CIS sensor plate adjustment

[johnco]

got a problem with 74 911s cis sensor plate. from what I have read the correct position of the plate should be near the edge of the taper. Mine is high and I can't adjust it. the lever doesn't even sit on the clip. my idle is rich and kinda rough. when I press down slightly on the plate everything smooths out. warm or cold the sensor height is the same. I can raise the adjustment using the clip but can't lower it. The plate moves smooth and free. I assume it's the 3mm mixture screw holding the plate up but have no CO2 meter and no one checks CO2 for inspection sticker so I can't check that. what's the solution to this problem? Until I get some tech books on CIS I'll have to ask you guys.
Thanks

I don't have the info in front of me but I can recomend a good source for k-jetronic info.

Bosch Service they have a book about $50.00 on service and repair. They also have video tapes on service and repair.
Chris
http://www.boschservice.com/http-docs/access/kjetron.htm

[johnco]

Thanks. I have some books soon. Must be something simple as the engine runs great except for this minor problem. it's not really a big problem but I want the car to run like it was built to run. it starts with just the slightest turn of the key

[stormcrow]

John,

Your sensor plate may be out of adjustment. There is a 3mm adjustment screw between the fuel distributor and throttlebody. Turn it counter clockwise and the sensor plate should start to come down.

If that doesn't solve your problem, then you may have a problem with your fuel pressure going to the fuel distributor.

There are previous posts on the bbs regarding this and there are some pics there to view.

Hope this helps

Steve

[johnco]

thanks. in the last few weeks I've read half the posts on this bbs and working on reading the rest. I assumed it was the 3mm mixture screw but wanted to check here before messing up anything fiddling with the screw. it's very hard to turn and I have a tendency to forget how many turns I've made. I'll try again tomorrow

[john walker's workshop]

the mixture screw does not adjust the sensor plate height. you can tweek the little spring plate inside the air cleaner area to adjust it. push down on the plate and you can see the spring plate move. use a small pair of needle nose pliers to bend it higher or lower. then reset the mix on a CO machine.

[johnco]

tried adjusting the spring. even took the spring out and the plate doesn't drop. I can push it down but it springs back up. I've adjusted plates before years ago on a few 924's I had but nothing works so far on this 911

[wckrause]

You've got something terribly screwed up. The sensor plate is weighted such that it will gently rest on a stop. Something is pulling it up, or something is missing. Do you have a good mechanical drawing of the sensor plate and air box assembly? The Haines manual has a good one.

Do not adjust the mixture screw, that's not your problem.

[johnco]

I've seen many drawings and diagrams but don't see anything missing. the car runs great except for the richness. just a slight pressure on the plate and the idle comes up and it runs so smooth. but even with the spring clip removed the plate stays high in bore when I let off the pressure. same with engine running or not. it's not keeping me from driving but I'd like it to be right. no pops, sputters or backfires. it's just bugging me that it's not right

[wckrause]

Here's the pic out of the Haines manual. The sensor plate should rest on the spring item #14. It's heigth can be adjusted by bending the spring with a pair of needle nose pliers like John Walker mentioned.

I think the spring that you've been messing with is the clip item #15. It won't effect resting heigth.

[johnco]

thanks so much. I'll check that tomorrow

[stormcrow]

John,

Bill is right, the adjusting screw rests on the sensor plate. It may be that the sensor plate piviot which is under the fuel distributor may be gummed up. I know when I disassembled mine, there was a lot of gunk in that area - not sure what it was, or how it got there. That may be the reason your sensor plate won't drop down.

Steve

[wckrause]

Steve,

I think he was expecting to see the sensor plate resting on the stop, rather than on the spring. The spring holds the plate at the right heigth, and allows the sensor plate to spring down against the stop in case of a intake backfire.

[johnco]

I was just trying to adjust the clip instead of the spring plate. thanks for setting me straight,

I can see now said the blind man.