Base setting of mixture for CIS 1980SC?

[scottsc]

I have just had my faulty fuel distributor rebuilt by rebuiltsystems due to a massive over-fueling issue. Report from them stated O-rings were all broken and hard.
This has now solved the problem with the FD however I don't know what to set the base mixture setting to as I had moved the original setting while diagnosing the fault.
There were no starting issues with the car before the FD stuffed up. Now it will only run if I lift the sensor plate up a bit while cranking but it seems to be running way too rich, lots of white smoke and when I drop the plate it will cut out. The pressures are all within spec;
System 75psi
Control cold 28psi
Control warm 45psi
Also how much would you turn the hex screw to make changes, by the millimeter or 1/4 of a turn?

Help would be appreciated!
Scott

[Daviboy]

Good thread worth the read and lots more if you search CIS Idle Speed and Mixture Setting Without an Analyzer

[timmy2]

I am going to type this out for you as I can't get a good picture from my Service Manual. Not word for word and you don't need to bleed your lines.....
From:
Basic Adjustment of Mixture Control Screw after Replacement of Operating Lever

1. Pull injectors with lines attached and place in clear jars to see fuel flow.

2. turn mixture screw 1-2 full turns counter-clockwise

3.Turn on ignition and pull the safety switch or jumper the fuel pump relay socket to force pump to run.

4. Turn the mixture screw clockwise until the injectors just begin to eject fuel, then turn screw back 1/2 turn counter clockwise.

5. Run engine to full operating temperature and adjust idle speed and CO level to their specified values.

That is all they give.

Hope it helps.

[scottsc]

Thanks guys. I will give it a go now i have something to go by.

Scott.

[scottsc]

I have done the steps timmy2 has posted and I had to screw the mixture screw clockwise about two full turns before injectors started to inject, then backed off 1/2 turn. Now injectors start to inject when you just slightly lift the plate. This should work now. However I noticed the injectors were slightly dripping before injecting. Does this mean they are bad? Possibly got gunk in them from the bad FD.

Scott.

[ManniB]

Scott,

the fuel injectors should not drip at all when the pressure is below the opening pressure. Recently I have checked all of mine; they were dry below 3.5 bar (if memory serves me right) and started spraying in a nice pattern one the pressure rose above that value. That was after I soaked them in fuel injection cleaner for several days. I didn't test them before, so they may have leaked or not.

- Manfred

[scottsc]

Originally Posted by ManniB

Scott,

the fuel injectors should not drip at all when the pressure is below the opening pressure. Recently I have checked all of mine; they were dry below 3.5 bar (if memory serves me right) and started spraying in a nice pattern one the pressure rose above that value. That was after I soaked them in fuel injection cleaner for several days. I didn't test them before, so they may have leaked or not.

- Manfred

Sounds like I may need to invest in a new set of injectors too! I had these soaking in thinners and back flushed them also. They seemed to spray OK but I hadn't noticed them leaking until now.

Scott.

[boyt911sc]

Originally Posted by ManniB

Scott,

the fuel injectors should not drip at all when the pressure is below the opening pressure. Recently I have checked all of mine; they were dry below 3.5 bar (if memory serves me right) and started spraying in a nice pattern one the pressure rose above that value. That was after I soaked them in fuel injection cleaner for several days. I didn't test them before, so they may have leaked or not.

- Manfred

Manfred,

Multiple tests of 100+ CIS injectors' for operating pressure (psi) were recorded at 35 psi. (minimum) up and to 50+ psi. The new ones opened between 35 - 40 psi while the older units registered 45 - 50 psi. Anything over 55 psi go to the dumpster. The critical requirement is the uniform mist-like spray pattern during injection. Injectors with jet stream pattern should be discarded.

Operating pressure, spray pattern, volumetric flow, and no-leak (during stand-by) are what I expect from these injectors. So I segregate these fuel injectors into different groups:
Group I: (35 - 40) psi.
Group II: (41 - 45) psi.
Group III: (46 - 51) psi.

Group IV: ( less than 55 psi) saved.
Anything over 55 psi go to the dumpster.

I've been using these reference values as a personal choice and others might prefer something different.

Tony

[boyt911sc]

Originally Posted by scottsc

Sounds like I may need to invest in a new set of injectors too! I had these soaking in thinners and back flushed them also. They seemed to spray OK but I hadn't noticed them leaking until now.

Scott.

Scott,

I have several sets of fuel injectors that were tested and guaranteed to work. No surprises. $110 for six (6) injectors shipped to continental USA. I still have your address. PM me.

Tony

[scottsc]

Originally Posted by boyt911sc

Scott,

I have several sets of fuel injectors that were tested and guaranteed to work. No surprises. $110 for six (6) injectors shipped to continental USA. I still have your address. PM me.

Tony

Hi Tony,

Thanks for the reply. YES! My car is finally running now I have set the base mixture.
However I have found after about a minute of running there is still a lot of white smoke being emitted, un-burnt fuel. So this maybe because of the leaky injectors I guess? Seems to run and rev OK though. I have backed off the mixture screw hoping this will reduce the fuel thereby the smoke but it still continues to emit.

Anymore suggestions?
Scott

[timmy2]

How long has the car been sitting without running.
It is fairly normal to get a lot of white smoke after sitting for a few weeks. It should clear up with a good run. "Italian tuneup"...

