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DC conversion

in 2 Stroke Technical Questions 6 years ago
I've converted my 503 to dual carbs, set up per manual. Installed an electric fuel pump in line (series) to the pulse pump. (My fuel head is only a few inches) With lots of priming the engine starts and runs fine at 3000 or more, but when I bring it to idle, 2000 rpm, it runs smoothly for a while (30-90 seconds) then begins to slow down and finally die. It does this with the electric fuel pump running or off. Once it starts to die, opening the throttle doesn't have any effect.
What am I doing wrong? Any suggestions?
Installation manual recommends pumps be parallel, but I think that would be too much fuel pressure.

  • Re: DC conversion

    by » 6 years ago

    When it stops look at the fuel level in the carbs bowls see if the level is low or high and both the same.

    Nick.
    Thank you said by: Bill Hertzel
      
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  • Re: DC conversion

    by » 6 years ago

    You have a problem that is not a Series/Parallel issue.
    Before the start, enough fuel dribbles in by gravity to fill the carb floats.
    It may be that once started there is not enough fuel being delivered to keep the carbs full and after a minute or two, the carbs run out of fuel.

    The first thing to confirm is that the Fuel Filter(s) is/are not blocked.
    Pull a hose off of one of the Carbs.
    Turn ON the Electric fuel pump.
    The pump should deliver a Quart to Half a Gallon of fuel into a gas container in a minute. Time it.
    If it just a trickle, start opening the fuel lines to find the restriction.
    It will typically be the fuel filters, the input connectors of the fuel pumps, or the upstream side of any other fuel fittings.

    Bill Hertzel
    Rotax 912is
    North Ridgeville, OH, USA
    Clicking the "Thank You" is Always Appreciated by Everyone.

    Thank you said by: Conrad Nordquist
      
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  • Re: DC conversion

    by » 6 years ago

    When it stops, look at the fuel level in the carbs bowls see if the level is low or high and both the same...


    Also a good idea!
    I might add that you will want to turn off the fuel shutoff valve Immediately after the engine quits or a slow flow of fuel may refill the floats before you can get them off and mask the problem.

    Bill Hertzel
    Rotax 912is
    North Ridgeville, OH, USA
    Clicking the "Thank You" is Always Appreciated by Everyone.

    Thank you said by: Conrad Nordquist
      
    Report

  • Re: DC conversion

    by » 6 years ago

    Still having trouble with my nearly new 503 DCDI. It will run ok at 3K to 5K, but refuses to idle. I've varied the idle air screws from 1/4 out to 1 turn out with no difference. I've blown out the idle jets and all holes look clear. Fuel flow is good, 30 gph at the pulse pump from the electric pump. It won't start without priming, even when warm. All plugs show a spark, but cyl.#2 runs much cooler than #1. Air temps are around 70 degrees F., altitude 800' so it's close to standard day. I have catalog recommended jets, needle, etc.
    I think I may have an ignition problem, weak spark on Cyl #2, as well as a carburetor problem.
    I've addressed all the recommendations you've previously given and still no luck. I'd welcome suggestions, ideas, or contacts who can look at the engine in Southern California.
      
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  • Re: DC conversion

    by » 6 years ago

    When you say wont start without priming...what do you mean by priming...

    Weak spark...is that observer the plug while you crank...and is it both plugs they you say have a weak spark.

    Nick in the UK.
      
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