Air screw adjustment on carb zen

gopa99 · 15th June 2009, 19:13

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??

Jaggu · 15th June 2009, 21:46

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.

techn0l0gist · 16th June 2009, 01:21

Quote:

Originally Posted by Jaggu

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.

techn0l0gist · 16th June 2009, 04:42

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)

buddy · 30th June 2009, 12:46

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.

sgiitk · 30th June 2009, 14:45

@buddy: There is no hard and fast rule. Each car has its own ideal.

Jaggu · 30th June 2009, 20:06

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.

15th June 2009, 19:13	#1
gopa99 BHPian Join Date: May 2009 Location: Bangalore,Kochi Posts: 334 Thanked: 203 Times View My Garage	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??
	() Thanks

15th June 2009, 21:46	#2
Jaggu Team-BHP Support Join Date: May 2004 Location: Bangalore Posts: 20,215 Thanked: 15,904 Times	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.
	() Thanks

16th June 2009, 04:42	#4
techn0l0gist BHPian Join Date: Aug 2004 Location: Goa Posts: 364 Thanked: 89 Times	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) Attached Thumbnails
	() Thanks

30th June 2009, 12:46	#5
buddy Newbie Join Date: Nov 2006 Location: Delhi Posts: 7 Thanked: 0 Times	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.
	() Thanks

30th June 2009, 14:45	#6
sgiitk BANNED Join Date: Dec 2007 Location: Gurugram Posts: 7,969 Thanked: 4,788 Times	@buddy: There is no hard and fast rule. Each car has its own ideal.
	() Thanks

30th June 2009, 20:06	#7
Jaggu Team-BHP Support Join Date: May 2004 Location: Bangalore Posts: 20,215 Thanked: 15,904 Times	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.
	() Thanks