FI Idle Mixture Screw

[Manfred]

I was just wondering where the FI Idle Mixture screw was on my 1978 westy FI system.

26 is the idle speed screw. 25 is the Idle Mixture Screw. I'm guessing the Idle Mixture screw is the one next to the air flow sensor (damn I can't find a picture of it). It not far from the air cleaner looking down at the engine.

[chitwnvw]

It's a big standard screw at the bottom of the S boot, directly to the right of your accelerator cable. It's near where your vacuum hose for your distributor should be attached. It's about the size of a nickel, you can't miss it.

[Amskeptic]

I was just wondering where the FI Idle Mixture screw was on my 1978 westy FI system.

On top of the AFM to your left. It is a gate for unmetered air. Lift the gate and you get more unmetered air. That leans it out. You "unscrew" the screw to lift the gate, i.e. COUNTER-clockwise leans the mixture. It is either a simple slot or a 5mm allen.

The speed screw uses the same principle. It is a gate. "Unscrew" lifts the gate and allows "uncontrolled" air into the engine, i.e. counter-clockwise raise the engine speed.
Colin

[Manfred]

I was just wondering where the FI Idle Mixture screw was on my 1978 westy FI system.

On top of the AFM to your left. It is a gate for unmetered air. Lift the gate and you get more unmetered air. That leans it out. You "unscrew" the screw to lift the gate, i.e. COUNTER-clockwise leans the mixture. It is either a simple slot or a 5mm allen.

The speed screw uses the same principle. It is a gate. "Unscrew" lifts the gate and allows "uncontrolled" air into the engine, i.e. counter-clockwise raise the engine speed.
Colin

Great. I turned this screw by accident a while back when I was having double relay issues. My blundering maybe why my idle is so off.

[Manfred]

Ok so I found a huge vacuum leak and was able to dial in my idle with this mixture screw. FYI for anyone that has never messed with this screw, when you change the mixture you will also change the idle.

I'm not sure the correct way to dial idle in, but maybe Colin or someone else can put in their 2 cents.

I increased/decreased my mixture until the engine smoothed out, then I adjusted the idle using the idle speed screw.

Comments?

PS I don't believe the Bentley called this the idle mixture screw. I think they referred to it as the CO2 adjustment or something. They do not give any instructions other than adjusting it until the CO2 in the exhaust reaches the required emissions level in your state or something close to that.

[Gypsie]

Now use the 'swiper test method' AKA "Colins's Method" to see where idle mix and High rpm mix is.

There are severeal threads devoted to these adjustments.

Now that you have corrected a 'major vacuum leak' the high end may be out of whack as well. That would concern me because I wouldn't wnat to be tooling around at high rpms with a too lean condition and torch the exhaust valves or sumpin'.

Couple of sessions with your afm and you'll be a natch.