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  1. #1
    hnesitd1's Avatar
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    Fuel Tank Placement

    Gentlemen: Recently I had an interesting problem with several glow engines. The symptom was that the engines would start and idle well but the minute the throttle was opened the motor would die. After looking for air leaks, etc. I think I've discovered the problem. Tthe gas tank, although located properly with-respect-to the spray bar, was improperly positioned. As I understand it, the spray bar should be 1/2 the distance up the gas tank height as seen from the side, ie, this is the positioning for the tank. However, with this configuration the engine is supplied with a gravity feed fuel supply; as we say in the NAVY, the tank beomes a, "HEAD", tank. With this configuration, opening the throttle provides a super rich mixture cooling the glow and stalling the engine. Lowering the tank so the engine must demand fuel (seemed to) cure the problem. Incidently, the low speed idle was set correctly. Has anyone experienced this? I suppose the now the engine would run rich inverted, eh? What is the correct answer with-respect-to gas tank height? Comments??
    What has four legs and an arm? A happy pit bull -Doc Hemp (2006)

  2. #2

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    Fuel Tank Placement

    hnesitd1:

    Dude, I went out and bought a cheap ARF yesterday to fly today. You know buy it Satruday, build it............ So the story goes...This arf is set up to install the engine upsidedown. I'm going with t two stroke .46 and have never tryed the upsidedown thing. so sitting here waiting for epoxt to dry I'm reading post to kill time and now I'm scared to install the engine and fuel tank LOL...
    I have read of others moving the tank from factory suggested location so I plan to do this as well.
    Buttttt,,,, What about the inverted rich condition you speculate??
    Please think out loud further. Seems to me that not having a float bowl these type carbs should be adjustable to run in most any position provided air and fuel are supplied properly.

    Miloh.
    \"My life has a superb cast but I can\'t figure out the plot.\"

  3. #3
    RaceCity's Avatar
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    Fuel Tank Placement

    Here comes 350 posts regarding pumps, regulators, etc,etc,etc.

    The tank position is typically specified by the mfr of the engine. It is common to have the tank Centerline (viewed from the side) to be on a level with the needle valve of the engine with the model in a level attitude. There is usually a +/- 1/4" or so latitude in the positioning before hassles begin to set in.

    I am assuming you are using muffler pressure...it helps make things just a touch less critical.

    The optimum location will be determined through flight testing. A skootch higher...a tad lower....you get the point.

    There is always a bit of a compromise with an un-pumped, un-regulated fuel supply, but the basic suction feed system has worked for years in millions of models...it will surely work in yours.

    Just do your best to keep fuel lines short...avoid unneccessary in-line gadgets and you'll get good results.

    Regards,

    'Race
    AMA 63990

  4. #4

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    Fuel Tank Placement

    Ok: RaceCity

    Chime right in there!! this is as I though but had never ask any body. Thanks for your help.
    I am using muffler pressure and I never have used any kind of gadgets so I think I'll ok here, just never tried a 2 stroker upsidedown.

    Miloh.
    \"My life has a superb cast but I can\'t figure out the plot.\"

  5. #5
    RaceCity's Avatar
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    Fuel Tank Placement

    Miloh...

    The only real quibble IMO with an inverted engine nstallation is that they tend to be easy to flood. Be careful if you're using an electric starter!!!!

    Further, you may find that needle settings (ie: idle) tend to be a bit more critical than a side or upright mounted arrangement. Other than that...it's fine.

    Enjoy!
    AMA 63990

  6. #6
    hnesitd1's Avatar
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    Fuel Tank Placement

    With the tank mounted correctly and by disconnecting the fuel line from the carb, fuel would pour out of the fuel line (of course). However you can see the problem if the the throttle is opened wide from idle, ie, super rich immediately and the glow plug gets cooled off - engine dies. The engines were ASP .46s. Raising the tank to ensure a demand supply seemed to cure the problem however the mounting is contrary to standard mounting protocols. It seems to me the engines have a manufacturing defect in the carbs, eh?
    What has four legs and an arm? A happy pit bull -Doc Hemp (2006)

  7. #7

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    Fuel Tank Placement

    hnesitd1:

    I just got mine together and out in the yard, this is how it went, the motor is a tower pro .46 bb. very powerful and reliable motor for me so far.
    The tank in the kit is very small so I opted for a larger one and set it in the best I could, not level but pretty close and it is higher than the carb. no other option with the motor inverted.
    I did use a electric starter and it did not flood but started right up and ran pretty good but did fatten up and die. so in with the low end screw and now it idles very nice.
    Did not get a chance to fly it but in running it up it seems to take throttle good and just needs a little fine tuning at the field. maybe a different prop.
    Might get to fly it tomorrow evening.

    Might as well show it off.

    Miloh.
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    \"My life has a superb cast but I can\'t figure out the plot.\"

  8. #8

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    Fuel Tank Placement

    One more.
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    \"My life has a superb cast but I can\'t figure out the plot.\"

  9. #9
    hnesitd1's Avatar
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    Fuel Tank Placement

    Yo! Miloh - nice looking airplane. The problems that I experienced were very strange and I figured that I'd toss out the symptoms with what I considered the cause and cure - hopefully saving some bro max frustration. I was convinced that I had an air leak somewhere. Have a nice day.
    What has four legs and an arm? A happy pit bull -Doc Hemp (2006)


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