cooler weather and air screw position

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#1
As weather continues to get cooler and hopefully less humid, how does this effect carborator richness,jetting and air screw position?

Thanks for your responses.
 

Braahp

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#2
The air will have more oxygen in it (your mixture will become leaner) so adjust carb slightly richer if it needs it.
 

CaptainObvious

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#3
As braahp mentioned, to compensate for the greater O2 content of colder air you'll need to richen the mixture. The pilot circuit can be adjusted with the air screw (assuming that it isn't turned beyond 3/4 in right now). Depending on how cold it gets by you and how long into the winter you ride, you will want to go with a richer main jet, one to two sizes. You will likely need to drop the clip on the needle too.
 
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#4
This might be a dumb question, but...

Is it considered a "rule of thumb" that your airscrew shouldn't be turned in beyond 3/4 of a turn. Just curious because that is where I am at the moment.
 
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#5
My 89 200 runs the best at a ½ turn out????? I’m running 1173 needle 3rd clip and a 52 pilot up from the 48. It’s has been ported (FRP) piped and has a rad valve. I’m on my 2nd carb the first one just wore out, but it was the same ½ turn out other wise it runs and starts great. I just had the cylinder re-plated too. I've had it since 1991 and it's always been that way,hot or cold.
 

CaptainObvious

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#6
seancza, the air screw should be between 3/4 to 2 turns out. More than 2 turns indicates that your need a smaller pilot jet, less tha 3/4 means you need a larger pilot jet.

kx200, The air screw doesn't affect the needle - they are different circuits. Overlap of the pilot jet and needle occurs at 1/8 throttle where the air screw has no effect. A 52 pilot jet and clip in the 3rd position with an R1173N needle? There must be a lot more O2 where you live! That is by far the richest pilot I have heard anyone using in a KDX with the stock PWK carb.
 

tedkxkdx

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#7
I am at sea level or slightly below and I run a 45 pilot for less bog and retain my 160 main year round. I could probably go bigger than 160 even. I did not need to do plug chops because I could feel the bike pulling better in the wheat field I tested in. The lower mains made me top out and not allow over rev. Remember FRP ported and 211cc engine. I think some people are sitting nearer sea level and are jetting for higher altitudes. Just seems that from reading posts. A table broken out by altitude would be good.
 
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#8
All of you RB folks....remember that your pilot circuit has been modified. It is much more effective as a tuning device. Teeny-weeny air screw changes will make HUGE differences in the way your bike runs.

If you don't know where your air screw is and why it's there......it's in the wrong place!
 

Jim Crenca

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#9
CC,

Airscrew sensitivity may not be as great on older carbs says Ron.
Also, as with any R&D project I think that R&B may do mods differently now than from a few years ago due to feedback from guys like us.
 

Jim Crenca

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#11
Ron tells me that you have to change carbs as you've had the thing apart so many times that the original threads wore out, and, you can only heli-coil that junk alloy a few times. :thumb: