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Help...this is simple..right?

Hi All, Help, I need some direction!

930 engine, CIS with Leask WUR, Rebuilt fuel distributor, twin plug with Electromotive ignition
Wide band oxygen sensor and EGT just installed. Recently rebuilt engine

Starts and idles just fine...AFR @ 14, EGT @ 700
Accelerates just fine
Steady state 60 mph 4th gear on interstate AFR between 15.5-16 EGT temp to 1450..way lean
Go to full boost...AFR to 11.5-12 and EGT drops back to 1250-1300, i think just right

I'll tell you, it is strange to get into boost to lower EGT.

So, what is the adjustment to get more fuel at very little throttle? O2 sensor is hooked up.
Thanks, Jim

Old 05-03-2018, 05:08 AM
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What happens if you just richen up your idle, say to 13.50 ?

Perhaps your WUR warm pressures are a bit too high. You can dial it down a bit with leask WUR to richen up your "cruise throttle" You'll need to get pressure gauges out

Lowering the warm pressure will affect idle AFR's too, so you'll need to re adjust accordingly
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Old 05-03-2018, 06:55 AM
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If your CIS air flow meter housing has the 3mm idle CO adjustment post in between the fuel head and the air flow sensor plate try turning the 3mm allen head adjustment screw clockwise a tiny bit.
You have to press the allen wrench down inside the post and gently turn it until it drops down a little farther and engages the allen head screw in there.

Turn it clockwise or to the right for richer and to the left for leaner.
Tiny adjustments have a large effect at idle speed and a very small but still noticeable effect at higher rpms.

When I had an '87 911 turbo with a CIS Flowtech 007 fuel head, 964 cams, and B&B headers it idled smoothest when idle AFR was between 12.8:1 and 13.2:1 after the motor was fully warmed up or after around 20 minutes of driving.
12.8:1 seemed smoothest at idle and steady 65mph cruise on flat Florida interstate was usually around 15:1.
I never had an exhaust temp gauge but did have a VDO cylinder head temp gauge with it's thermocoupler sensor on the #5 spark plug.
The heads warm up fast on these air cooled engines.
Old 05-03-2018, 09:08 AM
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Crotchety Old Bastard
 
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These engines are "fuel cooled" on boost which is part of the reason they are set rich from the factory.
My vote is the idle mixture is too lean, a simple adjustment should do the trick.
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Old 05-03-2018, 09:37 AM
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Thanks all. Looks like consensus is adjust AF ratio when engine is warm to 13 and observe the effect. When these engines are not on the boost they operate like a low compression NA engine. My limited experience remembers NA engine cruising down the highway have EGTs of 600-700 degrees. Is that goal unrealistic? I shall report back. Thanks again. Jim
Old 05-03-2018, 03:18 PM
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It also seems a common tendency to run lean AFR when 'coasting' along. If your engine looks happier with a bit more fuel at idle, that is about as far as you can go with that quirk. You will see the rpm change and engine note alter as you tweek the idle mix. It will get a bit sluggish and lumpy if you go too rich and rpm will drop by approx 100rpm. Go further and it will get worse. but you could possibly tolerate a bit of a trade off. But don't get too fixated on a particular idle AFR - the engines happy spot are all different. Mine is happier around 12.5. If you go richer and engine note gets smoother and rpm picks up you are heading the right way.
Regards
Alan
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Old 05-09-2018, 04:43 PM
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Thanks Alan, I appreciate your response. I did adjust the idle mixture to 12.5 and it made little different in my egt on light throttle. Iím afraid I have vigger problems. See my latest entry saying lambda system not working. Beautiful country that New Zealand. Jim

Old 05-09-2018, 05:11 PM
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