What would be interesting to me is to see a comparison of AFR and EGT. It’s been my experience that there is no relationship to one another. At peak torque, coming out of the corner, with a 2 cycle, the EGT almost always reads low, lower than it reads on the top end. Some have mistaken this for a slow response by the EGT. It’s not! With a 2 cycle, at peak torque RPM, with a pipe, you have to run very rich to prevent detonation that is caused by excessive heat and/or pressure. You can throw AFR right out the window at this point in the power curve.
Al, what does AFR stand for?
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I am considering AFR = air-fuel ratio.
I hope I am right 
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Thanks (20 chars 
)
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I’ve done lots of comparisons between AFR and EGT. There is a relationship, but it’s like comparing a butter knife to a scalpel. EGT is a blunt measurement trying to ascertain what the AFR is.You can run on two different days and match AFR readings, get identical performance, but the EGT’s will vary. AFR is a tuning tool, just like EGT, but more precise. I don’t understand what you mean by “throwing AFR out the window” at peak torque. It’s just a number; whatever that number happens to be at peak torque is what you need to aim for.
I would imagine you don’t throw it out, you adjust your target AFR to compensate. But that’s true of the entire RPM range… by that I mean that you are looking for the ideal AFR for a given RPM range.
Also keep in mind modern kart engines will generally lose power before they get to the point of detonation, especially with the watercooled models.
I’m glad you asked this. I try to avoid acronyms so as not to assume that everyone reading the forums knows what they mean.
So this is a good reminder.
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A Google research addressed me to this graph.
It was found in a aviation discussion, but I was wondering if it fits for any kind of engine.
At least in this case, there is a an-measurable link between AFR and EGT in my point of view.
Below you can find the graph and explanation for the following question:
Q.: Why does enriching the mixture ratio beyond stoichiometry give more power?
It’s because, although the Best Power mixture dumps more fuel than can be consumed by the available oxygen, the extra fuel increases the combustion speed in the charge, increasing the buildup up of pressure in the combustion chamber, and this increases the total potential energy in the air/fuel charge that can be converted to work, even though not all of fuel is burned. You could say that the excess fuel has kind of a catalytic effect, or maybe a turbocharging effect… sort of… up to a point.
Beyond a certain point, adding more excess fuel becomes counterproductive, so Best Power mixture is the sweet spot where the speed of combustion and pressures generated are maximized and the cylinder makes the most horsepower it can make (the highest possible combustion pressure) with the available displacement and airflow.
Air Fuel Ratio? I think?
Thanks. Got it now. 
Another interesting graph plotting AFR x EGT
Source: https://www.originlab.com/index.aspx?go=Solutions/CaseStudies&pid=227
“Power curve” doesn’t look like any power curve I’ve ever seen on a two-stroke! Torque or HP? What engine do you suppose this is from?
Impressive documentation,… No doubt, I love this kind of stuff.
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@alvinnunley, I edited my previous message including the source of that graph in case you want to read the text supporting the graph.
Very informative thread. It’s been from left to right and back (twice).
My conclusion is this:
- Set carb to factory specs
- Warm up kart on kart stand
- Do some pulls and try to listen for good acceleration
- Go out and adjust the Hi needle to aim for a good EGT value (1050-1150F / 565 - 625C). This on the longest straight. Match sprocket gearing
- Adjust the Low needle depending on how it handles exiting corner (Sluggish -> lean a little)
Always take notes using an air density gauge & needle settings.
Is this correct or does anyone have some feedback with this process?
Many of the racers here just use a phone app to get the proper settings based on temperature and pressure for a starting point, and then go from there.
I’ve never heard of a cell phone with a built-in weather station. Just kidding ha ha. Barometric pressure as affected by temperature equals air density. I wonder if they use the old formula or the new formula? It has been changed, around 1990 I think. I’m wondering because I see dyno charts using the old formula even today.
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Yes, using your GPS location and elevation tied into local weather conditions, it can calculate a good starting set of jets. You can then adjust from there.
Example app: https://play.google.com/store/apps/details?id=com.jetlab.honda2tjetting
Elevation tells you nothing! Local weather tells you nothing. You need actual barometric Pressure and temperature readings.
All you’re going to get from local weather services is barometric pressure corrected to sea level. What you’d like to have is the actual barometric pressure and the temperature where you’re at.
I’m curious, have you looked at weather station data recently?
Consider for a moment that there is a reason it’s used successfully and widely in and beyond karting.
Having your own weather station is ideal (assuming it’s used correctly), but there is definite proven value in using data from close by weather stations.
I started karting in 1967. I’ve been in and around it ever sense. I joined I KF in 1967 which included a subscription to Karter Newas. It wasn’t long after I got my first issue that an issue came out with an article from Bystrom instruments about using the EGT. I’ve been a fan of the EGT ever sense. Unfortunately, early EGT’s work cumbersome and problematic. If you don’t have an EGT, (now listen carefully), all that weather station stuff will do you no good, trust me. All you need is an EGT, including the information on how to use it, and an air density gauge.
I suspect you will ignore this information, but you do so at your own peril!