Bike Carb Tuning - using data

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davidimurray

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posted on 9/5/15 at 09:18 PM

Bike Carb Tuning - using data

After a bit of messing around I finally have my carbs (zx6r) just about setup. I've been datalogging a few tests today and think I've just about settled on the needle position in the middle groove. This gives me a cruise AFR around 15 which should be fine with the Duratec.

Below are examples of my tests with the needle in the middle groove and 1 grove down. All comments/advice gratefully received

Middle Groove

Description

1 Groove down

Description

baz-R

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posted on 10/5/15 at 05:40 AM

I'm assuming that the afr reading has no decimal point eg 12.4 = 124?

Are you logging this with a wideband

Its all looking likely to need re jetting and needles to suit your requirements

Most modern engine's will be happy to run lean (14.7 plus) in cruise and light loads. Full loads should be mid 12s and mid 13s in you're idle area if you don't have a cat.

Timing is needed to be set up first as this will effectively change afr

davidimurray

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posted on 10/5/15 at 09:55 AM

quote:
Originally posted by baz-R
I'm assuming that the afr reading has no decimal point eg 12.4 = 124?

Are you logging this with a wideband

Its all looking likely to need re jetting and needles to suit your requirements

Most modern engine's will be happy to run lean (14.7 plus) in cruise and light loads. Full loads should be mid 12s and mid 13s in you're idle area if you don't have a cat.

Timing is needed to be set up first as this will effectively change afr

Yes afr is with a decimal point - megajolt won't log the decimal points! Yes i'm using an AEM wideband.

What areas do you think need work? If you look at the data for middle groove, AFR at idle is mid 13s, at cruise it's 14.3-15 and WOT 12.4 - 13.4.

I'm running 1.5mm mains currently, I have tried 1.4s but they are definitely too small. I've tried the needles in the middle groove, 1 down and 2 down and the setup I've got seems to be the best so far.

At the moment I'm not sure whether it is worth doing any more (car is for road use) and if so I think I need to get into needle reprofiling if I need any more adjustment.

whitestu

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posted on 10/5/15 at 12:18 PM

How does it drive?

I have zx6r carbs on my zetec and am very happy with how well it runs. Mine hasn't been on a rolling road either, but I don't think it could drive much better so if I'm down a few bhp by not being optimised for power I don't really mind as it is plenty fast enough.

Mine has 1.6mm jets with the needle one groove from the top.

I think the zx6 carbs suit a standard tune 2.0 really well as they aren't too big. Mine pulls cleanly from tickoverr in top.

Stu

davidimurray

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posted on 10/5/15 at 12:51 PM

quote:
Originally posted by whitestu
How does it drive?

I have zx6r carbs on my zetec and am very happy with how well it runs. Mine hasn't been on a rolling road either, but I don't think it could drive much better so if I'm down a few bhp by not being optimised for power I don't really mind as it is plenty fast enough.

Mine has 1.6mm jets with the needle one groove from the top.

I think the zx6 carbs suit a standard tune 2.0 really well as they aren't too big. Mine pulls cleanly from tickoverr in top.

Stu

Goes like a train

Setup now with the 1.5mm mains and middle groove is the best yet. More fuel made it feel sluggish and looking at the AFRs they all look to be safe.

alex1991

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posted on 10/5/15 at 03:32 PM

The top graph looks fine.
Would be nice if you could put a bit more fuel in at full load at the very top for safety but should be fine as it is.
Whats the rev limit on the duratec?

baz-R

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posted on 10/5/15 at 03:43 PM

Full load your a bit lean
How are you calculating loads? By the look of the log pattern you must be using tps to calculate load?
Have you had your spark table set on a dyno as you need to do this first as changing it will effectively change afr.

Have a look at megasquirt related afr target tables to give you an idea of how advance and afr needs to change for cruise and load.
I run in the mid 15s cruising with no problems as the engine is lightly loaded but I'm injected
WOT needs to be no richer than 12.4 with the minimum advance that gives you maximum torque output.
The key is if the engine is working hard don't lean it off
Mid to light loads you can back off the fueling.
Cv carbs need to be set with full load first to size main jets then mid loads to set needle heights then tweek screws to sort idle mixture.

[Edited on 10/5/15 by baz-R]

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