Air Fuel Ratio

[skelly]

Hi everyone.

I have just fitted an AEM wideband lambda sensor and AFR gauge to my katana so that I can get my fuel injection setup a little better.

I have to say, its a pukka piece of kit with super fast response time.

I have tidied up the bottom end fueling no end and the bike is starting to run real clean now,

However..

I'm curious, what kind of AFR do these old air cooled engines like ?

I was going to go for around 13.5:1 on cruise and around 12.5:1 over 50% throttle mainly for a better full power mixture and to try to keep things cool also.

Anyone have any other ideas on this ?

Cheers.

Skelly.

[Reinhoud]

Somewhere around 13:1 should be fine..

[Blower1]

I have supercharged and fuel injected EFE. Idle AFR is around 13;1, cruise 14 :1- 14.5:1 and over 40% throttle 12:1.

I have tried to go leaner than 14.5:1 when cruising, but engine don´t run nicely.

[Arttu]

Yep, pretty much like @Blower1 said. Idle whatever the engine seems to like, usually around 13:1 with these old engines. For cruise you can go as lean as the engine keeps running cleanly. Again, limit seems to be around 14.5:1 based on my experiences. Any leaner will cause misfires, hesitation and surging. For full throttle and N/A engine I would use something like 13-13.5:1.

[Reinhoud]

You two are brave men..

 

[Gixer1460]

2 minutes ago, Reinhoud said:

You two are brave men..

 

Why? 13.2 : 1 AFR is correct max power mixture - 14.7 : 1 is chemically correct total burn mixture. Using ratios below 12 : 1 IMO is unnecessary if the limitations of the fuel / ignition were understood and compensated for.

[Reinhoud]

I'm surprised a bike runs ok at 14.5, althought that's almost the theoretical ideal ratio.

Ususally you go a bit richer to keep the engine a bit cooler, to save the pistons..

[Reinhoud]

Or does an injected engine runs better on a leaner mixture than a carbureted one?

 

[Gixer1460]

7 hours ago, Reinhoud said:

Or does an injected engine runs better on a leaner mixture than a carbureted one?

 

At idle and cruise when airflow is low ie. relatively closed throttle, the benefit of exactly metered and atomised injected fuel certainly helps. My turbo used to run low of 12.5 : 1 AFR with a static CR of 9.5 : 1 and upto two bar boost. Admittedly using high octane fuel, intercooler and 3D mapped Ignition - allowed 42 deg timing off boost / cruise condition ...... as I said you don't have to use band aids with the correct 'stuff' 

[skelly]

Ok, 

Some interesting points.

My engine is naturally aspirated with an EFE head and Wiseco 1170 kit.

I put some white paint markers on my throttle twist at 25%, 50% & 75%.

As far as the ignition goes, it is quite advanced at light throttle openings, then backs off as you wind it up and the cylinder pressures increase, then advances again up to V max.

The fueling so far is around 13.5 on tickover then around 14.2 up to around 20% RPM, throttle and after that it richens up progressively to around 12.8 at maximum rpm and velocity.

I must say its quite a challenge to keep an eye on the throttle markers, AFR gauge,  and the road when at high throttle openings and the bike is accelerating like mad, and I'm not bigging it up or anything but it is bloody fast.

So far these numbers seem to work pretty well, I deffo get what some of you guys have said about rich mixtures on boosted bikes but in my case slightly leaner works ok and the response is good.

I still have a couple of spots to address, for example at 4K and around 10% throttle it is very rich, 10:1, so I'll sort that and a bit of work on the throttle transients but overall I'm mega happy with it.

[Arttu]

10 hours ago, Reinhoud said:

I'm surprised a bike runs ok at 14.5, althought that's almost the theoretical ideal ratio.

Ususally you go a bit richer to keep the engine a bit cooler, to save the pistons..

On cruise the engine makes quite little power and therefore also heat so there isn't any need to cool it with rich mixture.

Theoretically fuel injected engine could be able to use leaner mixture due to better fuel atomization. But I think difference is minimal at cruise rpm since carbs should do pretty good job there as well. On low rpm difference can be bigger. But what actually makes difference is adjustability. With fuel injection you can adjust fueling quite precisely for every and each operating point of the engine. And that allows tuning to leanest possible mixture on all cruise areas. With carbs the adjustments are always more or less compromise and to avoid hiccups you need to err on rich side.

[Arttu]

1 hour ago, skelly said:

I must say its quite a challenge to keep an eye on the throttle markers, AFR gauge,  and the road when at high throttle openings and the bike is accelerating like mad, and I'm not bigging it up or anything but it is bloody fast.

Oh, really? Have you heard about data logging?