Afr on tickover
Turbo Mini Forums

Gents , had the mini running , afr gauge is now up and working , managed to get it ticking over but mixture screw wound right in ( full clockwise ) but still showing 16-17 on the gauge !!

Does it tick over reliably ?

What plugs are you using ?

Air leak on the inlet maybe?

Is the lean off etc blocked on the carb?

In the 13's at last!.. Just

What happens when you pull the choke out? Does that richen it up? I seem to remember if the sensor is not properly plugged into the gauge but the gauge is powered it shows 17, mind you it should be coughing like buggery with the screw fully in......

Edited by oli79 on 29th Dec, 2015.

On 5th Oct, 2014 Shauna said:
What that's crazy, you go commando hahaha! How heavy is your helmet ?

Pull the dashpot off, make sure the screw is raising and lowering the jet

On 5th Oct, 2014 Shauna said:
What that's crazy, you go commando hahaha! How heavy is your helmet ?

Does it idle well? Cos it would be rough at 16 or 17 if it ran at all. Any over run or backfires?

Edited by Sprocket on 29th Dec, 2015.

Where is the sensor placed, and what wideband ?

Presumably it's a known working unit ?

As others say if it actually was around 16-17, it'd be idling like crap.

Edited by stevieturbo on 29th Dec, 2015.

9.85 @ 145mph
202mph standing mile
speed didn't kill me, but taxation probably will

Bpr7es if I remember correctly ,
lean off blocked off
Was right into 17+ at first and wouldn't tick over well at all .
Choke out definitely helps but still leaks fuel when the choke is on !
It ticks over ok at 1100 rpm at that.
If you try give it any throttle obviously gasps and try's to stall but past that it revs up fine
Il check the jet is moving
No backfires or anything or run on
Gauge is a brand new aem
Lambda is located at the front of the floor just after the bottom of the down pipe

Edited by cossierick on 30th Dec, 2015.

I second this, check jet height with the dashpot off and check the needle is set in the piston correctly.

Also make sure the float valve is closing off propperly. While you have the dashpot of, turn the fuel pump on. There should be no fuel flow out the top of the jet.

Edited by Sprocket on 30th Dec, 2015.

Jet moving up and down ok . Il check fuel in 5

do a simple vacuum leak check grab a can of carb cleaner or similar highly flammable stuff and carefully with an extinguisher handy spray the joining parts, hoses ect if there is a leak it will raise the rpm

Leak check done , all seams fine .

I've had a brain wave though ! The carb is a secondhand one due to problems with my old one , now I removed the needle that it came with and put my needle in it . Mine has been filed for my motor , now I do understand that in a different carb it won't be the same but I thought it was still a better starting point than a random one.

Now the one that came out someone has filed a flat spot on it ! It's at the thickest part of the needle . Now could this be that someone else had problems that it was too lean on full rich mixture and did that to compensate ??? Would that work ?

There are two sizes of jet and a huge array of needles. A filed flat on the needle indicates that it has been done to increase the richness, obviousky the thickest (top) part is idle through to cruse, with the thinnest (bottom) part cruse through to full throttle.

Not saying it is as its been a while since i worked with an su carb, but may it be possible that the carb on the car has a smaller jet than the carb you took off? Not even sure its possible....... off to check the book

That makes sense then Colin , and to my thinking is the secondhand carb I have someone has had this same problem hence the filed flat needle

Ok, cant find the book at hand, but....

In general, the HIF44 has a 0.100" jet (~2.5mm) and generally uses needles with the 'B' prefix. The HIF38 generally has a 0.090" jet (~2.3mm) and generally uses needles with the 'A' prefix. Needles are interchabgeable between jets, but obvoisly the 'B' needles are thicker at the top than the 'A' needles.

Id be worried if the jet in the carb is the smaller 0.090", which if we are suggesting the carb is a HIF44, the jet has been replaced incorrectly at some time in the past. The only other conclusion is that the carb is actually a HIF38 and the previous owner used a HIF44 needle

An uknown carb can be just that.

Make sure the jet is the larger 0.100" jobbie and then make sure the needle is in tge common sizes in use to eliminate those as the cause.

Edited by stevieturbo on 30th Dec, 2015.

9.85 @ 145mph
202mph standing mile
speed didn't kill me, but taxation probably will

To be honest when you explain it like that Colin it seams less likely that that has happened but il check tomorrow !


Stevie , I have got problems with it leaking fuel when the choke it's on ! No it definitely shouldn't but I've replaced the choke seals on more than one occasion and even swapped the carb !! I've checked fuel pressure at the carb and that only reads 3.5 psi so that's ok ! I've no idea. I wish I could ditch it !