Significance of Throttle Position to Engine Performance

[Evo160K]

Recently I used my homemade dual a/f meters and O2 sensors to set the a/f mixture on my evolution engine.  It's not fuel injected.  I made these settings during a sustained run at 3,000 rpm on a flat road.  On a road with a sustained climb, at 3,000 rpm my meters showed the engine running leaner than on the flat road.  I'm trying to understand the significance of the throttle position to the mixture.  On efi bikes, what adjustment does the ecm make for throttle position, add fuel, reduce fuel, or what?  Thanks for your input. 

[PC_Hater]

Under normal circumstances the simple answer is that an EFI bike does exactly what a CV carb does - adds fuel related to throttle position and rpm.
When aftermarket cams and exhaust systems are fitted the factory settings for the EFI need changing. At some throttle positions at some revs fuels may well be reduced compared to what the factory settings are (they are on my bike for example). Whether that means it reduces the fuel enough to reduce the actual amount of fuel injected compared a smaller throttle opening I have no idea. Let's say 'sometimes' it might!

In your case you have a lean condition because you have opened the throttle a bit to keep at 3000rpm going up a long hill. That takes more power and so needs more fuel that it is not getting.
You need to raise the needle or fit a different needle.
I'll let somebody who knows CV carbs well get into the detail.

[-SeabrookTrickBagger]

Recently I used my homemade dual a/f meters and O2 sensors to set the a/f mixture on my evolution engine.  It's not fuel injected.  I made these settings during a sustained run at 3,000 rpm on a flat road.  On a road with a sustained climb, at 3,000 rpm my meters showed the engine running leaner than on the flat road.  I'm trying to understand the significance of the throttle position to the mixture.  On efi bikes, what adjustment does the ecm make for throttle position, add fuel, reduce fuel, or what?  Thanks for your input.  

Since there are several aftermarket EFI systems as well as the stock EFI system, one would have to know which EFI system you want to know about.  For example, the Daytona Twin Tech EFI ECU is an alpha n system which measures fuel needs based on throttle position and rpm and barometric pressure (upon initial start up or full time barometric reads depending on how you set it up in parameters).  I think it is accurate to say that the DTT TCFI does not use the mass air flow sensor to determine fuel flow while the stock EFI ECU uses the mass air flow sensor to help determine fuel needs.  As far at the DTT is concerned, as the rpms increase but the throttle position stays the same, the fuel command drops (lower alpha n number).  Decreased load is the difference here.  Also, as the throttle position increases but the rpms remain the same, the fuel command (alpha n number) increases (increased load is the difference here).  Don't read too much into this explanation though since if you looked at a graph showing throttle position percentage and rpm numbers, it will make more sense.  In short, the fuel command on a alpha n system will be higher at 10% throttle position at 2500 rpms than at 10% throttle position at 3000 rpms, and the fuel command at 10% throttle position will be lower at 2500 rpms than it will be at 15% throttle position at 2500 rpms; again, load is the factor.  Higher alpha n numbers mean "more fuel" everything else being equal.

Think of it this way:  how much throttle position increase do you need (hence increased fuel) if you are starting from a standing position and pulling a trailer trying to accelerate at the same rate as if you were not pulling a trailer?  Higher throttle position/increased load, increased fuel needs but all at the same RPMs.

Don't know if that helps, but that is how an alpha n system would read in terms of fuel command/supply.  I don't know how a mass air flow system would read, but anytime you increase the load (effort), it seems to me you need to increase the power which is usually accomplished by adding more fuel ----- no matter what system you use, everything else being equal.

Possibly addressing your issue more directly, your fuel command at 10% throttle position and 3000 rpms would be lower than your throttle position being at 15% at 3000 rpms.  Again, load/effort is the determining factor.

[Evo160K]

Seabrook, PC_Hater,

Thank you for your impressive explanations.  They were both very helpful, I have a better understanding now.  Thank you very much.

[-SeabrookTrickBagger]

Seabrook, PC_Hater,

Thank you for your impressive explanations.  They were both very helpful, I have a better understanding now.  Thank you very much.

You are welcome.

I think you see some advantages and complications of an EFI system.  You have one needle in the carb to account for the varying load conditions all at the same RPM whereas the EFI system might have 20 or more cells (as well as a myriad of other sensors such as engine temp, mass air flow, speed density systems, etc.) which can be individually tuned to change the fuel flow as the rpms and/or throttle position change. By and large, the carb is trying to do all this with just a couple of needles, the throttle plate and the speed and/or volume of the air entering the throttle body which then has to "vaporize" the fuel or at least "atomize" it (which is not a concern on most manifold injected systems much less port injected systems and even less so on combustion chamber injected systems).  Good luck with your project --- as Smokey said:  If you do everything like everyone else, don't expect anything better than what everyone else has.

[Evo160K]

[as Smokey said:  If you do everything like everyone else, don't expect anything better than what everyone else has.

So Smokey said that.  Now I know, I had heard it but had no idea who said it.  Who's Smokey.  Thanks Seabrook, I appreciate your time.

[vanwill]

"Who's Smokey?"   Geez, does that ever make me feel old!  Kinda like the first (and only) time when I asked my son, "Was that regular or microwave popcorn?"

Not screwing with anyone, just realizing how old I am!

[Coasty]

Recently I used my homemade dual a/f meters and O2 sensors to set the a/f mixture on my evolution engine.  It's not fuel injected.  I made these settings during a sustained run at 3,000 rpm on a flat road.  On a road with a sustained climb, at 3,000 rpm my meters showed the engine running leaner than on the flat road.  I'm trying to understand the significance of the throttle position to the mixture.  On efi bikes, what adjustment does the ecm make for throttle position, add fuel, reduce fuel, or what?  Thanks for your input. 

A good article from Nightrider
http://www.nightrider.com/biketech/motorcycle_efi_basics.htm

[Evo160K]

Coasty,

That was a good article.  Thanks very much.

[-SeabrookTrickBagger]

[as Smokey said:  If you do everything like everyone else, don't expect anything better than what everyone else has.

So Smokey said that.  Now I know, I had heard it but had no idea who said it.  Who's Smokey.  Thanks Seabrook, I appreciate your time.

Smokey Yunick