Ideal AFR for highway cruising for economy

[dom14]

Hey Guys,

What is the ideal AFR for my RB30 carby on highway for economy, rather than power?

Currently cruising AFR on 60-70km/h is around 12:1, too rich obviously, hence the apparent reason for poor fuel economy and soot.
Not sure, how to go about fixing it, but reckon some carby fiddling involved(and hopefully not the jets )

Above is on petrol. Dunno about LPG yet, 'cos the wideband I bought need to connect to a PC to change the fuel type, and I
haven't got the correct adapter for that, yet. It's a real bummer, 'cos if I knew early, I would've bought a one that doesn't need
a PC connection to change fuel type.

Thanx in advance for any advice.

Dom

[garett]

14.7 would be the one i'd move it to and see, should be good for economy but you will lose power. i always tune the carby by the seat of the pants feeling, gas i use a lamba value.
don't make it too lean.

14.7 is the ideal but close to it would be alright. i've always run my carby's on the rich side for a bit more go.

you should have a mixture screw on the carby, small movements on this until you find the correct reading

[dom14]

14.7 would be the one i'd move it to and see, should be good for economy but you will lose power. i always tune the carby by the seat of the pants feeling, gas i use a lamba value.
don't make it too lean.

14.7 is the ideal but close to it would be alright. i've always run my carby's on the rich side for a bit more go.

you should have a mixture screw on the carby, small movements on this until you find the correct reading

Hi mate,

Yes, I used the mixture screw to get idle mixture to 14.7, which is good, but as you know, that has little or no effect on half or wot throttle when cruising or revving for power. I guess(meaning I don't know ), when revving high on WOT for power, mixture getting rich is ok?
Cruising AFR is 12 or less. Do you reckon that's not good for economy? (My guess is it is probably not?)
If I wanna fix that to closer to 14.7, how would you go about it, with a RB30 Nikki carby?
The secondary throttle valve doesn't get stuck. Secondary throttle valve is vacuum operated(rather than mechanically operated) in this Nikki carby.

Any tips from you, I would be grateful.

Thanx
Dom

[dom14]

I haven't got to the LPG tuning yet.

One reason is 'cos I don't have the correct adapter to connect the gauge to a PC(It uses serial port, new computers don't have it,
so I need to USB to serial converter adapter, the old laptop I have doesn't work with the Innovate software, I dunno why)

The other reason is that I wanted to make sure I get the petrol side of AFR tuning right first, before I get to LPG.

[threedogs]

In the days of old tuning a carb by "ear" meant turning the mixture screw say
clock wise till it spluttered, then you turned it anti clockwise counting the turns
till it spluttered. Then you would calculate how many turns divide that in half.
that was your sweet spot.
or

Rev it to 2000rpm turning the screw [mixture] you could hear the "sweet" spot
very easily,,,,,,,,,lol

Remember you'll never get economy and performance at the same time

[dom14]

In the days of old tuning a carb by "ear" meant turning the mixture screw say
clock wise till it spluttered, then you turned it anti clockwise counting the turns
till it spluttered. Then you would calculate how many turns divide that in half.
that was your sweet spot.
or

Rev it to 2000rpm turning the screw [mixture] you could hear the "sweet" spot
very easily,,,,,,,,,lol

Remember you'll never get economy and performance at the same time

Thanx mate.

Yes, and I'm only aiming at economy atm on both idling and cruising. It it get rich a little bit on WOT, I'm ok with that,
'cos I think that's way it suppose to be, but cruising AFR of 12 or less is probably not ideal for me atm.

There's a backyard carby tuning procedure for RB30 in Gregory's manual. Basically, I turn the mixture screw all the way in until it seats, the back down anti clockwise four turns or so. Then adjust the rpm to 800. Then keep turning the screw in until I get the highest idling rpm. Stop the mixture screw at that spot &
set the idling rpm to 800 or so using idle speed screw. The engine has to be warmed up before the above.

Now, I don't need to do that 'cos of the wideband gauge.

I'll try the mixture screw technique above and see how it goes.
I didn't try it before, 'cos i was told at cruising and above, idle mixture screw doesn't play an vital part in AFR.
Another thing I thought about was that even if the idle mixture screw affect the cruising AFR, I would still have to find a
happy medium between idling AFR & cruising AFR by turning the mixture screw.
I hope I won't have to, and hopefully can keep idling AFR & cruising AFR as separate settings.

Thanx
Dom

[NissanGQ4.2]

I haven't got to the LPG tuning yet.

One reason is 'cos I don't have the correct adapter to connect the gauge to a PC(It uses serial port, new computers don't have it,
so I need to USB to serial converter adapter, the old laptop I have doesn't work with the Innovate software, I dunno why)

The other reason is that I wanted to make sure I get the petrol side of AFR tuning right first, before I get to LPG.

What operating system on the laptop and have you a link 2 the Innovate software?????

[dom14]

What operating system on the laptop and have you a link 2 the Innovate software?????

The software says it's compatible with Win2k to Win10, so I'm assuming it's a 32bit software application. My desktop has no serial port, but an old laptop does(winxp), but the software demands to upgrade to
DotNet 4, which refuses to install DotNet4 in the end of the installation. I haven't had a chance to muck around with the old laptop software issues to find out
the exact reason. So, I'm waiting to get hold of a USB to serial adapter which I haven't had a chance due to Easter weekend.

This is Innovate website link to the software.

http://www.innovatemotorsports.com/support.php

It refuses to install saying it needs DotNet 4, and then DotNet 4 Installation craps itself in the middle.

[dom14]

Innovate software application installs fine on my Windows 7 machine. It's a 32 bit software application.

[dom14]

Carby's obviously had issues with idle circuit as well. Today it's running AFR 10 on idling, which indicates it's not just cruising throttle issue.
It's running rich like hell on idling, and the mixture screw does not respond at all.
Carby's getting heaps of petrol into the intake via something other than idle circuit, I think.
I wonder what that is!!!