79 Euro - setting the idle

[Rupesy]

I finally got my fuel tester from JC Whitney and did a few tests. I found that my fuel pressure was 75 psi, pressure decay test checked out fine. Outside temp was around 65F and tech spec book says control pressure should be 23 psi and mine read 30 psi. Tapped the post for the bimetallic switch in the WUR down about 0.15mm and it dropped control pressure it down to about 25 psi. (This made a noticeable improvement on warmup) I watched it rise over the next minute or two to 52 psi where it leveled out. According to the tech spec this is where it should be. I pulled my spark plug and it was white which usually means you are running too lean. I noticed it has been running a little lean over the past week or so. You may remember when I bought the car I posted a pic and it was encrusted with solid deposits. So step in the right direction anyway. I have been trying to set the mixture screw and idle screw to get somewhere in the neighborhood of 900 rpm. When I set the mixture screw lean, I can fine tune the idle down to 900 no problem, but then I run lean and thats no fun. If I richen the mixture up, it seems like it performs really well, but I can't set the idle below 1100 rpm. If I try to go below that, the engine goes into that oscillation cycle. Any tips or more tests to do? Whay does it oscillate like that?

[MPDano]

How about your ignition timing? Where is it at right now?

[devilinblack]

The oscillation or "hunting" as you'll see it referenced as in the CIS threads usually mean that it's too rich. When you're adjusting the idle you have to adjust the air set screw as well as the mixture screw. If you just turn the idle down, you're decreasing the air that can get past the plate, but using the same amount of fuel so it will then become rich. To decrease the idle turn the idle down and then lean the mixture out, but remember to always turn lean to rich. Confused yet? The way I understand it you need to go too lean, then richen it just a hair because they spec that all adjustments be made lean to rich.

I could also be wrong about all this, but this is what I seem to recall reading and what has worked for me. But it's getting late and I'm overly tired.

If you want the Bosch CIS book as a PDF let me know and I'll post it for you. I also found these threads helpful.
http://forums.pelicanparts.com/showthread.php?t=232089&highlight=cis
http://forums.pelicanparts.com/showthread.php?t=185926&pp=20&highlight=cis+mixture+idle

[Rupesy]

Thanks for the links on setting the mixture. I'm going to have to read through them a few times. I will check the timing tonight and report back. I was turning 1/4 and 1/2 turns. I see I may need to have a smaller turn like 1/8 to get it dialed in. I might have gone a little too rich on the last turn as the idle is not so steady. However, it does move throught he higher rpms better.

A quick question on control pressure from the WUR. Mine is currenlty at 52 psi which seems to be about right according to the tech specs and a couple of Bosch manuals I have. I read a WUR fix pdf document that said to set it between 40-46 psi? Any comments? That would definitely change things with mixture setting.

Thanks

[DPW928]

The A/F adjustment is extremely sensitive and requires small incremental changes. Did you try the lean to rich halfway point plus 2 or 3 degrees rich method of adjustment? If you get the A/F adjusted correctly and the idle still wants to flucuate, look for another vacuum leak.

If your control and system pressures are in the range on the chart you should be OK. What you don't want is a system pressure being at one end of the range and control pressure being at another end. i.e. if control is at the low end of the range and system is at the high end of the range, you will run too rich.

The idle bypass screw allows metered air to bypass the throttleplate so it has no bearing on the A/F ratio.

Dennis

[Rupesy]

I just might be too rich now. Checked timing tonight and was 31 BTDC @3000 rpm as the book says it should be. I put in all new spark plugs also. Will report back tonight.