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Discussion Starter · #1 ·
Call me what you will but i don't know where this thing is...I installed my White Bros R4 pipe and put the 165 main jet in...but that was the only change i made to the carb...i've read on here about guys turning them out and using washers..what does this do exactly...i'll tell you everything i have done so you'll know where i am and can point me in the right direction...i have a NOSS adapter and K&N filter with outerware...i plan on purchasing an outerware airbox lid from EHS racing so i can run with the lid off with no worries...the only other performance mod i have is the pipe....so where is this screw and how much should i turn it and what will washers do? feel pretty dumb...but i know i'll feel better when my beast is running perfectly...thanks

wesley
 

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It's right in the front of the carb, on the bottom, probably covered by a little rubber cap. If you have a CA model, it's covered by a brass screw that needs to be drilled out.

If you had the carb tipped to replace the main, you should have been able to find it. Alba's jetting page has a pretty good pic of it..

Look here:
http://www.albaaction.com/service/z400pipe.htm

In Figure 3, that's the carb. The brass screw thing on the very bottom of the pic is the screw. NOT the one above it that is flat... This pic is with the rubber (or brass if CA model) plug removed.

So, look at the bottom of the pic.. from left to right, big black hole, brass screw (that's it!) little black hole
 

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Discussion Starter · #3 ·
ok now i know where it is...what the heck does it do? should i play with it with my setup i guess is what i really need to know and do i need to shim with washers....thanks man...pic really helped...

wesley
 

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If you don't know what it's for, don't touch it. :) No, you don't shim the air/fuel screw with washers. Some do that with the needle jet.

If it's running fine and not overheating or making glow in the dark headers, leave it be.
 

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Discussion Starter · #5 ·
Ok i realize i'm not the smartest person in the world but i know i don't have to shim the air screw with washers..i know that if i shim it's the needle...i was only wondering what shimming the needle and adjusting the air screw would do? i'm assuming it controls the amount or air coming in to mix with the fuel...i am here to learn as much as i can about my quad...that's all i ask...thanks

wesley
 

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Sorry about that. The way you worded it sounded like somehow you wanted to shim the air/fuel screw. :) My bad.

The air fuel screw affects the low end. It's like a fine-tuner for the pilot jet, which controls the AF mixture from zero to about 1/8th-1/4 throttle. From there the needle takes over to about 3/4 to top end where the main jet takes over.

I'd do a search on google for carburator basics. There are a lot of good web pages out there that explain how everthing works together.

To answer your other questions, turning the air/fuel screw counterclockwise will richen the low end mixture, clockwise will lean it out. Past about 3.5 turns (from furthest in postition) it doesn't really affect any more.

Some carbs the screw does the opposite. Normally, though, if the screw is on the "engine side" of the carb, its like the Z (out=richer), but if it's on the "airbox side" of the carb, it's the opposite (out=leaner).

Shimming the needle will raise it, cause the AF mixture there to be a little richer.

These mods really aren't necessary unless you allow more air in (air box mod) and/or put on a new pipe (letting more air out). Remember, an engine is nothing more than a glorified air pump. :)

There's a lot more to it, but this should get you started. Again, searching google will really help a lot. You can REALLY get complicated with carbs and start messing with a lot more (like slides), but these basic things are all most anyone needs to fiddle with.

If you do plan on modding, I would suggest getting an aftermarket needle that allows you to change settings by moving the clip position (alba sells them seperatley, or they do come in jet kits, which IMHO are a waste of money).

The stock needle doesn't have these slots, which is why shims work. Tuners also use shims on needles with clips to fine tune even more (for example, if you want it a 3.5 from the top, put it on the 3rd clip with one shim washer). Again, that's getting more precise that most need as well.
 

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Discussion Starter · #7 ·
well i couldn't have asked for much of a better answer than that...thanks a lot man...there's a lot there i can use...i changed my main jet to a 165 when i put my new pipe on and my new filter adapter and filter...i ordered a new airbox cover from EHS racing also..it should be here early next week probably...maybe by this weekend...i ride in too much messy stuff and with a group of guys too much to run without a lid at all...i saw on alba's web page where they sold a jet kit and i even called them and asked them about it...i guess i'll call back and get one so i can get a needle that i can adjust...i read on alba's page that they turn their screw out three turns...and they run the same main jet i do...guess i'll start there and see what happens...thanks for your help...i needed it...later

wesley
 
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