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  • #46
    Exhaust Gas Temps

    I'm based at Chilbolton near Andover, Hampshire. Where are you?

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    • #47
      Exhaust Gas Temps

      I'm up at Stevenage. You aren't too far. If you aren't in a hurry bring it to the Popham Microlight event and I can meet you there perhaps?

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      • #48
        Exhaust Gas Temps

        Dominic - can you PM me your telephone number so that we can liaise?

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        • #49
          Exhaust Gas Temps

          It's a very long shot but how dirty are the air filters?

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          • #50
            Exhaust Gas Temps

            I'll be checking just that within the next few weeks......I was under the impression that they'd been done shortly before I bought the aircraft but there's no harm in doing them again!

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            • #51
              Exhaust Gas Temps

              Phil I had a brain storm in the workshop today.....how about trying a Colourtune plug? This would show exactly what is going on inside.

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              • #52
                Exhaust Gas Temps

                Phil,

                On the 17th you posted that you've got iridium plugs in your engine, but that you have to keep checking the tightness of the screw tops. You can get solid top iridiums for our engines. I've got them in both of my 462's. If I remember rightly I bought them from sparkplugs.co.uk. I also gapped them to .6mm as I think the gap they come with is a bit big for the points ignition on my engines. They still work very well though, and make starting a breeze.

                Best regards,
                XL's forever! Well, one of them anyway. It's all I can afford, not to mention the Raven and the Mini-Max. Oh, and I almost forgot the Spectrum as well :-)

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                • #53
                  Exhaust Gas Temps

                  Thanks Bob....Sparkplugs UK tell me that the BR8ES Iridium equivalent is BR8IEX Solid Top.

                  Well spotted!

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                  • #54
                    Exhaust Gas Temps

                    Well....... The latest in the saga is that I've changed the main jets in the carbs to 162 size (from 165), expecting the EGTs to be a fair bit higher but......

                    No difference. They're still both below 500 so I must draw the conclusion that the gauges are faulty. It looks like the needles rise to 480 or so then no higher. Bother! (other expletives deleted).

                    What good are gauges if they tell porky pies I ask myself!

                    Hopefully the external instrument I've ordered from Ebay (see earlier in this post) will arrive from China soon and I'll check the accuracy of my Shadow's gauges and report back.....unless anyone's got a spare EGT gauge I could borrow in the meantime for a day?

                    I also intend to order a Colourtune plug!

                    Phil.

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                    • #55
                      Exhaust Gas Temps

                      Phil, have a look at this article, it might be useful: http://rst-engr.com/rst/articles/egtcht.pdf

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                      • #56
                        Exhaust Gas Temps

                        Just a thought where are the 'EGT probes situated - are they the correct distance from the cylinder wall?

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                        • #57
                          Exhaust Gas Temps

                          Well I got one of these with an EGT probe.

                          http://www.ebay.co.uk/itm/Black-Type-K-Digital-Thermometer-TM-902C-Thermocouple-Probe-50-to-1300-/281901918185?hash=item41a2a9e7e9:g:qFUAAOSwX~dWjB9 u

                          To see how it compares with the Westach anolog instrument I did a side by side test...I have a probe in each branch of my 503 manifold giving me a reading from both cylinders...I removed one and replaced it with the new ebay one.

                          At first the digi was giving an exactly the same reading as the analog gauge at 300c which was at around 2500rpm...on increasing the revs so my Westech was reading 500c the other digi type was still reading 300c.

                          So not sure why that should be...the digi meter is running from a probe that does not sit as deep into the exhaust branch but they are both 400mm out from the pistion

                          Any ideas wally.
                          "When once you have tasted flight...you will forever walk with your eyes turned skywards..."

                          https://www.youtube.com/user/nickjaxe/videos.

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                          • #58
                            Exhaust Gas Temps

                            A 165 jet and 162 thats only 3cc of petrol different...now I can never remember is that per minute or per hour....maybe you need a bigger step to see a difference.

                            Question for you guys....if using a color-tune...what would we be looking for...is there a benchmark color.

                            Nick.
                            "When once you have tasted flight...you will forever walk with your eyes turned skywards..."

                            https://www.youtube.com/user/nickjaxe/videos.

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                            • #59
                              Exhaust Gas Temps

                              Hi,
                              My thoughts on this and understanding are that the Rotax is set up for worse case and so is jetted for sea level. The result is that even out of the box it tends to run rich.
                              As the carbs get some hours on this tends to get worse due to wear.
                              Our cheap EGT instruments are a very good way of keeping an eye on things but unless you are comparing results with other engines are in my opinion best viewed on as an indication of change rather than an absolute value.
                              It is useful to realise the results from the main jet and needle/needle jet are completely separate and operate at different stages of flight so if you want to effect a change I think you need to take into account these things as well to get the results you want.
                              Changing the main jet for a smaller one will only effect the fuel burn on take off and climb out so if you are into cross country flying will only make a small difference where as the needle gives you the mixture in cruise so will make a difference.
                              My personal choice is to stay with a slightly rich main jet and optimise the needle for the mixture.
                              If the EGT readings get a bit high you can then either back off the power or give it full throttle both which will reduce the readings.
                              This system if used sensibly gives you a safe way of setting the mixture with the benefit of less fuel, more power and a smother engine.
                              Most concentrate on getting the main jet correct which if you were doing a bike would be the correct way but air-bikes are used slightly different.
                              Mick Broom
                              Member 909
                              Shadow G-MWTN

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                              • #60
                                Exhaust Gas Temps

                                Although in principle all "K type" thermocouples should give exactly the same output per degree, I assume that you are not using the "bead" type thermocouple which is standard with that meter?

                                Rather strange that the meter only reaches 300C.
                                I guess if the probe is not inserted as far5 into the tube, then it will tend to under read at higher revs as it could possibly be in the "cooler relatively static" outer layer of gas.

                                One rather "drastic" way of bench checking that thermocouples/meters combinations are giving roughly the correct "high end" reading, is to "tightly wrap" the thermocouple in "thin" 6063 T6 or 6061 T6 aluminium and heat with gas blow torch (MAPP gas") until it melts
                                6063 T6 melts between 615C and 654C
                                or 6061 T6 between 582C and 652C

                                Hope it helps

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