.

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

      
    Report

  • Re: 912UL 80 hp carb needle setting.

    by » 12 years ago

    Thanks Roger, and I'll certainly not change anything yet to make it leaner in the UK winter.

    However the Rotax "One size fits all" guidance does mean she runs far too cool in the temperate summer period and at least on the thirstier side than others around here "tell".
    With at least 1/2 the water radiator blanked off the whole year round the water struggles to reach the lowest recommended 180F.

    Thus I'd like to hear from anyone who has tried dropping the needle one notch & its effects on consumption and CHT etc. ?

    I can't believe that such a small deviation will ruin the motor ?? OR does it ??

    Lastly RPM, I haven't met anyone with 80 or 100 h.p who runs over 5,000. I'm willing to give it a try, but most folk appear to use the low 4,000's
    So though it might not be your take, have you actually in a past life tried variations, or did you stick to the book and never find out what happens if you diverge ?

    Happy Christmas,
    mike Hallam.
      
    Report

  • Re: 912UL 80 hp carb needle setting.

    by » 12 years ago

    Hi Mike,

    If your EGT's, oil temp and CHT's are too cool especially in the summer then you could raise the clip to the #2 spot. That will lower the needle and make it run a tad warmer. It should be around 80F higher for the EGT side and around 20-25F higher for the oil and CHT's. When you do it the first time keep a close eye on the temps for the first couple of runs. Moving to the #2 clip position should not be a big deal if all the engine parameters show it is running too rich with your particular engine installation.


    Running too low a cruise rpm may be another reason your temps are too low.
    The engine was not designed to run in the 4000's and if you have a ground adjustable prop set it up to see at least 5500 rpm WOT flat and level and then run at least 5000+ rpm for cruise. The people that really know this engine will usually cruise between 5000-5400 rpm. I usually cruise around 5200 and for me that's around 115 knots. It was designed so you could run at 5500 for the life of the engine. Make sure you do a pneumatic carb sync every 100 hrs. or annual if it comes first.
    No matter what the other guys do at 4000's don't be sucked in.

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

    Thank you said by: mike hallam
      
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  • Re: 912UL 80 hp carb needle setting.

    by » 12 years ago

    Slightly off topic but since it has been brought up, running at lower rpm's, Say 4000-4500 rpm. This was a topic brought up last year at a different sight. One of the main Rotax repair stations said that there was no problem running at those rpm's for even extended periods. If a high performance motorcycle can run at race rpm and yet still run at residential speeds for days, why is it that I can't cruise at 4000 rpm. All engine operating parameters being normal, what's the reason?
      
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  • Re: 912UL 80 hp carb needle setting.

    by » 12 years ago

    Hi Kurt,

    It becomes apples and oranges. It solely depends on the engine Mfg and how the engine was designed.

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

      
    Report
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