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Hate to do this... 74 CIS with Surging, Skipping, Ect. at 2000ish rpm
I'm sure it is on here somewhere but i cannot find it in the threads. My 1974 is surging around 2000 rpm. Did the starter fluid check on the CIS system and tightened some things... no leaks and no difference... I have a fuel filter on the way.. Love this car, but should I invest in the 5million dollar carb kit?! Any helpful pointers to save me some time? Im sure im not the only one..
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05-02-2013, 07:25 PM
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ROW '78 911 Targa
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Don't be a hater...
 Do an advanced title search on CIS or a google search for CIS Pelican and you will have a lot of reading to do. To test and adjust CIS you really need to have a Bosch CIS fuel pressure tester and either buy a CO meter or have it checked at a garage to adjust your mixture. Surging can becaused by one or multiple items, intake air leak, vacuum hose leaks, mis-adjusted fuel pressures, failing fuel pump or other components, junk in the fuel system, sticky distributor, bad ignition wires, sticky throttle linkages etc.... This thread a good read: Long term & Commonly Neglected Maintenance Do some reading, buy a fuel gauge tester and test the system, check the CO for your mixture and post up your numbers when you have them. A really good ignition tune up with new parts won't hurt either. As Tony will say if he reads this thread, there is nothing so difficult about the CIS system that can't be fixed with simple component trouble shooting, or somethng very similar. I had my car running great with CIS after going through the entire system and havng the right tools to test and adjust, but the tuner geek in me made me install EFI....
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Dennis Euro 1978 SC Targa, SSI's, Dansk 2/1, PMO ITBs, Electric A/C Need a New Wiring Harness? PM or e-mail me. Search for "harnesses" in the classifieds. |
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05-03-2013, 08:14 AM
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76 911S Targa
Join Date: Oct 2010
Location: Idaho
Posts: 1,150
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If you haven't been driving the car during the winter and you are just now driving the car in warm weather, try some injector cleaner to help clean the fuel system. After five hundred miles or so, if it is still surging, then you can look for problems.
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76 911S, 2.7, Bursch Thermal Reactor Replacements, Smog Pump Removed, Magnecors, Silicone Valve Cover Gaskets, 11 Blade Fan, Carrera Oil Cooler, Turbo Tie Rods. |
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05-03-2013, 09:42 AM
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Designer King
Join Date: Mar 2004
Location: Toronto, ON Canada
Posts: 5,499
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Always make sure your ignition components are within spec before you check out the CIS, incl points rotor, cap, plugs and wires. And make sure your distributor is advancing and timing is correct.
EG how are your points? Worn down ones can lead to steady speed missing. If all ignition parts are OK, check for vacuum leaks. After that, check out your fuel and control pressures. Did this condition just start up after winter storage? Did you use fuel stabilizer? Did you do any other recent work to the engine? You don't NEED carbs per se. The CIS is a good, steady, reliable and relatively fuel efficient system. You will get more from the engine w/ carbs, especially if you go w/ a more aggressive cam but will use more fuel.
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Paul Yellow 77 Sunroof Coupe/cork interior; 3.2L SS '80 engine/10.3:1/No O2; Carrera Tensioners; 11 Blade Fan; Turbo tie rods; Bilstein B6; 28 tube Cooler; SSI, Dansk; MSD/Blaster; 16x7" Fuchs/205/50 Firestone Firehawk Indy 500s; PCA/UCR, MID9 Never leave well enough alone Last edited by Paulporsche; 05-03-2013 at 11:09 AM.. |
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05-03-2013, 11:07 AM
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Ok. I bought the car about 2 months ago. I just replaced fuel filter, distributor cap, Distributor internal points, put injector cleaner through it, and used a whole bottle of starter fluid looking for air leaks...
I cannot find any leaks in the CIS system. Checked the plugs and they are white... I am thinking an air fuel mixture issue as it now only happens in 2nd & 3rd gear. Guy had it for over 10 years and only put 5,000 on the newly rebuilt motor. Needless to say the car sat for way to much. I cleaned a whole squirrels nest out of the airbox.... Last edited by Yuppie1974; 05-03-2013 at 05:07 PM.. Reason: More Info |
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05-03-2013, 05:04 PM
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Registered
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Random vacuum leak checks.
Injectors: Rubber/plastic around them can become brittle. A shopvac in the intake pop-off valve and 3 feet of gas hose to listen with will help you hear these leaks. Brake booster hose: These can crack near the transmission and above the transmission support.
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'82 SC 3.0L Targa, Chiffon/Brown “It all began when I was looking around but couldn’t find the car of my dreams anywhere. So I decided to build it myself.” - Ferry Porsche |
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05-03-2013, 05:20 PM
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Registered User
Join Date: Jun 2012
Posts: 1,544
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The hidden problem and often the culprit of mysterious CIS air leaks are the most overlooked and almost never changed or maintained plastic fuel injector sleeves AND their o-rings. These things are super important, and just because they are peened in the runners people shy away from this super-important maintenance issue. Why no one does this when it's all out and being replaced is beyond me. As you can see, I am a huge advocate of changing these all out.
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05-03-2013, 09:16 PM
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ROW '78 911 Targa
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Quote:
Bucking and jumping will happen if you lug these motors. Drive them from 2500 rpm and up. then see if it happens... My car only sees 3rd gear above 35 mph once it's warm and I never go below 2200 rpm when it's cold...
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Dennis Euro 1978 SC Targa, SSI's, Dansk 2/1, PMO ITBs, Electric A/C Need a New Wiring Harness? PM or e-mail me. Search for "harnesses" in the classifieds. Last edited by timmy2; 05-03-2013 at 09:48 PM.. |
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05-03-2013, 09:43 PM
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Registered User
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Welp, when I drive the piss out of her she runs great. Maybe it's user error, either way I don't see anything wrong with some maintenance. I have straights on it right now and am putting stock back on it today. I will check my mixture and inform.
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05-04-2013, 06:45 AM
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1974 Porsche 911
2007 BMW 335xi
Heinz
