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Registered
Join Date: Mar 2006
Location: Colorado
Posts: 24
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cis/vacuum advance
Hi,
I have been struggling with my CIS hunting for idle once the car gets warm. I have worked to eliminate any air leaks and felt that I had gotten them all, yet today once the car (77 Euro 3.0 pre-lambda CIS) warmed up the loping or hunting continued 1000rpm to about 200 and then back up again. I continued looking for air leaks etc. While in this process I disconnected the vacuum advance and the rpm immediately rose to almost 2500 with no lope. I adjusted the rpm down to 1000 and took the car for a drive-it ran beautifully and actually seemed to have more umph. The car will idle quite smootly (and accelerate and with no problems noted on deacceleration as well) now with the vacuum advance disconnected. So my question is: what is the problem? Is the timing that off or ??? If I plug the vacuum line leaving the distributor the loping begins again, if I plug the line to the distributor nothing changes (duh) and if I apply vacuum (that sounds better than suck on) to the line leading to the distributor the engine speed drops (as it should). Any suggestions??
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77 Euro Carrera 3.0 67 Lotus Europa vintage race car 76 MGB 60 Bugeye waiting in the wings assorted toyotas and fords |
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09-23-2006, 12:06 PM
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Registered
Join Date: Dec 2004
Location: Novato, CA
Posts: 3,064
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Is this the advance biscuit with two vacuum connections (advance & retard), or advance only?
Quote:
ianc
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BMW 135i. Nice. Fast. But no 911... "I will tell you there is a big difference between driving money and driving blood, sweat and tears." - PorscheGuy79 |
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09-23-2006, 01:59 PM
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It's not a vacuum advance. It is a vacuum retard.
it is only supposed to retard timing ~5° at idle. W/o the dist vacuum line connected you should see ~0° (TDC) timing, connected at idle that will go to ~5° ATDC (retard). The dist vac. is pulled from a port that sees vacuum at idle but when the throttle is cracked the vacuum drops and the timing advances to that dictated by the mechanical advance(which hopefully is free to function correctly)
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Bill Verburg '76 Carrera 3.6RS(nee C3/hotrod), '95 993RS/CS(clone) | Pelican Home |Rennlist Wheels |Rennlist Brakes | |
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09-23-2006, 02:11 PM
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Registered
Join Date: Mar 2006
Location: Colorado
Posts: 24
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The distributor only has a single vacuum line coming off of it.
What I meant when I said when I plug the line coming from the distributor nothing happens, what I mean was when I plug the line that goes directly into the distributor (and nowhere else from this end) nothing changes-which should be the case because there is no vacuum coming from the distributor so obviously nothing would happen, because nothing is being changed-it was just kindof a dumb statement of the obvious. Chris
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77 Euro Carrera 3.0 67 Lotus Europa vintage race car 76 MGB 60 Bugeye waiting in the wings assorted toyotas and fords |
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09-23-2006, 02:35 PM
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Registered
Join Date: Jun 2003
Location: Camarillo, Ca.
Posts: 2,418
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There may be a leak in the advance unit that is open only in a certain position making the advance change and a vacuum leak. Find a vac pump with a gauge to check for the leak at the diaphragm.
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Aaron.  F.S. 1965 Solex engine w carbs/cleanerBurnham Performance https://www.instagram.com/burnhamperformance/ |
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09-23-2006, 03:31 PM
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1976 Porsche Carrera 3.0
1995 Porsche 993 Carrera Coupe
