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Summer starting problems again

in 912 / 914 Technical Questions 13 years ago
It happens like clockwork. If I leave the plane for more than a week in hot weather, battery charged or not, it won't start. It's not flooded. Every single time it does this, I can come back the next day and it will start and run absolutely fine. Yesterday I had to use full choke and full throttle to get it to turn over.

The only theory that makes sense is that fuel is evaporating all the way to the intake of the fuel pump. Cranking it seems to start a trickle of fuel, which the following day seems to be enough to get the pump working. I'm sure an electric boost pump will fix this.

This is very frustrating, as I have to spend time cranking the engine the day before I need to use it. Multiple flights in one day, and hot starts are not a problem.

Happens with mogas and 100LL mixture. I don't run 100% 100LL (it's almost $8/gal at my home airport)

  • Re: Summer starting problems again

    by » 13 years ago

    Howdy Scott,

    Is this the Scott from TX? High wing CT?
    Are you shutting off the fuel valve after your last flight of the day? You should. Are your plug gaps at .023 - .027? Are your carbs synced and the idle set to 1700-1800 rpm? If the idle is set too high or too low as it can affect your starts. Is your first start of the day with full choke and no throttle (or at least no more than 10% if you have a low idle)? It could be air in the lines, but doubtful. When I do a hose change and drain the entire fuel system. I just put fuel back in the tanks and crank the engine (on a high wing). It usually starts within a couple of seconds. If it is a low wing with an auxiliary pump I will turn it on momentarily. I rarely start engines with both pumps and usually don't have any issues. The mechanical pump usually does a good job.
    You need to put a mechanical gauge on the fuel pump and just double check the pressure. After you try a few starts, pull the plugs and see if they are wet or dry.
    This is a good start to figure this out, but there could be more to talk about after you try this and answer those questions.

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

      
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  • Re: Summer starting problems again

    by » 13 years ago

    Yes, it's the CT. Carbs synced after the hose replacement last fall, idles at 1800.

    I tried the fuel valve last summer and it had no effect. Could the gascolator be slowly leaking, siphoning fuel from the carbs? Whenever I check the gascolator, fuel comes out easily. I usually drain an inch into the fuel sampler. Maybe I should drain a pint or something.
      
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  • Re: Summer starting problems again

    by » 13 years ago

    Hi Scott,

    Has this hard starting always been the case or only after a specific maint. procedure?
    The CT will kick right over even without the fuel pump. I have tried it without the fuel pump even in the system and I have tried it with the fuel pump in line, but not on the gear box. With the fuel pump completely out of the system and just the hoses spliced together on the CT it will run full throttle and never miss a beat. With the fuel pump in line, but not functioning it will make 4800-5000 rpm without missing a beat, but after that it will sputter. I'm a little more suspicious about the fuel pump or the carbs themselves. It would only take one bad carb to make it hard to start. I would also check the carb chokes to make sure they open and close all the way and if they have ever been dismantled if the chokes went back in the correct way. Checking the float levels and how they float in the fuel. Use a set of gauges and sync the carbs and see if there is any signs of a problem. Put a mechanical gauge on the fuel pump line and see if it matches what is on the Dynon if you have a Dynon. You need to do a little more diagnostics to get to the bottom of this.

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

      
    Report

  • Re: Summer starting problems again

    by » 13 years ago

    It has been running fine since last fall. Only when it started to get warm did this problem appear. After the hose replacement, cold starts were easy all winter.

    I'm trying something else. When I shut down the engine, I immediately take the cowling off. The gearbox is quite warm, and perhaps the heat soaking back to the fuel pump is boiling off the fuel and starting this process that replaces fuel in the pump with air.

    When the engine is running, all the pressures are normal. The Dynon matches actual fuel consumption to a few percent.

    Is the gascolator a possible cause?
      
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  • Re: Summer starting problems again

    by » 13 years ago

    Looks like it was never a fuel issue. I replaced the ignition modules with the new soft-start ones, and she started instantly after sitting for 3 weeks.

    If you have older (~2006) ignition modules and you get some strange starting issues, you might want to check this. The mantra used to be "the 912 ignition has never failed". I don't think the ignition has failed in cruise flight, but there can be issues at low RPM at both high and low temperature extremes.

    This had been driving me crazy for 2 and a half years. Now it appears solved.
      
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