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912ULS Cold Starting Problem

in General Tech Discussion 12 years ago
Hi, I have a problem starting my 912 ULS from cold. On the first start of the day (summer or winter) it fires immediately but commences running with a horrible violent shaking/ grinding as if its running on just one cylinder! This continues for about 4 to 5 seconds before bursting into completely normal running which is fine thereafter. It only does it from absolute cold on the first start of the day. Once started, operation is sewing machine smooth thereafter in all stages of ground and flight operation. Any other start throughout the day is completely normal. It does seem to be a big problem as recently I found both rear exhaust down pipes to have large cracks 3/4 of the way around in exactly the same place each side. The exhaust has only done 25 hours from new as part of my new engine installation. I can only think the cracks have formed due to this extreme shaking.
I bought the engine second hand about 18 months ago. It is a 912ULS, without slipper clutch, made in 2002 with 220 hours. Although it has the small starter motor I have an excellent and fully charged battery with very short cable runs and I am confident of all the electrical connections. The carbs are well sync'd and I have the warm idle set to 1700 Rpm. My cold start technique is full choke and throttle fully closed. Its a bit difficult to trouble shoot as it only does it once a day! Any help or advice would be very much appreciated.

  • Re: 912ULS Cold Starting Problem

    by » 12 years ago

    Hi Jonathan

    Do you turn the engine over first before the first start of the day, where is the oil tank mounted in relation to the engine height, and how cold is the outside air temp where you live.

    Cheers Mark
      
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  • Re: 912ULS Cold Starting Problem

    by » 12 years ago

    Hi Mark,

    I always burp the oil tank for the level check. Then when starting I tend to spin the engine on the starter for 2-3 seconds until the oil pressure rises then flick the ignition switches on and it fires (and goes into shaking mode) straight away. (I have seperate ignition switches from the starter button). The oil tank is mounted in accordance with my Europa fire wall forward kit fitting instructions which is also in acordance with the Rotax installation manual instructions. From memory the top of the tank is very approximately at the level of the cylinders or a bit below. Temperatures I have cold started from in our wonderfully temperate UK climate is approx 5 deg C in the winter to about 15 - 20 deg C this summer!! Cheers.
      
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  • Re: 912ULS Cold Starting Problem

    by » 12 years ago

    Hi Jonathan

    This used to happen on the early Quiks without the slipper clutch fitted and using Arplast props.

    It is either a problem with your ignition modules, and as there are two completely independent systems I would rule that out.

    It is very likely that your gearbox is in need of a service, and as there is no slipper clutch fitted you would need to remove it to check if it needs shimming.

    A lot of starting and rough running problems can lead back to the gearbox, that would be my next step.

    I would also fit the larger starter motor.There is a massive difference in the speed it spins the engine over.

    I think that the engine is firing at a low RPM as the small starter can't spin it quick enough, even if you have a car battery connected to it with very short leads, ( that is why Rotax fit the large starter to the 912s), and due to play in the gearbox, it is not allowing the revs to increase enough for the advanced ignition to kick in, and so is remaining on retarded ignition, and the prop is rocking backwards and forwards between the ignition pulses.

    It will only get worse, and will cause a lot of damage to your engine.


    Cheers Mark
      
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  • Re: 912ULS Cold Starting Problem

    by » 12 years ago

    Hi Jonathan,

    I'm with Mark. Toss the old starter and get the newer style high torque starter. It actually turns the same speed, but has more torque to get it to rpm and keep it there where the rpm's should be for starting. Your gearbox may need to be looked at as Mark stated. I would not recommend the running it 2-3 seconds and then flipping the ignition switches. Turn it all on and fire it up. When you do it your way you are pumping fuel in without any plugs firing. The fuel pump is still putting fuel to the system and you are flooding it which would cause all the shaking in the beginning.

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

      
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  • Re: 912ULS Cold Starting Problem

    by » 12 years ago

    I'm with Roger. You probably have one carb flooded and it takes a few seconds for it to clear up. During that time you are only running one one side of the engine.

    Alan
      
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