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Rough running 912ULS 2500-3000 rpm

in 912 / 914 Technical Questions 13 years ago
Hi, I am having rough running in the 2500-3000 rpm range on my 912 uls.

the carbs have been cleaned, new carb o-rings installed thu-out. idle mixture screws are at 1 1/2 turns out.

I synced carbs with carbmate at 3500 rpm, below and above the 2500-3000 rpm rough range everything is fine.

I am thinking of dropping my carb needles to position # 2 (leaner) , currently they are in position #3. I am just a little leary of being too lean, thoughts ?

  • Re: Rough running 912ULS 2500-3000 rpm

    by » 13 years ago

    Hi Kevin,

    If you synced your carbs at 3500+ rpm then it is very normal for them to be out some in the 2500-3000 range. Don't worry about it there. You spend almost all your time at idle or cruise and that is where it is important to be synced. You will not get them dead on sync from idle all the way through 5000+rpm. There will be that spot down low when the carbs are coming off idle and start to leave the idle circuit and transfer more towards the main jet and needle side. Once the balance tube is reconnected that will help some. Sync at idle and 3500+ and and go fly. I rarely change needle clip positions and there should be a good reason to do so plus the correct gauges to monitor the engine.

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

      
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  • Re: Rough running 912ULS 2500-3000 rpm

    by » 13 years ago

    Hi Roger,

    My engine is running rough, shakeing/not smooth at rpms between 2500 to 3000. This is on the ground and in the air. It is rough at that rpm range no matter what I'm doing , ground testing, carb syncing, or pulling throttle on final is the one that especially bothers me. The carbs are synced for 3500 and everything is running smooth above and below the 2500-3000 rpm rough range.

    I am thinking that the 2500-3000 rpm range is where the idle circuit stops and the mid range/ needle becomes a factor, is this correct ? I am thinking at full throttle that the needle does not have much bearing on things, am I thinking correct ?

    I recently have changed to 3 blade Inflight adjustable prop, I can change my temps quite a bit just how I set the prop.
    The engine is monitored by a Dynon d-120, with oil, 2 cht's, 4 egt's , coolant temp and manifold pressure.

    On my last flight
    OAT 40F ,3500ASL,
    at cruise 5080 rpm 25.5 INHG ,
    oil was 206F (with 2/3 oil cooler taped) .
    CHT's #2=190F #3=195F
    EGT's #1=1341F #2=1364F #3=1311F #4=1369F
    coolant is measured 14" from expansion tank on way to rad in and was 171F ( I was also running my cockpit heater which uses coolant) 50/50 mix coolant

    I know what the max temps are for cht and egt, rotax is good with letting you know those.

    What I would like to know is what is the normal average running temps. The numbers I list above are about the most even I can produce with changing prop pitch. If I thin the prop my egt's drop on my front 2 cylinders to 1200 to 1250. rear two go up slightly

    I think I have some room to try a needle position change from position 3 to position 2, what do you think? can I do damage ?
    I would like to cure the roughness but not cause other problems, Thanks Kevin
      
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  • Re: Rough running 912ULS 2500-3000 rpm

    by » 13 years ago

    Hi,
    I decided to drop the jet needles one position , from cir-clip position 3 to position 2.(leaner)
    I programmed the Dynon D-120 EMS to give visual and audio warnings if egt's went over 1520F.
    The rough running that I have had in the 2500-3000rpm range is gone.
    I verified the carb sync and then went flying.
    I had higher egt's for the front two cylinders on climb (1420F range) rears1360F

    In cruise my numbers are:

    conditions OAT 2C Dewpoint -2C 3500ASL

    cruise rpm 5070 MAP 25.3 INHG

    Oil temp = 178F (with no tape on oil cooler)

    CHT's #2 cylinder 193F #3 cylinder 197F

    Egt's #1 = 1358 #2 = 1386 #3 = 1372 #4 = 1378

    coolant temp 171F

    I am pleased with these numbers and the way the engine is smooth throughout its range, I will be watching the temps closely , but so far it looks good
      
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  • Re: Rough running 912ULS 2500-3000 rpm

    by » 13 years ago

    Hi Kevin,

    Looks like you took a step in the right direction. Now try that piece of 2" aluminum tape across the oil radiator to get the oil up a little higher for the winter months..

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

      
    Report

  • Re: Rough running 912ULS 2500-3000 rpm

    by » 13 years ago

    Hello Kevin
    Sounds like things are pretty well right on except you should probably get the oil closer to 200F. Mine is taped up quite a bit,runs up to 220 on climb out and settles at 200 at cruise.The Thermobob holds 180F on all configurations.
    How`s that new prop working out? I suppose you see 1500FPM quite often in this cool air.
    Cheers
    Don
    Thank you said by: Kevin Machniak
      
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