May need to lean out my CIS?
01-24-2002, 11:33 PM
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May need to lean out my CIS?
Hello everyone,
I've been getting 17-18 mpg driving around conservatively, and occasionally I'll notice a puff of black smoke in the rearview mirror if I wind it up to redline. I figured I was running rich, and since I have a 1980SC, I could check what the frequency valve was doing.
Well, apparently a previous owner felt it was a good idea to remove all of the O2 sensor stuff. The control box and frequency valve are gone. Hmmm.
I would assume that since the frequency valve is designed to bleed off fuel pressure in order to keep the mixture in check, that I am running rather rich. I fear that running the engine rich all the time will 'wash' my valve guides, and cause them to wear quickly. Not good.
I thought perhaps leaning out the 3mm mixture screw may help, but that really only effects idle mixture.
Anyone have experience with this?
Can the lack of the frequency valve make that much of a difference?
Any suggestions on what I should do to lean it out? Remove shims from the fuel pressure relief valve?
Any comments are welcome,
Rob Plank
I've been getting 17-18 mpg driving around conservatively, and occasionally I'll notice a puff of black smoke in the rearview mirror if I wind it up to redline. I figured I was running rich, and since I have a 1980SC, I could check what the frequency valve was doing.
Well, apparently a previous owner felt it was a good idea to remove all of the O2 sensor stuff. The control box and frequency valve are gone. Hmmm.
I would assume that since the frequency valve is designed to bleed off fuel pressure in order to keep the mixture in check, that I am running rather rich. I fear that running the engine rich all the time will 'wash' my valve guides, and cause them to wear quickly. Not good.
I thought perhaps leaning out the 3mm mixture screw may help, but that really only effects idle mixture.
Anyone have experience with this?
Can the lack of the frequency valve make that much of a difference?
Any suggestions on what I should do to lean it out? Remove shims from the fuel pressure relief valve?
Any comments are welcome,
Rob Plank
01-25-2002, 09:22 AM
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Join Date: May 2001
Location: Beverly Hills. Mi., USA
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An air/fuel ratio of 14.7/1 is best for economy. This is what your now-removed Lambda system delivered. A ratio of 12.5/1 is best for performance.
You will need an exhaust gas analyzer to check your mixture. I don't recall the reading for the 14.7/1 ratio (it's in a Bentley manual)but the 12.5/1 ratio should be 2.5-3% O2.
You will need an exhaust gas analyzer to check your mixture. I don't recall the reading for the 14.7/1 ratio (it's in a Bentley manual)but the 12.5/1 ratio should be 2.5-3% O2.
