True dat, if you buy a KTM you'll be buying a 'dongle' or hacking resistors into the circuits to trick the EFI to give the engine a proper mix... pretty common to see various hacks for the big manufacturers. I purchased a Beta due to their low volumes they have a lower standard to meet for emissions.. the EFI on my Beta is spot on from sea level to 13,000' elevation.

14.7 is ideal, so if it indeed was running at that number, then it would NOT be running lean, and I would not have to put on choke when trying to accelerate above 40 MPH.

The increase to a 110 main jet from 88 did the trick!

Eh, 14.7:1 is ideal for fuel consumption and emissions, but 12.7:1 is the peak for power. I wouldn't think it would need a choke to go faster, but it's not impossible/improbable.

Actually, 14.7:1 is the ideal compromise for fuel consumption and power, well above that is ideal for emissions, and well under that produces black smoke but more power. No doubt the bike out of the box was set for well above 14.7, but now is hopefully around that number.

You misunderstand, and you're somewhat incorrect. 14.7:1 (1 λ) is the best balance between burning everything and is okay for power on gasoline. Since everything is burning in the 'cleanest' possible way, that is the ideal balance for pure gas. Ideal stoich, 1 λ, for E85 is 9.8:1. For most fuels, the best for power is .86-.9 λ. Not sure what it would be for E5-10, but it would be a bit richer than what is best for power with gasoline at 12.6:1. Most FI systems are designed to go richer at WOT, as it provides more power, my guess in part because it keeps the charge, and thus the engine, cooler.

Engines running leaner tend to detonate more easily under load, and also produce more NxO, which the EPA strictly regulates now. There have been designs that run okay while running leaner than 1 λ for great fuel economy, like the Honda CVCC designs of the 70s-80s, the CRX being a good example of that.

For more reading: https://help.summitracing.com/app/an...2Ffuel-mixture

You are correct. I've done quit a bit of tuning on EFI turbo and supercharged engines. Drag race for many years.14.7:1 would grenade an engine quick. I always shot between 12.6:1 and 13.0:1.

Also, it's a bit strange to go from asking, "what does sputtering mean" to lecturing about proper afr.

Great useful info here from JerryHawk250 and franque. Thank you both. Would you mind indulging me for learning purposes? What I have learned in the past was that stoichiometric ratio is good for idle and cruising, but rising to about 12.7 is ideal during acceleration. Would you say this is correct?

Give or take, but look at the article I posted. Engines in a higher state of tune are more sensitive (both to detonation and engine failure), but something lower performance like these bikes would probably not be in danger of detonation even if it didn't enrichen much if at all at WOT, it would just cost it some HP and acceleration. That's why rejetting them gives a significant improvement in power.

Thank you, sir. Missed the article you posted. I will go check it out.