Adjusting Mixture and What's the Stopper on CIS

Tidybuoy · 02:05 PM

I recently replaced manifold gaskets, injector sleeves and 0-rings, vacuum lines, cap, rotor, and plugs. No my engine is slow to start and smells rich.

I still have some work to do before I bring in to a shop and check settings with an exhaust gas analyzer but I would like to adjust the mixture a tad and see what happens.

So, where is the mixture adjustment?

Lastly, on top of my CIS, in-between the fuel distributor and the throttle body, there is a wire type handle and when I look that up in PET, it's listed as a "stopper". Just curious what is this for.

Thanks......Vern

Peter Zimmermann · 02:50 PM

The "stopper" is probably the plug (pull straight up on it and it should come right out) that keeps dirt out of the access to the...mixture adjustment screw. Please, take your car to a shop that's got a properly calibrated CO% machine. Guessing is not the right way to set the mixture, and unless you're measuring both CO & HC you're not getting a clear picture of what's going on with your FI (have you done everything right, when re-connecting the intake runners, etc.?).

Tidybuoy · 12-08-2011, 03:04 PM

Quote:

Originally Posted by Peter Zimmermann

(have you done everything right, when re-connecting the intake runners, etc.?).

As far as I know, I did everything correctly (i.e., cleaned all surfaces, used a torque wrench on runners, new gaskets, etc..).

That said, the car runs pretty well and much better than before. However, it used to start in about 2 seconds and now takes 10-15 seconds. One poster mentioned that the car may have been previously tuned to the vacuum leaks.

I still need to replace the plug wires and I was simply thinking of turning the mixture screw a tiny bit to see if that changes things. I fully plan to have it tuned with the proper equipment. However, before bringing into a shop, I was going to buy the CIS pressure tool and test the various pressures to determine everything is working correctly.

Currently, the car starts but runs a little cold until warmup and I always warm up the car for about 5 minutes before driving. The car runs better after warmup but still has a "bucking" problem between 2k and 3k rpm. As a result, I find myself driving in town in 3rd gear to keep the rpm above 3k. If I get into a stop & go situation, it does not drive well.

Prior to taking to a shop, I want to replace the plug wires, fuel filter and test the acumulator and fuel pump - this is primarily because the car is new to me and I want to know, with certaintee, when tuneup items were done

Joe Bob · Joe Bob's Garage

You can burn a piston purtydamnquick, you betcha.....

Bob Kontak · Bob Kontak's Garage

Quote:

Originally Posted by Tidybuoy

One poster mentioned that the car may have been previously tuned to the vacuum leaks.

Your car should start instantly - like within the two seconds you mentioned.

You did some "damage" during your maintenance activities. Are the wires to the CSV connected? Did you forget to tighten the fat hose to the Auxilary Air Regulator? It is something silly that you did or did not do with the procedures you performed.

You may still have vacuum leaks.

Tidybuoy · 08:22 PM

Ok, Ok....I won't touch the mixture - at least not until I have an exhaust gas analyzer hooked up and a mechanic that knows 911.

That said, I was very careful but I will spend some time this weekend and look everything over.

For the record, the car previously started instantly and now takes 5-10 seconds; it was warm weather then but now it's cold and in the 30's at night. The car previously bucked between 2k and 3k and it still does it. The engine at all other times runs smooth. I am concerned about both the plug wires and the wiring to the distributor. The tack bounces between shifts - it has done that since I've owned the car (about 2 months). When I changed the cap & rotor, one wire in the harness (a ground wire) is very thin and would break if you pulled on it. There are two seperate ground wires in that harness (not sure why) but one needs replacing.

Lastly, when I ordered new plugs, I was not sure which to order as there are 2 listed for '74. I ordered the WR 4 but when I pulled the old plugs they were the WR 5 DC - I'm not sure how that effects engine performance.

Regarding startup time...it takes 5-10 secones only in the morning when ice cold. The rest of the day, even after sitting all day, it starts within a second or two. I may have over dramatized as I simply want it to be perfect, not almost perfect.

T77911S · 12-09-2011, 04:10 AM

WR 4 is too cold. start with WR5 and see how it does. that cold of a plug could be fouling when cold. but you really cant tell about the plugs until timing and mixture are set, and you cant set mixture until you check your fuel pressures, at least i would not pay someone to do it.
i would also check timing and make sure the advance is working.

when i was sorting mine out, i was making mixture adjustments to mine because i new something else was wrong and i was not going to waste money on having it set. in the mean time i learned a lot about CIS and setting mixture on it. i always set mine just on the lean side of surging and the RPMS dropping low when you let off the throttle. when i got my LM2, turns out i was right on.

another thing you can do is reach in the air box and try lifting up or pulling down on the sensor plate. that will make mixture changes that will not mess things up. if it runs better, i would adjust, after all, you have to have someone set it anyway. if you push up and it runs better, it is too lean and needs to be richer. (CW with a long 3mm allen).

Bob Kontak · Bob Kontak's Garage

In post #5 I mention the Aux air regulator for your car. The AAR was not installed until 76. Sorry.

I loaded "bucking" into the search field and came up with a thread where symptoms are similar to yours and the fuel filter was the problem. So as T77 says above "you can't set mixture until you check your fuel pressures"

http://forums.pelicanparts.com/porsche-911-technical-forum/626434-bucking-issue-when-gear.html

Also, for your enjoyment, here is a great thread on 2.7 vacuum line routing.

http://forums.pelicanparts.com/porsche-911-technical-forum/336661-2-7-cis-wur-dizzy-vacuum-lines-routing.html

T77911S · 12-09-2011, 09:02 AM

i dont think that diagram grady posted is correct. the dizzy and WUR look wrong. the WUR should have manifold vacuum. that way the vac goes to zero for WOT to increase the mixture. the dist goes just below the throttle plate, so the vac is removed from the retard as soon as you give it any gas.

Tidybuoy · 12-09-2011, 01:05 PM

Thanks for all the great advice. I definately have some work to do. Still on my list is to replace the fuel filter, get a CIS pressure test kit and test all the pressures, and I'm pretty sure there may be a few more vacuum lines to replace.

Being December, I don't get to spend as much time as I would like on the car but I will definately take the advice above. I figure I really don't need to mess with the mixture (yet). I will get all the other items done first and wittle my way thru it. I also still need to adjust the valves and change the oil but I think by Feb/March I will have gone thru everything.