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Old 15th June 2009, 19:13   #1
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Default Air screw adjustment on carb zen

Hi

could any body help me with airscrew adjustment on a carb zen? Does the screw tightening make the mixture rich? I was told opposite views by 2 MUL technicians here in bangalore, now sort of confused!!

I though believe that air screw loosen means 'lean' and air screw tighten means 'rich'!! Help me guys!

Also i read that air screw adjustment with gas analyser is to be done at high RPM's to realise best effeciency (average running RPM, but not at idle), and what practise followed by the workshops (idle setting) is actuallly wrong!! any comments from core techies, if any in here??
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Old 15th June 2009, 21:46   #2
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Screw out will lean the mixture. As far as i understand its the idle circuit, and tuning at a lil raised idle (200-300 rpm more) is the right way to set it correct. Helps in correcting the flat spots that come during the transition from idle to main circuits. At higher revs and very high revs main jets take over which doesnt have any air screw effect.
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Old 16th June 2009, 01:21   #3
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Quote:
Originally Posted by Jaggu View Post
Screw out will lean the mixture.
It is actually the opposite,even I used to think the same way earlier, however tightening it will make it lean

quotes from the service manual, all workshops follow this method, the exhaust gas analyzer is used optionally as the last step to fine tune the idle mixture screw :

Note that the procedure below is for the G13 engine which came with the esteem/gypsy, since the mikuni carb is almost the same for the zen, i guess tuning procedure should be the same.
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Last edited by techn0l0gist : 16th June 2009 at 01:28.
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Old 16th June 2009, 04:42   #4
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continued from prev post - this is the last step in the adjustment procedure (the values for CO below are for the models without catcon, for the catcon equipped models, I think they'd be 0.5-1.00)
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Old 30th June 2009, 12:46   #5
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Hi techn0l0gist, Can you please tell me the exact number of turns, after full tighteninig of screw that will result in best power & mileage ratio.
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Old 30th June 2009, 14:45   #6
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@buddy: There is no hard and fast rule. Each car has its own ideal.
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Old 30th June 2009, 20:06   #7
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Oops my bad thanks for the correction technologist, i was thinking from a slider carb set up

One method to set it right is, adjust the RPM to max using idle screw (slightly raised RPM helps) and from that point, 1/2 turn towards richer side. Very crude but works most often.

Right approach is using a gas analyzer.
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