Do you have a CO tester?
Buy or borrow a Gunson tester and set your mixture, idle and CO to spec once you are at full operating temperature after a good 20 minute highway drive.

[elviaduxc]

That was after I soaked them in fuel injection cleaner for several days. I didn't test them before, so they may have leaked or not.

[scottsc]

Originally Posted by timmy2

How long has the car been sitting without running.
It is fairly normal to get a lot of white smoke after sitting for a few weeks. It should clear up with a good run. "Italian tuneup"...

Do you have a CO tester?
Buy or borrow a Gunson tester and set your mixture, idle and CO to spec once you are at full operating temperature after a good 20 minute highway drive.

Yes Dennis I was thinking of doing this but I am waiting until it's dark so the smoke can't be seen as easily! The car has been sitting for nearly 3 months and that was after the last time it ran with bucket loads of fuel being dumped in by the faulty FD. I thought there maybe some sort of CO meter you can buy in a kit form or something, using an O2 sensor and some electronics? Anyway time for a drive and hopefully burn some CO off into the atmosphere!

Scott.

[ManniB]

Originally Posted by scottsc

Hi Tony,

Thanks for the reply. YES! My car is finally running now I have set the base mixture.
However I have found after about a minute of running there is still a lot of white smoke being emitted, un-burnt fuel. So this maybe because of the leaky injectors I guess? Seems to run and rev OK though. I have backed off the mixture screw hoping this will reduce the fuel thereby the smoke but it still continues to emit.

Anymore suggestions?
Scott

I'm not compeletely sure, but the fact that your injectors leak shouldn't be a problem once the engine is running. Remember that the CIS is a constant injection system which means the injectors do spray 100% of the time anyway. Dripping becomes a problem when the engine is switched off since it continues to dump fuel into the intakes and cases the residual fuel pressure to drop.

- Manfred

[scottsc]

I've now been for a spin and started to smile again feeling that Porsche power again until I looked behind to see a fog of smoke enveloping a number of streets in my suburb! Sorry neighbours!
I got it up to operating temperature then I stopped and leaned the mixture screw off about another half a turn from the initial 1/4 turn from the base setting guide while the engine was still running. So about 3/4 of a turn and the idle dropped back to about 1000rpm which is what it was originally before the fault occurred with the FD. The smoke reduced but hasn't completely gone but I stopped backing off the mixture at this point as I felt the engine was starting to run not quite as smooth.
My question is, will dripping injectors cause engine smoke as they are constantly injecting anyway so would slight leakage make that much difference?

Scott.

[scottsc]

Originally Posted by ManniB

I'm not compeletely sure, but the fact that your injectors leak shouldn't be a problem once the engine is running. Remember that the CIS is a constant injection system which means the injectors do spray 100% of the time anyway. Dripping becomes a problem when the engine is switched off since it continues to dump fuel into the intakes and cases the residual fuel pressure to drop.

- Manfred

Thanks Manfred. You must have read my mind. I will do some more driving tomorrow night and see if it clears. I had only just replaced the oil but I might have to change it again as it has a strong smell of fuel now.

Scott.

[scottsc]

Just changed the oil as it was contaminated with fuel and after another good drive all smoke has cleared and car is running good. Thanks to all for the help and advice.

[ManniB]

Originally Posted by scottsc

Just changed the oil as it was contaminated with fuel and after another good drive all smoke has cleared and car is running good. Thanks to all for the help and advice.

Great news, enjoy driving her!!!

- Manfred

[boyt911sc]

Originally Posted by scottsc

I've now been for a spin and started to smile again feeling that Porsche power again until I looked behind to see a fog of smoke enveloping a number of streets in my suburb! Sorry neighbours!
I got it up to operating temperature then I stopped and leaned the mixture screw off about another half a turn from the initial 1/4 turn from the base setting guide while the engine was still running. So about 3/4 of a turn and the idle dropped back to about 1000rpm which is what it was originally before the fault occurred with the FD. The smoke reduced but hasn't completely gone but I stopped backing off the mixture at this point as I felt the engine was starting to run not quite as smooth.
My question is, will dripping injectors cause engine smoke as they are constantly injecting anyway so would slight leakage make that much difference?

Scott.

Scott,

Leaking fuel injector/s would have a dramatic effect for starting and depends how much fuel was dumped into the cylinder. Once you are able to start the engine, the excess fuel would eventually be consumed by the subsequent combustion in the cylinders. How easy could you get the engine to start (cold)? Have you checked the spray patterns of the six (6) injectors?

You have to determined if the smoke generated was produced due to excess fuel (mixture) or engine oil being burned.? Drive the car for 20 - 30 mins. a couple of times and observed if the smoke has changed.

I had experienced a severe smoking from a newly rebuilt engine that was discouraging to see. My garage was covered with white smoke and was worried my neighbor would call the fire department. I was doing an engine start-up with the engine installed in my engine test stand and took me a lot of start-ups (running) to eliminate the smoke.

BTW, if you were closed to the optimum fuel mixture setting, it would need very small amount of adjustment. This is a very sensitive adjustment and requires very small movement of the screw. I always discouraged or warned people not tinker the fuel mixture setting. That would the last thing I do and I'm pretty much happy with my work.

Keep us posted.

Tony

[timmy2]

Just changed the oil as it was contaminated with fuel and after another good drive all smoke has cleared and car is running good. Thanks to all for the help and advice.

I'm happy for you, enjoy!