I’m a father of 11yo karting driver and try to cover him with most support on his hobby as possible.
Now we are trying to solve the carburettor tuning mistery, we’ve been using weather station readings combined with software and eventually bought Lambda sensor to give us idea on what we’re doing.
I must say being absolute amateur newbie I got even more confused after installing it and would love to know your opinion.
I watched Power Republic videos on fine-tuning your carburettor using Lamba readings and what to aim for.
They say the sweet spot would be 0.93-0.97. Last training session, we could easily obtain that 0.94ish outcome using the usual 117-118 main jet, with a needle on p3 and something like 2,5 turns on the air screw.
I found information that for most power from your engine, you should aim for as rich as 0.88. For us, that would mean a huge main jet, like maybe even 122-123 and less air from the screw. What is your experience with this? Can you give me any advice?
One of the reasons I gave up on the Lambda for the most part was because just like every other sensor and module on the face of the planet there’s no “one size fits all” answer.
As you noted the power republic videos claim you should shoot for .93 to .97…based on their gauge / dyno. I asked my engine builder and he said closer to .90-.92 is what he sees as max power on his setup / dyno.
But that same engine builder I’ve been using for years and I know where his carbs are set and I know what my EGT targets should be and when I shoot for .90-92 on my kart with my lambda sensor the carb is richer than I expect it to be, the plugs are dark and the EGT’s are down becasue the motor is rich. I messed around with the lambda for days and found that in my application my EGT’s and carb settings and plug readings all align for me when my lambda reads at like .99 to 1.00.
Once you figure that out the lambda can help you hone in on ideal jetting more quickly than standard EGT could have, but honestly I found it to be just another value I watched and not of much value in the end. And considering we can’t run the sensor in race conditions I ditched it and went back to just EGT.
Knowing my .99-1.00 target only really comes in handy for me when the weather is REALLY cold or REALLY Hot. Those are the only two times it comes out of the box and goes onto the kart. If it’s anywhere between 60-90 degrees outside I don’t even bother it never provides me with anything I didn’t already know form EGT
That’s very kind of you to answer so comprehensively.
I will keep these values in mind and, of course, examine the outcomes and find what gives us best results.
What are your thoughts on carburettor jetting and A/F ratios in different stages of acceleration. Do you find it true that Air Screw affects only the very first 1/4 of throttle opening - idle circuit only. Then the needle 1/4 to about 3/4. So the needle position sets the amount of fuel and throttle gives air. And finally Wide Open Throttle where the main jet sets the Air to Fuel Ratio.
I assume the main jet also affects the First and Second stage, right?
But Air Screw won’t do anything when on the end of straight with throttle wide open?