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Simple carb question:

  • Thread starter Thread starter uudfourty
  • Start date Start date
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uudfourty

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CV Carbs:

Air mixture screw-- turning the screw in reduces air. True or false?
 
uudfourty said:
CV Carbs:

Air mixture screw-- turning the screw in reduces air. True or false?
Click to expand...
On CVs you are actually dealing with fuel, not air. Turning the screw in leans the mix and out richens. Starting point is usually about 1 1/2 turns from lightly seated, I mean very lightly.
 
I think for CV carbs it's called idle mixture screw or fuel mixture screw. It controls the fuel at idle not the air. I've never seen a CV carb with an air screw.
So turning the idel screw in would make ther mixture leaner.
So, answer is flase.
 
What Billy said...except more like 3 turns for the fuel currently in use.
 
No wonder I started backfiring after I sealed my airbox.

6.5 turns out on each of 'em.

PO gloriously stripped the head on number 4 to a nice "Y" rather than an "l" . Weaksauce. I guess I'll be for getting some PB this afternoon.

Thanks fellas.
 
uudfourty said:
No wonder I started backfiring after I sealed my airbox.

6.5 turns out on each of 'em.

PO gloriously stripped the head on number 4 to a nice "Y" rather than an "l" . Weaksauce. I guess I'll be for getting some PB this afternoon.

Thanks fellas.
Click to expand...

i sooooo started that up here in jersey. definately. by the way, 6.5 turns is a lot.
 
Yeah, I heard it from a co-worker a couple of years ago, so it must've been on TV or something.

6.5 was a lot... quite a lot, but at 3, I'm still backfiring.

No backfire before sealing the airbox.

I'll have valve shims and a set of merc sticks a week from today.
In the meantime, I'd love to not backfire every time I accelerate after deceleration.

I'll crank it down to 2 turns from lightly seated and see what happens.
 
Two turns is a good point to start with, then do your tweaking for highest rpm when the engine is warm. You may end up at 3 anyway, but it should run well enough at 2.
Stock settings may have been anywhere between 1 to 1 1/2, so 2 is an improvement on that.

Back to your original question, and to add some detail to previous answers...the proper term for the adjustment screw is "idle mixture adjustment screw". Note that it says "mixture" in the description. The mixture ratio is controlled by the pilot air jet in the carb intake throat and the pilot jet which is down in the float bowl, next to the main jet. The mixture screw merely adjusts how much of this mixture is allowed to pass into the carb output throat.

Based on that description, the answer to your original question is "yes, but...". It does reduce the amount of air, but it is air that is already mixed with fuel. 8-[

.
 
Steve said:
...the proper term for the adjustment screw is "idle mixture adjustment screw".
Click to expand...


That'd be why I didn't have a lot of luck with the search feature, then.

I'll crank it back to 2 or so tomorrow before I head out and see what happens.
 
Somewhat related question: Does that screw have any affect on the fuel mixture when actually riding the bike or is it just idle?
 
bleeble said:
Somewhat related question: Does that screw have any affect on the fuel mixture when actually riding the bike or is it just idle?
Click to expand...
Any time you are using the idle circuit, which would be through about 1/4 throttle.
Basically, any riding in the city where you are not playing Ricky Racer. 8-[

If you mark your throttle as if you are getting ready to do plug chops, you can see just how far you are actually moving the throttle for a particular speed.
It might surprise you just how little you move that grip. :shock:

IMG_3646.jpg
 
You have other problems besides the idle mixture screws. Leaky airbox? Valves need adjusted?
 
Oh yeah. I've always got other problems.

Sealed up the airbox last weekend, and thats when I started running mega rich and backfiring.

Shims get here in a week.
 
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