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Thread: 503 performance problem

  1. #1
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    Default 503 performance problem

    Afternoon,



    Was giving my 503 Storm a first run yesterday on the beach, a bit too windy but didn't sink in the sea and I only fell out once.



    After about 30 mins of use the engine would not get up to maximum revs - sitting on 5000 max (been happily revving to 6500) - the engine was not "bogging out". So I had to call it a day.



    Anyone got a view on what to check?



    I think this is a fuel feed issue.



    I have come up with:



    1) Carburettor blockage

    2) Fuel pump failure

    3) Fuel pump heating up too much and reducing fuel pressure/creating vapour lock.



    The twin outlet Mikuni fuel pump is mounted under the carburettors on a 20mm * 40mm length of steel box. This assembly is bolted direct into the engine casing in the proper Roatx threaded holes.



    There was still loads of fuel in the tank. The spark plugs are showing a "light brown" so i think the mix is OK. Unfortunately I didn't get a chance to cool off and try again.



    Cheers,



    Keith




  2. #2
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    Default Re: 503 performance problem

    Hi



    I had this issue - are you using K&N airfilters? If they get soaked, you can get the symptoms you report. The solution for me was using foam air filters from Ken.



    Ian

  3. #3
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    Default Re: 503 performance problem

    Ian,



    Yep - they were wet



    That's probably it then



    cheers



    Keith

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