Wrong silent cap combo, over fueled?

Discussion in 'Fettling Forum' started by hikerduane, Jan 26, 2020.

  1. hikerduane

    hikerduane Subscriber

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    I have had this old 1.75 L Monitor for maybe six years, I tried a smaller jet a couple years ago and the flame was low so put the old one back in. At one time, it ran like it should, but I think I removed the caps and put them on a more desirable stove, thought what I then put on this stove worked ok. Outer cap use to get reddish. What is going on now? Notice the nine hole inner cap sits below the tube/venturi. I swapped parts around yesterday, only difference I noticed was if the outer cap was lifted a little, the flame on half the outer cap exited the holes as designed and were blue. Telling me over fueled or oxygen starved. Notice the flame around the burner skirt holes. What is the proper cap combo for this beater?
    Also, gets worse with more pressure.
    Duane
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  2. igh371

    igh371 SotM Winner Subscriber

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    As I understand it the 9 hole inner cap was designed for certain Optimus models which also had holes in the central riser spigot too (supposed to reduce danger of underburn). Might be worth trying substituting an inner of the correct height which is without the additional holes.
    If that doesn't sort things out, keep the plain inner in place and try a selection of different outer caps - sometimes one will be found that works well where others don't. In situations like that it is never easy to see any obvious reasons for which do or do not work the best, but it does happen!
    Good luck,
    Ian:thumbup:
     
    Last edited: Jan 26, 2020
  3. presscall

    presscall United Kingdom SotM Winner SotY Winner Subscriber

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    @hikerduane
    I suspect the jet rather than the caps, a partially blocked jet or (less likely) leaking at the burner threads - though I’d expect that to be obvious when leaking fuel vapour ignites in the vicinity of the jet.
     
  4. hikerduane

    hikerduane Subscriber

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    Of all things that was a easy fix. After exchanging numerous caps, the cap combo off my Valor worked best, but on a impulse, pricked the jet. Presto! Instant results. Put the caps shown back on and like my old notes on the tag say for the stove, likes lots of pressure. Also thinking though that a outer cap a tiny bit higher would work best like my Valor cap is.
    Thinking with a lower pressure stream of vapor, the vapor wasn't able to get pushed out the intended holes in the outer cap, instead burning around the holes in the skirt.
    Thank you.
    Duane
     
  5. hikerduane

    hikerduane Subscriber

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    Thanks John, got it.
    Duane
     
  6. hikerduane

    hikerduane Subscriber

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    @presscall, so what is happening then? With the partially blocked jet, why at higher pressure does the flame go yellow?
    Duane
     
  7. presscall

    presscall United Kingdom SotM Winner SotY Winner Subscriber

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    @hikerduane
    Disrupted fuel/air mixing, Duane. Vapourised fuel efflux all over the place and not the fine stream headed centrally up the burner tube where the fuel/air mixing begins.

    Increasing tank pressure accentuates the yellow flame because more fuel reaches the interior space of the burner caps but because it didn’t arrive there as a high-pressure regular laminar-flow stream but as much lower pressure vapour, poorly mixed with air, it burns yellow (fuel rich).

    John
     
    Last edited: Jan 26, 2020
  8. Tony Press

    Tony Press Australia Subscriber

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    That’s a much more sophisticated answer than me saying “a partially blocked jet will shoot fuel all over the place and some of it won’t get enough air to ignite fully”. ;)

    Cheers

    Tony
     
  9. presscall

    presscall United Kingdom SotM Winner SotY Winner Subscriber

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    @Tony Press
    Sophisticated? Sophisticated? I’ve been to Leeds!

     
  10. hikerduane

    hikerduane Subscriber

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    Thank you guys, I guess I was partially right, just unable to explain it after I pricked the jet.
    Guess this is what I get when I try to let the preheat pressurize the fount some instead of waiting for the alcohol to completely burn offer allowing a slight candle flame.
    Duane
     
  11. Ed Winskill

    Ed Winskill United States Subscriber

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    John started it....

     
  12. MrAlexxx

    MrAlexxx Subscriber

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    I have been known to say to a few on here that if John doesn't know then we are in real trouble. lol

    Alex :)
     
  13. hikerduane

    hikerduane Subscriber

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    Things have to sorted out sometimes, a issue could be caused by one of a number of things.
    Duane
     
  14. Lennart F Sweden

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    As you have a tall center pipe you should make sure the outer cap has enough space to let the gas mixture pass freely out of the center pipe - been there!
     
  15. hikerduane

    hikerduane Subscriber

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    I'm now wondering if I need to prick my UFO Radius stove as it burns yellow, at one time burned correct. Even tried a different cap.
    Duane