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...No one I know has achieved much better than 100 deg C spread on EGT, which is way from acceptable...

I'm away from home, with only this single pic to help me relate to this discussion. Can anyone interpret it for me?

 

This is my reading at cruise; it looks okey, but without a side scale it's hard to read the temp spread between cylinders. I presume the big numbers are the the hottest cylinder. On the CHT side the bars only appear when 100C is reached, so I guess there's 50C between the bottom and the dotted line, which is the 150C CHT I've set to trigger the alarm. Is that what the small 150 means?

 

I can't recall at what temp the EGT bars appear, so how do you read the spread?

 

What does the little 850 on the EGT side mean? Is it the dotted line across all 4sensors and does it trigger the alarm?

 

 

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Alarm settings?

 

If you had egt at 850 it wouldnt be for long, expensive bits damaged

 

Many ems setups pick out peak cylinder temps as with mix control that is the one you lean for

 

In Jabiru this peak cylinder can swap positions with throttle settngs and load

 

 

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The answer is,bearing in mind that the bing loves straight air into it

 

The engine rear is not in the centre of the firewall so using the crankcase join line I moved the whole airbox over so that it was aligned with that ,so the air has a straight run to the carby

 

I made a new cobra head carby intake with a cross in it to further keep the air straight

 

As suggested by Don from Jabiru I removed the airfoil type shape from the original plenum chamber that I have and replaced it with a 12mm dowel because the dowel appears to stir the mixture more.maybe a 15mm dowel that was knurled would do an even better job but I am too lazy to try as my egt’s are close enough for me

 

Further to that I level the carby with The plenum using two rulers to get the rulers parallel with one on the plenum and one on the carby

 

Jetr is right that the egts change with throttle settings and the speed of the mixture coming in,at full throttle my number 5 mixture is the hottest instead of 2 .at full noise there is a little spread but nowhere near 100 degrees c.will be away for a week or so will get a full throttle reading when I return

 

Every bit has helped I think but I got the gauge last so don’t really know

 

I may have uttered a few incantations as well but can’t remember

 

 

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EFI is in the auto world for Environmental reasons. DIRECT injection is the next step. There's no way carburetters would meet requirements of today and I'm not advocating carburetters (especially the Bing CV) as good... The enrichening of the carb at high power is required regardless of the egt spread you get. When Jabiru engines went lean the problems got much worse. Lowering the compression and retarding the engine don't increase efficiency and only reduce the probablility of a problem happening without preventing it. High altitude operation achieves the same thing. so there's a message there. Nev

 

 

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Great that this worked on yours Rodknee, Ive done all the same and then some, and had some improvement but still have up to 100 difference. Sometimes less but not reliable over throttle settings.

 

Ive implemented every mod Jabiru can come up with, and just when you think its pretty good it seems to change again.

 

Lean running is a big problem for sure so extra fuel is cheap to cool things down.

 

Wondering if air velocity through carb is too high?

 

 

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That will only happen at WOT on the ground IF the carby is too small for the engine or if the dashpot spring is too strong. Both of these issues would reduce the engines output. A fixed venturi that is too small will get progressively richer at the top end unless there are some design feature(s) in the carb that will counteract the tendency like air holes in the spray nozzle that emulsify the fuel stream at higher suction/ velocity situations.. Nev

 

 

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