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912/skydrive carb heat - carb ice??

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  • 912/skydrive carb heat - carb ice??

    Hello everybody,

    I have an AutoGyro MT03 gyroplane which has a Rotax 912 motor and carb heating which I believe is from Skydrive.

    I flew on Saturday but as anyone who tried to fly around Chiltern park it was a miserable day with fog lifting to low cloud and high humidity.

    I was in the circuit and found the oil temperature a little low so decided to land and add some tape to the cooler to try and bring that up before going for a longer flight. On the downwind leg I had a small vibration and once taxi'ing back in the motor was running on two cylinders. Which eventually cleared prior to shutting down. I added tape and did a couple of circuits to test but despite CHT over +100 and oil temp circa the same I felt it seemed to develop vibration on lower power setting (4000rpm) at approx 800ft AGL.

    So I decided to call it a day. Whilst taxiing back again the motor was in 2 cyl. It did clear but it was definitely not happy initially despite temps looking reasonable.

    One thing I did notice was that (as seated in the machine) the right hand water jacket to the carb was cool whilst the left one hot..

    Anyone had any similar experience? Could it be an air lock maybe??

    Thanks Phil

  • #2
    912/skydrive carb heat - carb ice??

    Are the water jackets plumbed in as series or parallel? If parallel there may be a kink in one hose and not the other(or similar obstruction), or some part of either hose is above the level of the radiator filler cap and therefore has an air lock.

    If in series, again look for the air lock possibility. Or an over tight cable tie.

    Can you post a link to some pictures of the install?

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    • #3
      912/skydrive carb heat - carb ice??

      Hi - thanks for the thoughts.

      I've asked an engineer to take a look but given the Gyroplane community is relatively tiny I wondered if there was any common issues apparent with BMAA pilots.

      I'm not near the machine so can't get a picture but the heating is done in series with the cross hose lying over the top of the outlet hose. Also the coolant wasn't just recently changed and I wonder if the system has got an airlock.

      Edited to add:- The engineer has had a look and can't find any issue with the carb heating and he even looked at the floats and set up and all is well there too. So I can only assume that I need to blank the coolers more (given it did seem that there was definitely something that was cooling the right carb on Saturday), although I do find that this motor cools remarkably when on part throttle - i.e. downwind, in the cruise, etc.

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      • #4
        912/skydrive carb heat - carb ice??

        I've just had the same problem with a Quik 912s 12 months old but built using the old engine out of my previous Quik 400 hours 2004.
        I'm quite an accomplished automotive engineer building racing motorcycle engines for over 30 years,so my standard is "perfection"
        It happened to me on a cruise decent,I dropped the revs to 2,500 for 30 seconds,tried to power back up and it just ran on 2 cylinders of the port side.
        I landed and the starboard carb had flooded with a little water droplet in both carbs. I stripped the carbs and carb heaters down to the last component part,but found nothing,cut open every fuel pipe and water pipe on the aircraft looking for any imperfections.....but found nothing. I took the carbs off the wife's Quik and stripped them to compare......but nothing.
        I measured everything and compared it to Rotax and bing manuals.....all measurements perfect. Even left the gloats soaking in fuel for a week just to see if one was pourus......all perfect !

        It would seem the fuel float needles have a spring inside them, Rotax have changed the strength of these springs 3 times in the last 10 years due to carb flooding issues due to the shaking of the engines on low tickover and poorly balanced carbs.

        I've raised the tickover on idle from 1600 to 1750 and it has made a fantastic difference to how smooth the engine now is. I also balanced the carbs to perfection at 90'c CHT temperature with the EGT's at around 650'c, I had to abandon the carb balance a few times to go fly the plane to warm it back up.....6 hours and 10 flights later all is well but I'm still very much in a panic.

        PS I always use super unleaded to avoid ethanol in the fuel.

        If you want to chat about it just post a reply here
        Member since 2008

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        • #5
          912/skydrive carb heat - carb ice??

          Some pics I couldn't see anything wrong, the different colours of viton (rubber) on tips on the fuel flow needle doesn't matter,but at the other end the steel is anodised different colours which refer to the different strength springs inside,these are black,the latest recommendation is a slightly softer chrome coloured steel end.

          Attached files
          Member since 2008

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          • #6
            912/skydrive carb heat - carb ice??

            Andrew, Just a thought: has the Quik got a return flow in the fuel system. I seem to remember that flexies usually haven't, whilst three-axis almost always have.

            Also, on a series system, it could simply be that by the time coolant has flowed around one heater, it's gone cold before reaching the second. If the flow isn't that fast.

            Dave

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            • #7
              912/skydrive carb heat - carb ice??

              Dave Smith wrote:
              Also, on a series system, it could simply be that by the time coolant has flowed around one heater, it's gone cold before reaching the second. If the flow isn't that fast.
              When I retrofitted carb heat to my Quantum I used the Skydrive Mk2 heaters as opposed to the Mk3 and piped as series not parallel on advice from P&M. Effectively I ended up with the same as is fitted to later P&M aircraft.

              I have checked the carb heaters for heat difference on either side by touch and there is none. I suppose I could use a thermometer, but both sides get very warm to the touch.

              It also improved the idle stability when warm compared with the situation before the fitment.

              Engine is 80 hp, obviously....

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