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 Post subject: Idle A/F
 Post Posted: Wed Apr 18, 2012 12:14 pm 
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I've got a Racepak Sportsman with an O2 installed and was wondering if I can do some tuning in the garage. I'd like to get the idle much leaner, I've had enough of the burning eyes. Can I work on just the idle without making passes? If yes, what numbers should I shoot for? This is on race gas.


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 Post subject: Re: Idle A/F
 Post Posted: Wed Apr 18, 2012 3:01 pm 
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14ish but mine is right at 15.......See if you can lean it out with just the mixture screws and if not move the IAB 5# at a time...

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 Post subject: Re: Idle A/F
 Post Posted: Wed Apr 18, 2012 3:21 pm 
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Ron I'd shoot for idle AFRs of at least 13.0/13.5 to start and work up from there until it wants to die. And BTW, this needs to be set with it in gear at idle too. I've got mine in the upper 13s now and I've seen it at over 15 on the return road at part throttle. If it gets a stumble in it then it's too lean. ;-)

Bottom line is that each engine will want something a little different and all these numbers should only be used as a reference.

Your mileage may vary. ;-)

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 Post subject: Re: Idle A/F
 Post Posted: Wed Apr 18, 2012 4:57 pm 
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The AFR thats displayed by any wideband of the idle of a full race engine is a useless number to use for anything. There is soo much unused oxygen and raw fuel going out the exhaust ports that the wideband is a useless tool for measuring and setting idle. Tuning is best done by feel and experience.


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 Post subject: Re: Idle A/F
 Post Posted: Wed Apr 18, 2012 5:45 pm 
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Ron, one thing I forgot to mention is that my O2 sensor bungs (8 of them) are mounted about 12 to 14 inches down the pipe from the head. If you're trying to read one mounted in the collector then you need to put an extension on it to keep clean air from sucking back up and making those AFR readings show even leaner than it might be.

As for shrinker's comment, a wideband "may" not be that accurate as he says but I NEVER use any one tuning aid as gospel! Experience, plug reading, seat of the pants and your own senses all play a part in this and no single one of them will be a do all fix all.

Your mileage may vary!

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 Post subject: Re: Idle A/F
 Post Posted: Wed Apr 18, 2012 9:52 pm 
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Thanks guys,
My sensor is about 21 inches from open air. Greg Kelly told me I needed at least 16 to be good.
5 numbers seems like a big jump, but I'll try it.


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 Post subject: Re: Idle A/F
 Post Posted: Thu Apr 19, 2012 5:46 am 
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IMO the best test is little to no RPM change from Neutral to in gear back to neutral.
If it's very far off there will be a significant change in RPM.


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 Post subject: Re: Idle A/F
 Post Posted: Thu Apr 19, 2012 2:46 pm 
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Scott Smith wrote:
IMO the best test is little to no RPM change from Neutral to in gear back to neutral.
If it's very far off there will be a significant change in RPM.

Scott, you're saying that the A/F, at idle, is right when the rpm's don't move much going from N to 1st, right?


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 Post subject: Re: Idle A/F
 Post Posted: Thu Apr 19, 2012 7:07 pm 
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Yep


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