Mark B. wrote:
Do you have any information on how to jet a carb using exhaust temperature?  I've been told by racers this is the surest way to get it right, and quickly.  I don't know where to find what the "correct" temperature is, though.  Any help is appreciated...

Mark Bxxxx
Test Engineer


Errr..... from what you wrote - "they" (the "racers") may have missed what makes what you wrote, "more correct".

The reason why you can't find "correct" numbers is that the "correct" number wanders up and down in about a 200f range (in current engines). My airplane runs best somewhere between 1300f and 1450f, for example - and that depend on barometric pressure, load and ambient temp..... My old 2 stroke racebike liked 1300f at full throttle. I tuned a Kawasaki ZX9 and it wanted, depending on the cylinder, 1275f to 1375f when it was jetted correctly.........

Really - You know how, over the years, you found that the "school" taught stuff doesn't work at 100% and you have to "tweak" processes to work in the real world? (please say "yes" :-)

In theory, lot's of school taught stuff works - but - more constant factors become variables when you and I actually use them...... like o2 level in the exhaust..... lot's of things affect that level (including mixture). Same with egt - if you go up in dynamic compression, you cht goes up and your egt goes down. Drop dynamic compressions and the inverse occurs.
Now, both of the above egt values are as referenced to values obtained when the engine is jetted to make best power (now, really, that IS  what you were looking for, yes?)

So - yes, I do have information on how to jet a carb by egt, but it's part of some writing describing how it's incorrect....... Is that what you'd like?

Smiling while I'm writing -

(getting an idea why they call me the Evil Curmudgeon?)