O2 Sensors, AFR's, Factory Pro...More info, more questions

[81xsproject]

So, things have worked out with the MSD (another story) enough to get to test out my AEM wideband O2 system. The AFR's I got on my first test ride were both good and bad. From what I can tell, through the low and mid range (<5k) with a load, the bike is rich with AFR's run from around 11-13. At WOT, the bike leans out as the RPM rise and at about 7k, the AFR gets right around 14.

Currently, I am running 117.5's with 45 pilots, 4-1, and pods. This, I believe, is in accordance with the jetting guide.

Why is it, that on the Factory Pro tuning page, they do not even mention the pilots in the whole tuning process? Not to mention, they recommend adjusting the float height as a way to tune the LOWER rpm...? What the heck?

What is the optimal performance AFR?

Should I go back to my stock pilot, or drop the float level?

[AlanB]

Hi 81XS,

Most performance tuning is aimed at better PEAK power, so pilots, vac advance, fuel economy, etc are all irrelevant........ Until you try to drive it!

When I was involved with the Dyno shop, we got loads of guys in wanting their CBRRR/R1/GSXR to be "FASTER.... and don't worry about the lower range; I never drive there"

They would happily sacrifice 30 BHP in the midrange to gain a couple at peak, so they could brag to their buddies, and show 'em the sheets.

Many were back in a week to tell us that we had messed up, 'cos the bike was unrideable. The brighter ones just had us take the stage seven Jet kit out again...... and give 'em back the midrange.

Most people do not ride their bikes nearly as hard as they think!!

AlanB

[TopCatGr58]

Hey Jessie,

From what I've read, 14 is the optimal AFR, but you didn't mention WHERE you had your pilot jet screws set??

IF you have them 1&1/2 turns out or more, you might just try turning them in a 1/2 turn and retest! IF too rich, turn them in again! The Pilot jet does affect the midrange/and transition to mains, but at a diminishing amount as the mains kick in, so you should be able to keep your ~14 AFR mains result without having to change your float level!

I'm running 4-1, Pods, BBK, adn 117.5 mains, but only 42.5 pilots only because years ago I bunged up a couple trying to get them out....way before I learned all the tricks on here, and so I just turned my pilot screws out a bit more, and it seems to respond just fine! YMMV, but the easiest would be just the try to tweak the pilot screws first! IMHO!
T.C.

[Guy_b_g]

14.7:1 (stoichiometric) is a theoretical perfect burn with no fuel or air left - but you need additional fuel to avoid detonation.

12.5:1 is generally considered optimal (power) for a naturally aspirated motor.

Between 12.5:1 and 14:1 are the best settings for economy.

A lot depends on the engine's state of tune. None of these numbers but the 14.7:1 is a hard & fast number..and if you tried to run at that setting the bike would run like poop and may even cause detonation damage or melt a piston.

Of course this is also steady-state, the mixture should be richer under acceleration or load, hence the need on some engines for accelerator pumps, whereas our CV carbs have ... CV! and the fuel curves are built in to the metering system including the design and taper of the needle.

[Guy_b_g]

"14.7:1 (stoichiometric) is a theoretical perfect burn with no fuel or air left - but you need additional fuel to avoid detonation".

umm...I meant no fuel or oxygen (not air).... There'll still be other gasses left because air is only about 20% oxygen...and even at 14.7:1 there is still enough oxygen left to measure...some air/fuel meters measure the residual oxygen...some measure CO2.