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Old 09-06-2000, 10:51 AM   #1
Scooby Newbie
Member#: 1992
Join Date: Jul 2000
Location: Port Jefferson, LI
Question too lean with carbon deposit on exhaust.... help????

Okay, when I've been getting carbon black powder on my exhaust tip, not alot but enough that i notice, I thought i was running rich (thats one of the signs, right)?? so when i set up the S-afc with blue wire mod it said that my O2 voltage with no correction was .72. I have to richen it up to +20% at 6000rpms to get a .85 at WOT. Is this normal, how can i be getting black carbon if i was lean.???? its a MY99 RS with weapon R intake W/ K&N filter and a Scoobysport Exhaust + UR Pulley.
Please help..thanks
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Old 09-06-2000, 10:57 AM   #2
Matt Monson
Scooby Guru
Member#: 832
Join Date: Jan 2000
Chapter/Region: RMIC
Location: Teh Ghetto Garage, CO
99 2.5RS, '85 911
'73 914 and 2012 BRZ


I'm no expert here and drive a MY00, but am going to speculate and let others confirm or deny my thoughts.
So, it is lean up top, but is it rich at idle? It could be running rich at some other point in the powerband. But now that you have an AFC you should be able to dial it in.
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Old 09-06-2000, 11:04 AM   #3
Scooby Specialist
Member#: 759
Join Date: Jan 2000
Chapter/Region: NESIC
Location: Warwick, RI
2012 Regal GS
2000 SV650


I have a JC Sports intake and Rallispec N1 exhaust and also get carbon deposites. There is no way the computer can make the A/F ratio perfect all the time, and I would prefer to have it err on the rich side for safety reasons. Anything that burns puts off smoke, so there should be a little bit of carbon there anyway. I also get a bit of carbon residue on the bumper, but when corrected ~22% on the top end for the intake the A/F ratio looks good, so I am going to leave thigns alone. I wouldn't be worried until the back of the car is black!
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Old 09-06-2000, 11:34 AM   #4
Scooby Newbie
Member#: 1992
Join Date: Jul 2000
Location: Port Jefferson, LI

Thanks guys, i was worried i did something wrong..it scared me to have it corrected +20%. but i guess its okay......

I guess my next investment wil be an EGT.
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