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AFR effect on exhaust note

Understanding AFR

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Hi everybody,

My name is Manuel, i'm from Argentina and i'm currently applying the knowledge i've incorporated thanks to the tunning course on my 2017 Yamaha MT07.

The bike is set up with the original air filter (it has a snorkel-type of choke to breathe through) and with a Akrapovic titanium exhaust.

With the original tune and the new exhaust, the AFR was a disaster, hitting up to 16.2 on some points.

Now, i've managed to get the AFR right where i wanted it to be. But here is the interesting thing:

The exhaust has a 2.75-3 inches of diameter on the exit. With the bike running lean on the beginning, the sound pressure level generated by the exhaust was way bigger than after the tune. I've noticied this because after the last tune (and definitely the most accurate one), on the test run i though i left something like a rag on the exhaust, since i could notice the decibels generated were less than before.

For ex:

at 5% TPS @ 3000rpm, i'm running 14.1 AFR, as where on the original tune after the exhaust install i was running somewere on the 14.9-15.2, and on this range of rpms, when cruising, i could notice a big difference in sound.

Any one has an idea on why this phenomenon happens?

Thanks everyone, and sorry for my rusty english!

What exactly is the tune changing? Do you have before and after logs?

hotter exhaust?

Hi both Arghx7 and Superman07!

Thanks for the reply! Arghx7, when i mean by tune changing is basically is the level of Decibels and the fundamental note of the exhaust, both seem lower. And Superman07, i can't really measure with the tools i have in hand the exhaust temperature, but my guess is that the ex.temp must be lower than when it whas leaner, since the combustion chamber temp must have dropped with the extra fuel! I'm gonna try to obtain the logs from the laptop so i can show you guys!

Again, thanks!

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