Ideal air/fuel ratio?

[Guest]

What's the ideal air/fuel ratio for a GS?

On my fuel injected K6 GSXR 750, I have a wideband O2 sensor along with a Power Commander V with autotune, which allows you to set a target air/fuel ratio based on RPM and throttle position. The computer then automatically adjusts the AFR to match the desired AFR in real time. On that bike, I have the AFR set to 13.1 for throttle position up to 80% up to 5K RPM and 13.0 for 80% throttle position and 5K RPM and up. The bike runs beautifully with this configuration.

I plan on adding a wideband O2 sensor with a gauge to my GS1000 to help dial in the carbs. When tuning the carbs on the GS1000, should I be aiming for 13.0-13.1 AFR like my GSXR, or some other AFR?

Target autotune AFR grid in the Power Commander V software for reference:

 

[Steve]

If I remember correctly, the stoichiometric ratio for gasoline is 14.7:1. However, you do want it a bit richer than that, which puts it into the 13-ish territory where your 750 is. Obviously, carbs are not quite that easy to 'program', but I would guess that you might be wanting something in the 12-13 range.

.

 

[Big T]

Plug chops are still needed

 

[Guest]

mmm plug chops

 

[Guest]

Plug chops are still needed

Why? Wouldn't knowing the AFR tell you what you need to know?

 

[Grimly]

Why? Wouldn't knowing the AFR tell you what you need to know?

It would be useful to know what each cylinder is doing. A lambda sensor on the collector is aggregating the output of all.

 

[Guest]

It would be useful to know what each cylinder is doing. A lambda sensor on the collector is aggregating the output of all.

That makes sense. Or install a 02 sensor bung per downpipe. Just kidding.

 

[Grimly]

. Or install a 02 sensor bung per downpipe.

Seen it done, but the owner wasn't using a multi-way AFR gauge or logger, although that would be the next step if money is no object.
Just one at a time.

 

[posplayr]

Maybe you can glean some info from here.

• 14.5-14.7 air fuel is maximum fuel mileage.
• 13.2 air fuel is maximum steady state rpm power.
  
• 12.7-12.9 is maximum acceleration power.

https://www.thegsresources.com/_forum/showthread.php?164565-AFR-Info

https://www.thegsresources.com/_forum/showthread.php?164565-AFR-Info

 

[Guest]

Maybe you can glean some info from here.

https://www.thegsresources.com/_forum/showthread.php?164565-AFR-Info[/URL]

Great information. Thank you!

 

[Chuck78]

And you might need to be even richer at idle, but you don't want to be that rich at low throttle cruising, which is also dictated by the pilot circuit. The air cooled engines run much hotter and have different requirements than water cooled engines. Leaner means hotter also. On gasoline engines at least, not diesel!
Closed throttle deceleration and closing throttle down to coast will show you much higher AFR readings, but this is fairly insignificant as the engine is not operating under a heavy load at those times.
It is the high RPM full throttle AFR readings that you need to pay attention to. Remember if you have direct linkage carbs, throttle position on your throttle grip is somewhat dependent on the RPM's that you are running. CV carbs do this calculating for you based on air velocity, with direct linkage carbs, you need to take the air velocity into account judging based on the RPMs and open the throttle appropriately on a direct linkage carb. Full throttle at 3500 RPM is not an ideal scenario, rolling on the throttle as the RPMs increase is. You can learn this just buy experience with the AFR gauge mounted, but you can also generally tell by the seat of the pants feel without the gauge.

on a CV carb, when monitoring the air fuel ratio, you don't really know exactly at what point you are at half throttle position or full throttle with the slide, since it operates on its own based on air velocity. That makes tuning CV carbs slightly trickier unless you are just holding it wide open and drag racing and just using it for the main jet, and pilot circuit low speed cruising adjustments.

I set mine for high 12's, but that was several years ago and my bike has undergone a lot of changes since then. BUT... high altitude passes did not like that so well when I was tuned for 900 feet and was cruising 4000 to 6000 feet elevation... I actually had to abort a few passing attempts on the Blue Ridge Parkway because I feared I would run out of room before the corners, as I was down 30% on power approximately.