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Mixture adjusting nut...which way?

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G

grandson

Freshman Member
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OK guys..I'm going crazy here trying to figure out which way to turn this nut at the bottom of the SU carb. Looking down at the carbs from the driver's side (left) of the car or the side of the engine where the carbs are, I've been turning the nut clockwise or to the right to lean the mixture. As far as I can tell this unscrews the nut or lets it out thereby leaning the mixture. Is this correct?
 
I'm having difficulty picturing which way you're turning but I think you're going the wrong way.
Think about it like this.
If you're unscrewing the nut then you are lowering the jet which takes the jet further down the metering needle toward the skinny end which lets more fuel into the carb thus richening the mixture.
 
OK Mark...let me try to describe it this way. Standing beside the car and looking down at the carbs, I am turning the nut to my right or toward the firewall assuming this is making it leaner. With the summer heat, I'm finding that as the engine gets hotter, my revs are dropping from 600 or so down to 400. From some research as to what is causing this, I read that the mixture is too rich and needs to be leaned out. Thanks for response...
 
/ubbthreads/images/graemlins/savewave.gif.-FWIW---Keoke Just go the other way until the RPM peaks. /ubbthreads/images/graemlins/confused.gif
 
Now I see it... But I'm still a little confused. If you're turning the leading edge of the nut to the firewall, you'd be raising the nut (tightening) wich would be leaner but your first description it sounded like you were unscrewing the nut. What model SU is this? I've seen quite a few but my hands on experience extends to HS2s and HS4s only.
 
I feel kind of silly getting into this discussion. So many answers already. Looking down at the nut from the top of the carb, turning the nut clockwise unscrews, lowers, the nut & its jet to a smaller position on the needle taper & makes the mixture richer.
D
 
Dave I agree. Is there a possible mix-up between slow idle screw and jet screw on the initial post?
 
Dave, that's exactly what I was trying to say. I'm just saying it badly.
 
[ QUOTE ]
Dave I agree. Is there a possible mix-up between slow idle screw and jet screw on the initial post?

[/ QUOTE ]
Tracy,
I hope not. He DOES say "nut on the bottom". When turning a fastener, the terms left & right & front & back will never take the place of clockwise, what happens when all clocks are digital? Even then we have to define the direction from which we are viewing. Heaven help us when there are no more clocks with hands. I guess we can go to the magnetic flux rules. With the right hand thumb pointing toward the screw top, the fingers point in a clockwise direction. Opposite with the thumb pointing toward the bottom of the screw. "Sort of in jest but not completely".
D
 
I can just see the future.

"United 255, traffic at 11 o'clock, three miles".

"Uh, Center, you'll have to explain that. We've all got digital watches".

Scary thought. /ubbthreads/images/graemlins/shocked.gif
Jeff
 
"United 255, traffic at 330 Degrees Incremental, three miles".

See...it's easy without a clock!
By the way, I'm wearing a digital Timex Expedition right now that has an electronic compas in it.
One of my favorite terms (frequently seen in British text) is "anti-clockwise" (I wonder if there is "anti-counterclockwise"?)
 
HI All I was under the impression he had an HS carburetor he was trying to set up{ Nut on the Bottom}-???-Keoke /ubbthreads/images/graemlins/confused.gif
 
By jove, I think I've got it. This is a triple HS4 set up so from the serious replies above, tightening or raising the nut = leaner and loosening or lowering = richer. Or, in other words if I have it right, screwing it down is leaner and unscrewing = richer.
 
Keoke,
AFAIK the Healey HS4 does have a jet adjusting nut.

GS,
Quote:
if I have it right, screwing it down is leaner and unscrewing = richer.
----------------------------
Must be a terminology problem. If you mean by screwing it down in which the nut assumes a higher vertical position & by unscrewing it causes the nut to move down vertically, you are correct. Higher nut, closer to you unless you are working from under the car, = leaner. In my mind? screwing it down moves the nut lower in the vertical plane, hence the use of CW & CCW as viewed from the top. /ubbthreads/images/graemlins/wink.gif
 
Oh My Gosh Yes! all them Hs thingies do.- /ubbthreads/images/graemlins/cheers.gif---Keoke
 
As my DFad always used to say.....

Lefty Loosey Righty Tighty for screws.

I think he knew.... Was a Tool and Die Maker.
 
I gave up following this thread when it went 'round before -- was afraid I would end up confused.

AFAIK -- for SU and ZS carbs -- leaning over the carb, looking down at the dome and visualing that nut at the bottom of the jet:

Left = Lean
Right = Rich
 
The jet adjusting nut threads into the carb body. If you are threading it in , you are leaning the mixture. Threading it out richens the mixture.
Jeff
 
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