what is the ideal AFR for a street bike?

[billyd1]

Hi everyone.

I'm wondering what the ideal air to fuel ratio would be for my '09 RKC. Does the gas mileage decrease as you richen the mixture from the stock setting? I can feel a definite difference in throttle response and power from a cold (enrichened) and warmed up motor. I have a stage 1 upgrade installed, SE air cleaner,Rinehart slip ons and the new super tuner. On my dyno chart the AFR averaged 13.9 or close to that. Any help would be great as this is my first REAL motorcycle :s and I'm unfamiliar with the breed. Thanks!

 

[Bud White]

More fuel = less fuel milage .. 13.9 shouldnt be to bad 14.7 is what they are set at from factory which is way to lean .. so 13.9 richens up a bit but you shouldnt see a huge drop in milage unless your right hand keeps it wound up.. Is it rich enough time will tell but it should be close for cruising .. once you get over 40 or 50% throttle it goes to open loop anyways and richens the mixture way up for getting on it

 

[billyd1]

I just wish there was a way to set the tuner so it would run as good warmed up as it does cold at all throttle settings

 

[rancid]

ideal is somewhere round 10.5:1 at idle 12.5:1 at part throttle/cruise n up to about 13.5- 14:1 at wide open throttle, it is true that fuel consumption will be hurt if its to rich but as hard to believe as it is it will also suffer if its to lean, if you graph fuel consumption versus a/f ratio its a big arc.

 

[relxn88]

ideal is somewhere round 10.5:1 at idle 12.5:1 at part throttle/cruise n up to about 13.5- 14:1 at wide open throttle, it is true that fuel consumption will be hurt if its to rich but as hard to believe as it is it will also suffer if its to lean, if you graph fuel consumption versus a/f ratio its a big arc.

I don't believe this answer is well thought out! Just my 2cents.

 

[relxn88]

may i ask why?
it gives you an idea of were the AFR line should be when dyno'd.
when i dyno i try for around 12-13 in a nice line, the smaller the number the richer the mixture
ie
14.1 AFR is 14.1 parts of air to fuel
13.6 AFR is 13.6 parts of air to fuel meaning richer mixture

hope this helps clarify

This is just my opinion for a Streetbike tune, 1: I believe 10.5afr is to rich for any rpm 2: The idea of part throttle/ cruise is usually meant as the part of the ride to give the best MPG and although Harley trys to keep that at the mid 14's, I usually set the bikes for 14.0afr(give or take .2 depending on the owner's driving habits) 3: WOT @ 14.1 may be great for a car, but the question was asked about a streetbike and the average person doesn't want his engine possibly damaged(over a period of time) due to a lean condition at full throttle to "maybe" gain a minimal amount of hp. I set them up for 12.8-13.0afr for WOT. Streetbike, to me means the owner wants a well balanced tune for his bike that he can ride for years without having to do any major repair work. I may alter the afr slightly to the owners preference and build. I'm sure everybody has their own way of tuning, but this is just the way I do it.

 

[BoomerBob]

With the 02 sensors if you're gonna run below, say 14 or so, then you'll want to pull the sensors and plug the holes unless you want to ruin the sensors. Obviously this doesn't apply to the 20 column of the AFR table so you have some leeway for decel popping and also WOT which most people don't see very often. I'm going by the TTS mastertune which is like the SERT but better.

Using the TTS the AFR needs to be set at 14.6 for the 02 sensors to work.

Where I live in Arizona it can get hot, like 120 hot, in the summer so I may want to run my AFR down to 13.8 or so to get that cooling fuel to my top end. I'm still learning about EFI but I've come quite a ways in the 4 short months I've had my 07. I've got a carbed 99' which is what I've known how to tune for a long time.

 

[BoomerBob]

When you say "switch them off" are you talking about the sensors? You can switch them off by taking it out of 14.6 using the TTS unit but the sensors will still be awash in the exhaust stream. My info comes from Doc in Florida; one of the best tuners in the country according to some. I had a local guy do a dyno tune on my bike but it still wasn't quite right even though it was much better. I talked with Doc since I bought the unit through him, and I sent him my current MAP. He checked it out and sent it back with a lot of corrections. Now my bike runs perfect with just a little burble on decel which is normal.

You bring up a good point though. I guess they could simply be unplugged and cleaned before restoring the 14.6 tune but I'm not sure why they go bad in a rich condition if they aren't being used. I'll have to send an email to Doc and ask him why.

 

[wildspirit97]

With the 02 sensors if you're gonna run below, say 14 or so, then you'll want to pull the sensors and plug the holes unless you want to ruin the sensors. Obviously this doesn't apply to the 20 column of the AFR table so you have some leeway for decel popping and also WOT which most people don't see very often. I'm going by the TTS mastertune which is like the SERT but better.

Using the TTS the AFR needs to be set at 14.6 for the 02 sensors to work.

Where I live in Arizona it can get hot, like 120 hot, in the summer so I may want to run my AFR down to 13.8 or so to get that cooling fuel to my top end. I'm still learning about EFI but I've come quite a ways in the 4 short months I've had my 07. I've got a carbed 99' which is what I've known how to tune for a long time.

The Thundermax W/ Auto Tune uses Oxygen sensors, and Just about every map they have starts at 13.8:1. I've been running it for about a year now and have no problem with oxygen sensors going bad. I have my cruise AFR set to 14.2:1 under normal circumstances. If my head temp hits 285 or above it'll richen it up to 13.8:1. I have the Idle set at 13.8:1 and WOT drops down to about 12:1.
The ThunderMax replace the stock narrow band oxygen sensors with wide band. I don't know what difference that would make, but if your gonna be talking to your source again in the near future I'de be curious to hear what he had to say about that.

 

[glider]

When you say "switch them off" are you talking about the sensors? You can switch them off by taking it out of 14.6 using the TTS unit but the sensors will still be awash in the exhaust stream. My info comes from Doc in Florida; one of the best tuners in the country according to some. I had a local guy do a dyno tune on my bike but it still wasn't quite right even though it was much better. I talked with Doc since I bought the unit through him, and I sent him my current MAP. He checked it out and sent it back with a lot of corrections. Not my bike runs perfect with just a little burble on decel which is normal.

You bring up a good point though. I guess they could simply be unplugged and cleaned before restoring the 14.6 tune but I'm not sure why they go bad in a rich condition if they aren't being used. I'll have to send an email to Doc and ask him why.

You can contact Doc through the forum links. He is notified when he gets a PM.

Harley Davidson Community