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  1. #1
    GA AVIATOR
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    Rough Running 912 Engine

    My Rans S6 seems to have developed a rough running problem The engine was taken out for a Bulkhead repair and it was replaced and the carbs were balanced up, the aircraft has only been test flown for 40minutes and then flown to Swansea (40minutes) and since then it has ran rough.

    Today my friend who is keeping an eye on it at Swansea for me checked for any obvious irregularities and noticed that one Carb was tilted into a 1 o clock position whilst the other was bolt upright !!!! He straightened it upright and it started but only will run with the choke out.
    (email message as follows: )
    Hi Peter,
    Some pictures of your carbs (unfortunately my camera gave up the ghost after those 3 and I couldn't get any more).
    Now standing at the prop looking AFT,
    the right carb was tilted over to about the 1o/c posn whilst the left one was vertical. 12o/c
    That definitely does not look right and a fellow aviator and part time tinkerer thought that it looked worng to him as well. He said the float is not free to travel up and down if it is not vertical. pic 1269 shows the tilted one whilst 1270 shows the upright one. I straightened the tilted one to the vertical posn although it wasn't what I would call loose.
    Pic 1268 shows some sort of shroud under the carbs which would stop you from removing the bowls to check for water.
    Incidently as the water would be at the bottom of the tank I would think it would get drawn into the engine pretty quickly and thus after a flight should have gone through the engine and be no more? Yes ?no? .
    I could not see any means of checking for water short of pulling a hose off. Everything looked to be connected.
    I found the log books wrapped in a pink bubble wrap pouch and on checking it found where the engine had been signed off by the LAA engineer and that was about 35 hours ago. There were no remarks or engine hours added since.
    The carbs are very hard to get to not like the ones in your piccs, they are under the radiator which sits on top of the engine. Iam now very loathe to touch any more as I am way out of my comfort zone. You cannot get the lower cowling off without apparently removing the prop so this makes it even worse to get at the carbs.
    I could not in all conscience touch this aircraft without getting it certified by someone who knows what they're doing. Your engineer has even certified it quoting the relevant maintenance manual reference, which without the manual is impossible
    Sorry to be the bearer of bad news but I am most uncomfortable about this.
    Sorry I forgot to add that I took it out to run it and it started great first time but then coughed and quit and I could not keep it running without the choke out

    *pics attached*

    Any ideas ?
    Attached Images Attached Images

  2. #2
    New Member Geoff Ellis's Avatar

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    If the engine was running OK before it was removed then apart from all the usual checks on carb balance and choke cables you may have bumped one of the ignition coil triggers as the engine was being refitted. It is easy to bump them but very difficult to check / adjust on a tight engine installation and will show up as rough running and a large RPM drop when doing the mag drop check. All the infomation on setting them up is in section 74 of the heavy maintenance manual CD. DO NOT dismantle the triggers unless you have good access to the back of the engine as all the mounting washers and spacers will end up inside the magnetic rotor.

  3. #3
    GA AVIATOR
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    Thankfully it would seem to have just been muck in the fuel system.... the complete fuel system was checked today and everything cleaned through (including carbs etc) and now it seems to be running smoothly again....

    Hopefully that will be all it was.

    An interesting question...... when you are starting a 912 from cold, what do you do ? ( i.e Choke / throttle settings ) seems there are different ideas on this !!!

  4. #4
    Senior Member Polski's Avatar

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    I had an old Ford Escort that was running rough. me mate, a bit of a mechanic said, "sh1t in the carburettor" I replied "I would but I might burn me ar5e cheeks on the rocker cover !!!!!"

    G----- Tonto, get the Mogas......Hi..ho Rotax away !!!!!!

  5. #5
    Senior Member Bill Scott's Avatar

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    Quote Originally Posted by Polski View Post
    I had an old Ford Escort that was running rough. me mate, a bit of a mechanic said, "sh1t in the carburettor" I replied "I would but I might burn me ar5e cheeks on the rocker cover !!!!!"

    The old ones are the best

  6. #6
    Senior Member Bill Scott's Avatar

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    Peter,
    Before you even contemplate starting, I hope you are rotating the prop until the oil tank gurgles?

  7. #7
    GA AVIATOR
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    Quote Originally Posted by Bill Scott View Post
    Peter,
    Before you even contemplate starting, I hope you are rotating the prop until the oil tank gurgles?
    Yes....the prop gets turned over by hand until the Rotax burps

    I am only interested in the start procedure that people use on the 912 engines.

  8. #8
    Senior Member Bob T's Avatar

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    I was told that when starting from cold NEVER touch the throttle! Pull the choke on and start, it works every time for me.

  9. #9
    Senior Member micromikeuk's Avatar

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    Yes that's right Bob the way the carbs are designed if you move the throttle it will cancel out the choke completely on the Rotax 4 strokes and 2 strokes ..

    Mike

    Quote Originally Posted by Bob T View Post
    I was told that when starting from cold NEVER touch the throttle! Pull the choke on and start, it works every time for me.
    Cheers Mike

    In life those that know don't speak and those that speak don't know.


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  10. #10
    Member tracktop's Avatar

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    Quote Originally Posted by Bob T View Post
    I was told that when starting from cold NEVER touch the throttle! Pull the choke on and start, it works every time for me.
    Same here. I was taught to hand spin prop 9 turns and listen for burp with oil cap off. Then check oil level
    Adventure Before Dementia

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