Trying to adjust idle mixture....

[Bucketlist]

I was motivated to tweak my idle mix due to lean conditions when the engine gets completely warm. With my BL 054 Wur WCP set at 3.65 bar (53psi) it will go lean (+15 afr) after a 30-40 minutes. Lately I’ve had more opportunity to drive the car and the lean condition is getting out of hand.
On my SC Turbo conversion I have the 016 euro fuel distributor which has the removable screw for idle mixture adjustments. My first problem is, with the screw out to make the adjustment there is a vacuum leak thru the hole which makes it impossible to tell the result until the plug is back in the hole. Is this normal with this design?
My second problem, after adjusting the idle mix slightly richer my air fuel numbers dropped into the 9.5 -10.5 ranges only rising to 12-13 when off the throttle. The car runs really good like this and It’s these rich a/f numbers that bother me. When I back off this adjustment very slightly the engine sounds really lean again and air/fuel can bounce from 13.5 – 16. (My adjustments are only about 1/8 turn.)

[gsxrken]

There is a balancing act between initial timing at idle, the idle speed screw, and the fuel head mixture adjustment. If any of them change, idle AFR will change. I’d start with getting your timing right at the correct idle RPM, which is hard to say what it is because the various distributors differ over the years with advance and retard and guys have bypassed a lot of the pierburg switches.
FWIW, I just checked my idle speed screw on the throttle body since my intercooler is on the garage floor at the moment and I’m 3.5ish turns out from full seated. I’ve never heard of a baseline spec for this so take that as one data posing only.

You might also check your intake manifold nut torque- leaning at idle when hot might indicate a vacuum leak somewhere, and a leak there might look rich on boost. Sorry I’m not familiar with the euro fuel head mixture or why tweaking your idle AFR affects your cruise AFR so much. My car would sputter at a true 10AFR.

[RarlyL8]

due to lean conditions when the engine gets completely warm

This indicates a vacuum leak that opens up as the engine warms. As Ken notes the intake is prone to do just this.

[Bucketlist]

Originally Posted by gsxrken

There is a balancing act between initial timing at idle, the idle speed screw, and the fuel head mixture adjustment. If any of them change, idle AFR will change. I’d start with getting your timing right at the correct idle RPM, which is hard to say what it is because the various distributors differ over the years with advance and retard and guys have bypassed a lot of the pierburg switches.
FWIW, I just checked my idle speed screw on the throttle body since my intercooler is on the garage floor at the moment and I’m 3.5ish turns out from full seated. I’ve never heard of a baseline spec for this so take that as one data posing only.

You might also check your intake manifold nut torque- leaning at idle when hot might indicate a vacuum leak somewhere, and a leak there might look rich on boost. Sorry I’m not familiar with the euro fuel head mixture or why tweaking your idle AFR affects your cruise AFR so much. My car would sputter at a true 10AFR.

This thing runs really good at 10 afr which is what has me puzzled and you may be right about the vacuum leak when warm. I thought if my idle speed screw was responsive it would eliminate the vacuum leak possibility but with an intake manifold leak that may not be true. One cylinder could probably affect afr. I will try to check all fasteners with the engine warm and see what I get. May go old school and spray a little brake clean around.
I will also check my timing....I haven't done that in a while.

RarlyL8....being the expert on these old fuel heads is it normal to suck vacuum thru the idle mixture hole when the screw is removed?

[RarlyL8]

There is no idle mixture hole on a fuel distributor. I think you may be referring to the air meter assembly. The early 3.0L turbos did not have the spring loaded stand off. Yes if you remove the cap from the adjustment port it becomes a vacuum leak when the engine is in operation.

[Bucketlist]

Originally Posted by RarlyL8

There is no idle mixture hole on a fuel distributor. I think you may be referring to the air meter assembly. The early 3.0L turbos did not have the spring loaded stand off. Yes if you remove the cap from the adjustment port it becomes a vacuum leak when the engine is in operation.

Ah yes it would be in the air meter assembly, my bad. Thank you for the knowledge, I just wanted to get past that as I search for the problem.

[T77911S]

that doesn't just effect idle. it effects the entire RPM range.

air leak on the pressure will show rich under boost and could go lean at idle.

[Bucketlist]

I spent some time yesterday tightening intake fasteners and spraying some carb cleaner around possible vacuum leak areas but didn't find anything. I tried to check the header pipes with my IR thermometer and found #1 a little cool, #3 somewhat hot compared to the other 4. This may indicate some injector problems, or some other things. My next step, when I get the time, would be the bottle test to check injectors and would expose any problems with torn intercooler seals etc getting to them.

[flightlead404]

Originally Posted by Hot Euro

I spent some time yesterday tightening intake fasteners and spraying some carb cleaner around possible vacuum leak areas but didn't find anything. I tried to check the header pipes with my IR thermometer and found #1 a little cool, #3 somewhat hot compared to the other 4. This may indicate some injector problems, or some other things. My next step, when I get the time, would be the bottle test to check injectors and would expose any problems with torn intercooler seals etc getting to them.

try swapping those two injectors and spark plugs

[Bucketlist]

Originally Posted by flightlead404

try swapping those two injectors and spark plugs

Good idea and might help to understand where to go next.
I've been here before several years ago and did the bottle test then cleaned the injectors as best I could.
I don't know the availability of these old 009 turbo injectors, can I even buy any new ones if needed?

[gumba]

I sent my injectors out a few years back to get cleaned and the spray pattern tested, pretty inexpensive.