62 replies to this topic

[jaydee]

Mate, the only time a new build have to run at idle, is when you bed in the camshaft at its first start up, and you do that idling at 2k-3.5k rpm

You need to put load on it, thats where you get the actual vacuum from the engine, also the depression in the carb is different under load

No point of letting it idle and watching the AFR gauge going up and down, you can potentially flood the engine and glaze the bores...

[colinu]

Jaydee - I bedded the cam in just fine at 2500rpm. Now I want to make sure the mixture is OK enough (leanish and stable) so I don't risk bore wash when I run the engine in. Advice I'm getting here based on the AFR bounce and 'throttle blip/stall' is there's still something wrong... i.e. I'm still nervous to take her out on the road.

Bizarly... if I hadn't have fitted an AFR gauge then I would have 'tuned by ear' and got around the throttle blip/stall by setting idle a little high and adjusting the mixture a tad on the lean side.

 

Edited by colinu, 22 July 2013 - 11:08 PM.

[colinu]

Ahh sorry thought you were talking cables. I ditched the old silicone vac pipe/tube as it kinked too easily. I'll double check to make sure there are no kinks/splits/leaks on the new one I'm using.

[Gulfclubby]

I'm beginnging to think your gauge is dodgy.

My dad has an AFR in his Cooper and that almost always reads at full rich, yet when you look at the plugs after a drive, they're greyish brown as they should be, car idles fine, runs fine etc, all in order. It's just the AFR that is reading off.

[Gulfclubby]

It's just a vertical bar that goes from red (lean) to green to red (rich), and it always reads full rich or one bar below that and only ever blips down to green on shifts.

I haven't ever touched it, so I have no idea how it was set up. I like my minis where the blinker relay is the most complicated electrical component.

[conrod]

At times like this I resort to pulling the carb off and replacing it with a (known entity) borrowed carb or a spare you might have just to test if that is where the problem lies. I do the same with ignition problems. It helps to have spares in the cupboards. Saves time and a lot of guesswork. If it runs slightly better then you are on the right track. Alternatively you could run your carb on a mates car and see if the problem happens on their car. Then you will know it is the carb....

[jaydee]

It's just a vertical bar that goes from red (lean) to green to red (rich), and it always reads full rich or one bar below that and only ever blips down to green on shifts.

I haven't ever touched it, so I have no idea how it was set up. I like my minis where the blinker relay is the most complicated electrical component.

 

Then its a narrow band gauge and pretty normal that you get these readings, its not a problem in the sensor itself, its just the gauge. You need a pretty expensive one to get an accurate reading of those voltage variations

There was a in-depth discussion about this on turbo-minis a while ago

[colinu]

Update... (and some videos below)
Boredom or rather frustration with the carb/mix got me 'tinkering' in other areas. I checked the cam timing and it was pretty much spot on at 106deg (correct for this ACD-RS+), retorqued cylinder head nuts, and readjusted tappet clearances to 15thou. Tweaked around with carb mix and idle again and it's idling a little better if 100rpm higher than it should (and doesn't seem quite so prone to try stalling if I blip the throttle). AFR is a bit more stable too. I do still need a little choke to get it started (even in this warm Californian weather).
With the exception of stripping the head off and measuring the compression ratio I've checked out pretty much ever possible cause of this problem... can't find any evidence of air leaks in the inlet/carb/manifold, have swapped in another HIF44 which made no change, timing/megajolt are all OK, etc.

So for those in the know (and preferably who run wideband O2 gauges) what do these videos tell you? Am I close enough to being able to take this on the road and run the engine in, or is the mixture still too rich/erratic?

[jaydee]

You need to get these readings under load, doesnt look too bad at idle

[colinu]

I was hoping that'd be the case. OK, I have a week or so of work to complete (arches, paint, electrics, interior, suspension geometry) then I'll take it out on the road and check the readings out under load. Stay tuned...

[ACDodd]

I'd say that AFR gauge is useless at Idle. It sounds little lean to me. This is why I recommend a gas analyser for idle emmissions. You should find the afr gauges works alot better with constand higher rpm exhaust flow. If it still jumps around you need a better one!
 

[Earwax]

Colin u ,,   i agree with AC.   I have a bosch sensor on a innovate AFR gauge and idle is the least accurate, at the tailpipe too much air flow contamination ( get lean readings) and at the bung just aft of the manifold joins it can be erratic.

 

If you are confident, put it on the road, and do a plug check ..... go for a drive keep constant rpm (say 3500) and then cut engine and  glide to halt , and then check plugs.   I did this a couple of times to gain confidence in the AFR readings. 

[colinu]

Thanks for the latest replies... my confidence has been boosted :)
AC - I'm still trying to get my paws on a working emissions analyzer as I definitely want to verify approx 3.5% before any serious attempt at running in. If I can't find one then I'll make a pit stop into my nearest garage (just around the corner) and see if they'll let me put the Mini on theirs for 20mins.

[ACDodd]

Aim for 2 to 2.5% at idle. I would go straight round to your local garage, in offer some cash for a few minutes fiddling and put your mind at rest. Quick simple, sorted.

 

AC

[cal844]

Aim for 2 to 2.5% at idle. I would go straight round to your local garage, in offer some cash for a few minutes fiddling and put your mind at rest. Quick simple, sorted.

 

AC

+1. i'm lucky, i have access to all this equipment ;)