AFR Readings - Carb Tunning - not easy?

You guys can see my engine setup below.

I install a Daytona WEGO III AFR on my bike. I have numbers to share with forum. I am quite surprised with the findings.

The Mikuni RS 34 are setup stock or from factory but for the mains. I upped the mains from 120 to 125.

The needle is in stock spot at -3

The air fuel screw is a 17.5 under a 1/4 turn.

So the numbers are as follows per manufractuer:

IDLE SHOULD BE: 12.8 - 13.5 AFR
IDLE IS: 14.6

PART THROTTLE / CRUISE SHOULD BE: 13.0 - 14.0 AFR
PART THROTTLE / CRUISE IS: 14.5

FULL THROTTLE SHOULD BE: 12.5 - 12.8 AFR
FULL THROTTLE IS: 12.3

I am surprised that these carbs in stock / factory trim, but for mains can handle this setup. Shows that a stock KZ would need to de-tune these bad boys a bunch.

Any questions or thoughts?

Thanks, Spencer

Are you sure about the idle AFR?

14.6 is not very rich...it is almost Stoich(14.7). 14.6 is leaner that your 12.8-13.5 target.

Honestly those numbers don't look too bad at all.

Like tachrev said, that doesn't look terrible.

Your numbers for cruise are a little lean, but the idle is too lean.

The reason you want idle to be slightly on the richer side is so the idle won't climb as the bike heats up. Being richer helps cold idle, and as it warms up the mixture becomes richer than ideal so the idle won't climb as much. Lean idle tends to climb.

There is one thing to remember, if your mixture is so rich that it causes misfire, then there will be unburnt oxygen in the exhaust, which will register as very lean. But you know if that was happening.

ok, that's the numbers that the manufacture recommended.. they were published in the directions.

What would you guys want to see in the fields below? or add others.

Thanks very much.
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Idle:

Part Throttle / cruise:

Full Throttle:

4TheKZ1000 wrote: ok, that's the numbers that the manufacture recommended.. they were published in the directions.

What would you guys want to see in the fields below? or add others.

Thanks very much.

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Idle: 11.5 hot on a hot day, 13 cold but off choke.

1/2 throttle or cruise: 1/2 throttle is acceleration. You could be going over 100mph and accelerate to redline at half throttle so 12.5 to 13.

cruising 50 to 70 mph will be in the 1/16 to 3/16 throttle range.
1/8 throttle cruise: 13 to 14

Full Throttle: manual slide carbs: Starts at 11.5, and swings up as RPMs increase to 13.0 at redline. CV's won't have as wide of a range of swing.

The thing we are saying is lean is your 14.6 idle. You have it marked as 14.6 very rich, but 14.6 is lean, not rich, on old carbureted engines.

Ok, I thought the higher the AFR number the richer? but, lower the number is richer.........

For Example: 11.0 is richer than 14.0 in AFR numbers.

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I put the 17.5 pilot back in and opened the air screw 2 turns. My AFR now toggles between 11.5 to 11.8 on AFR at Idle.

It really smells rich out the exhaust pipe.......is this normal?



Thanks

What do you mean "smells rich" ? Smells like gasoline? That is not normal.

Does it idle perfectly smooth on all four cylinders?
Are all four pipes hot enough to make water dance on them?

Let it idle for awhile and check all four plugs to see if one is different that the others. 11.8 is fine for idle if the bike is fully warmed up and it's a warm to hot day out. The AFR will end up leaner on cooler days with the same setup. But if it smells like gas, you may have a bad carb or fuel setting, or even flaky ignition on that cylinder.

The exhaust smells like gasoline and it is really strong and over powering in the garage.

The carbs are brand new.......only 15 months old.

The Dyna-S will jump a fat blue spark.

All 4 pipes are hot.

not the best Idle at 1100 rpm.......

All plugs have a thick sooty black coat, to rich for some reason.

After checking on ignition, I don't see a problem with it. Is there something I missed? looks good to me. Plugs are dirty.

Condition of Ignition:

Plug wire Ohms checked at 20K
Using 8mm Taylor wires.

1. 0.65 ohms
2. 0.63 ohms
3. 0.61 ohms
4. 0.66 ohms

Battery:

12.7 volts off just sitting
14.2 volts running around 4000 rpm

Coils:

Measured at harness ( yellow - red ) wire.
11.84 volts off not running.
14.43 volts running

At Coil:
14.43 volts on both coils when running.

Spark Plug Used:

NGK B8ES
Gapped at: 0.026

One thing I never did was a sync on the rack, and check numbers. I am going to do this soon.

You are clearly too rich. One thing you have to remember is the afr values are ballpark. Each engine will be slightly different. Lean it out slightly, clean the plugs and do again.

How long were those plugs in the bike?

Those plugs look pretty dark, but not enough to have a bad gasoline smell, and they don't look wet. When I was bracket jetting, I had plugs that looked like that and it still ran fine and there was no strong gasoline smell, even though it was rich.

Is there a chance the gas smell is coming from somewhere else? Airbox or overflow dripping on the exhaust? Or is it directly from the tail pipe?

loudhvx wrote: How long were those plugs in the bike?

Those plugs look pretty dark, but not enough to have a bad gasoline smell, and they don't look wet. When I was bracket jetting, I had plugs that looked like that and it still ran fine and there was no strong gasoline smell, even though it was rich.

Is there a chance the gas smell is coming from somewhere else? Airbox or overflow dripping on the exhaust? Or is it directly from the tail pipe?

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I think what happened is I turned the pilot fuel screw out past its limit. On the RS34 carbs, the fuel screw limit is 1/4 to a 1/2 turn max to the best of my knowledge and what it says in manual. Please confirm if you can.

I turned the pilot fuel screw 2 full turns. It was just dumping loads of fuel into pilot circuit. I noticed looking back on it that the pilot fuel screw became sorta loose after 1 1/2 turns.

The smell is not coming from somewhere else. Coming from tail pipe.

The RS34 have 3 things that affect idle.

1. pilot jet (VM28/486 at 17.5)
2. Pilot air Jet (BS30/97-0.
3. Pilot fuel screw (manual says 1/4 to 1/2 turn)

could #2 be the problem