Mixture adjustment screw?

liverchip · 02-27-2007, 12:18 AM

Hey guys. My 163 motor has the common slide/needle carb. What is the consensus on the function and proper adjustment on the underside-front adjustment screw(the one which needs to be turned with a very short screwdriver).I am running at 3500ft with stock exhaust and 2 turns on this screw. The plug is grey, so I'm assuming she's running lean. I've checked the needle clip position and found it (the clip) at its highest groove(needle farthest inserted). Since very little of my riding thus far has been more than half-throttle, I assume I must richen this puppy up using the clip and that funky screw. Long-winded I know, but what's the consensus on that screw?

cycleway4 · 02-27-2007, 05:52 AM

hi....i would richen it up using the clip....drop it down the needle at least one, maybe 2 positions..............

the idle mixture screw is just what it says.....an IDLE mixture screw....
it will have very little, if any, effect once you touch [open] the throttle.
The idle mixture screw is ported into the idle, slow speed jet, and enters into the engine in front of the slide................the correct operation of this circuit requires the slide being in the closed position.....once the slide is raised, your engine goes to running off the main jet/needle jet fuel circuit

ob1 · 02-27-2007, 08:07 AM

On my Lifan carb, and the Keihin it copies, the idle screw is simply a pin to hold the slide open at a given point to maintain idle speed. The pin rides in a wedge shaped cut on the slide.

Your needle does sound like it is in a lean position. I would place the clip in the center groove then evaluate.

Moving the clip towards the pointy end richens the mixture.

sheadouglas · 02-27-2007, 09:34 AM

Lots of people seem to be adjusting their carb, and moving the clip down. Should I do this if the bike is running just fine? How will I know if I should ever have do this?

fatboy250 · 02-27-2007, 03:22 PM

Quote:

Originally Posted by sheadouglas

Lots of people seem to be adjusting their carb, and moving the clip down. Should I do this if the bike is running just fine? How will I know if I should ever have do this?

If you make any mods to your air filter or exhaust, OR if your's bogs down when you crack the throttle open during slow roll on acceleration. OR if you have backfiring during decel. The old spark plug test is applicable too.

Jason

sheadouglas · 02-27-2007, 03:30 PM

I might get one small backfire or pop at only high RPM's. What I mean is when I run up the RPM's and let off, I get a POP. That's it.

liverchip · 02-27-2007, 04:31 PM

The only reason I'm messing with it is a stumble when moving from idle to wide open throttle.

fatboy250 · 02-28-2007, 09:32 AM

If you've made any mods to increase air flow, you'll need to enrich the mixture. I believe most of these are on the lean side from the factory to meet EPA requirements. So, if you make a mod to increase air flow, it's only gonna get leaner.

Ours are 2 1/2 turns out with K&N type filters and exhaust baffles drilled.

Jason

02-27-2007, 12:18 AM	#1
liverchip Join Date: Nov 2006 Location: Mystery Spot Posts: 1,223	Mixture adjustment screw? Hey guys. My 163 motor has the common slide/needle carb. What is the consensus on the function and proper adjustment on the underside-front adjustment screw(the one which needs to be turned with a very short screwdriver).I am running at 3500ft with stock exhaust and 2 turns on this screw. The plug is grey, so I'm assuming she's running lean. I've checked the needle clip position and found it (the clip) at its highest groove(needle farthest inserted). Since very little of my riding thus far has been more than half-throttle, I assume I must richen this puppy up using the clip and that funky screw. Long-winded I know, but what's the consensus on that screw? __________________ 2009 XR650L Big Red Pig Tusk bar risers 2007 X-Moto(Jetmoto) GY250 --mods--- 15/40 sprockets UNI Pod Filter 2007 Shineray TMS 200XYi--Betsy Betsy Mods:______________________ Acerbis DHH headlight FMF Powercore pipe Uni Pod Filter
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02-27-2007, 05:52 AM	#2
cycleway4 Join Date: Feb 2007 Location: Virginia Posts: 269	hi....i would richen it up using the clip....drop it down the needle at least one, maybe 2 positions.............. the idle mixture screw is just what it says.....an IDLE mixture screw.... it will have very little, if any, effect once you touch [open] the throttle. The idle mixture screw is ported into the idle, slow speed jet, and enters into the engine in front of the slide................the correct operation of this circuit requires the slide being in the closed position.....once the slide is raised, your engine goes to running off the main jet/needle jet fuel circuit __________________ <div>Steve 2006 Roketa DB-07A/RSX-200E 2008 Roketa 250 Scooter 2019 Brozz 250
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02-27-2007, 04:31 PM	#7
liverchip Join Date: Nov 2006 Location: Mystery Spot Posts: 1,223	The only reason I'm messing with it is a stumble when moving from idle to wide open throttle. __________________ 2009 XR650L Big Red Pig Tusk bar risers 2007 X-Moto(Jetmoto) GY250 --mods--- 15/40 sprockets UNI Pod Filter 2007 Shineray TMS 200XYi--Betsy Betsy Mods:______________________ Acerbis DHH headlight FMF Powercore pipe Uni Pod Filter
	0

02-28-2007, 09:32 AM	#8
fatboy250 Join Date: Sep 2006 Location: COLUMBIA, SC Posts: 973	If you've made any mods to increase air flow, you'll need to enrich the mixture. I believe most of these are on the lean side from the factory to meet EPA requirements. So, if you make a mod to increase air flow, it's only gonna get leaner. Ours are 2 1/2 turns out with K&N type filters and exhaust baffles drilled. Jason __________________ 2008 Jonway MC-70-150 2007 Roketa DB-07B (RSM-200E) 2006 Roketa DB-07A (RSX-200E) 1995 Kawasaki Concours (ZG1000)
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02-27-2007, 08:07 AM	#3
ob1 Join Date: Jul 2006 Posts: 499	On my Lifan carb, and the Keihin it copies, the idle screw is simply a pin to hold the slide open at a given point to maintain idle speed. The pin rides in a wedge shaped cut on the slide. Your needle does sound like it is in a lean position. I would place the clip in the center groove then evaluate. Moving the clip towards the pointy end richens the mixture.
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02-27-2007, 09:34 AM	#4
sheadouglas Join Date: Jun 2006 Location: Hattiesburg, Mississippi Posts: 349	Lots of people seem to be adjusting their carb, and moving the clip down. Should I do this if the bike is running just fine? How will I know if I should ever have do this?
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02-27-2007, 03:30 PM	#6
sheadouglas Join Date: Jun 2006 Location: Hattiesburg, Mississippi Posts: 349	I might get one small backfire or pop at only high RPM's. What I mean is when I run up the RPM's and let off, I get a POP. That's it.
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