930 CO spec - set it by the book, or richer?

[cowtown]

For JW, or other guys with 930s, what mixture spec have you found to be good for these engines?

Is the book spec good, or is it a compromise for low emissions?

[beepbeep]

I've seen different explanations but my understanding is that 930 idle CO-adjustment screw actually does nothing to mixture further on rev band as it only adjusts plungers rest-stop height.

Others will probably chime-in.

[cowtown]

Thanks Beep. Anyone else have an opinion on this?

[john walker's workshop]

3.5-4% works well. just affects the idle, and real low rpm take-offs.

[tiorio]

This has actaully been bugging me, what's the big deal with 930s richening up the mixture with CO adjust then? It's doing effectively nothing after what RPM? How do I richen up the mixture along the entire RPM range?

I haven't done any other research on this lately so forgive my ignorance...

[cowtown]

I'd like to get an answer to that too. I'd never heard of Beep's statement that mixture only counts at low RPM, but I'm open to learning new things. Maybe because the WUR responds to boost (in the form of control pressure drop) through the added rubber line (?)

Anyway, I set mine to 3.6% with my Gunson today (meaning anywhere from 3.0-4.0 I guess) and I'm happy with the performance. I'm going to need a new clutch though

PS - I've got mine running all the way to redline and at full boost now. I have seen the light. I now know what the phrase "Scary Fast" means.

[beepbeep]

What i want to say is that CO-screw in CIS only moves the rest-stop for "barn-door" which measures airflow, so as soon as you step on the gas and more air starts rushing trough the air-flow meter, it lifts from the screw and does it's thing of regulating fuel-flow in the maze.

With other words, it's only determining plungers default position at idle, which in it's turn determines how much fuel goes in. Get my point? It has nothing to do with RPM's but how high barn-door goes back when there is little air-flow (like idling). Screw is nothing but adjustable rest-stop...It won't get the door to open further or anything.

If you want to richen the flow, you need to fiddle with control-pressure. I pasionately hate CIS so i never learned how and why but i vaguely remember that system pressure is to be reduced (yes) to raise fuel flow as whole sheebang is pressure-controlled...i bet someone will explain this better. Jocke?

[john walker's workshop]

the screw does not adjust the "at rest" height of the sensor plate, but finely adjusts the plunger position in the fuel distributor until there's enough fuel for a decent idle. 3.5-4% gives you a nice strong humming idle, different from a weak, sort of rough, missing idle that you would get from way rich or way lean. the 930 WUR richens the mix under boost. if you want richer, get an enrichment device. andial, pelican, etc.

[tiorio]

So ifin I have pinging at high RPM with stock boost/everything else I'm screwed? Can't richen the mixture without buying a third-party solution?

Or do I have some other problem as well (likely I'm sure)...

[Jocke]

I set my 930 little rich, goes around 4.45 in CO but still idle very fine at 700 rpm.

/J

[john walker's workshop]

if there's pinging, retard the timing, or lower the boost if it's above .8bar, until it doesn't. kind of hard to tell, but 930s on boost go from a roar to a raspy sound as soon as pinging starts.