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dvderlm

idle rpm

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dvderlm

Is it better to idle at 1050 rpm with 15:1 AFR

or 950rpm with 14.2:1  AFR ?

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dvderlm

So I think 10% more air flows through at 1050rpm versus 950rpm and carries more fuel despite being leaner mixture..

 

At !5.1 AFR there's hardly any CO but some NO2.

At 14.2 there's 2% CO I think.

 

At 15 it'll be quite hot-running too.

 

Wonder if I can get to a happy midpoint? It's eluded me so far twiddling mixture and speed. Perhaps one more idle bypass valve needs opening as well?

Slowest smooth idle and high vacuum is my usual goal.

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Pete1

If you're only talking about those AFR's at idle, not across the range, then I don't think NOx or hot running will be an issue, as there's not enough fuel getting burned to cause high temperatures.  

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dvderlm

True,  but I don't expect the fan to come on in February and it did. Queue was not that awful and I turned engine off a few times before when at red lights.

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dvderlm

Thought I had got it better than 14.2 like 14.4 by opening an idle  bypass valve on cylinder 2 which had highest vacuum with engine not quite fully hot and perhaps 900rpm.

But with headlights and windscreen blower on after a journey idle speed slowed and went richer.

So adjusted again and now at 14.9 to 15.2 and 1050rpm... It's almost as if there's something none analogue involved either side of 1000rpm.

 

I wonder if the Amethyst is doing something at that speed?

Edited by dvderlm
heating blower not rad fan

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dvderlm

www.aldonamethyst.co.uk/Resources.htm

v1.80 firmware "No vacuum advance applied below 1,000RPM, and vacuum advance tapered off between 1,500RPM and 1,000RPM."

 

That will be it I think

So increase the static advance from 500 to 1000 by 1 degree?

 

Maybe I can upgrade the firmware to v1.11.0 which "Vacuum display now includes tapering off below 1,500RPM" so I can see the true taper effect..

 

 

 

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dvderlm

Pushed advance at 500rpm to 8 with 1000rpm at 9. degrees plus the vac advance , which improved a bit.

Then offset the whole map by 1 degree and it has smoothed out. 

Idle mixture screws in a bit, speed screw out to reach 750 and still ticks over.

 

Settled on 950rpm and 14.9:1 AFR. 

Not fully warm but that is encouraging. Amethyst says it is running at 16 degrees advance.

 

Twin carbs need more. 

Need to measure with a timing liight... I think it actually had only 10 degrees advance by the gun last time.

 

The +1 offset means Max Total Advance is now 1 + 5+32 = 38.  

 

 

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Edited by dvderlm

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dvderlm

Here's the "centrifugal" advance curve if anyone is using another programmable ignition.

centgraph.png.f3801a191ab2598ac593588f3dfafe62.png

Edited by dvderlm

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dvderlm

The graph does not show the +1 offset...

or the 5 static

or the vacuum related extra advance which is quite crude as this is the turbo Amethyst.

 

One day...

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Pete1

Nice work man. :smile:

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dvderlm

Actually drove it some distance today without any queues. Felt like 28 days after a massive epidemic 😁 and before the zombie hordes 💀.

 

Once really hot idle had hit over 1000rpm on the over-reading dash tacho so loosened the speed screw about 1/8th of a turn and it is now great. Probably 900rpm.

 

Anyway, that is the smoothest it has felt in motion for ages. Pulling away does not stumble any more below 1300rpm, which I'd kind of got used to. Exiting roundabouts gently is now possible in 3rd gear, speed bumps (which I still dread due to lowness) can be approached and glided over with no clutch slipping.

 

Hope it survives until the Rolling Road day. There's an MOT to get through first.

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