Carb Jetting - ZX6R Forum
 
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post #1 of 1 Old 06-27-2007, 02:44 PM Thread Starter
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Join Date: Jun 2007
Location: goole
Posts: 66

I Ride: 1985 gsxr 1999 bandit 1200 zx6r
Carb Jetting

CARB JETTING :----

If you dont see it mentioned below it means its stock, so if you see Aftermarket muffler that means the airbox, filter, header, etc... is all stock.

These are all good starting points and I will get into tunning below these general starting points.


Aftermarket Muffler - Your bike already runs a little lean for emmissions and changing the muffler will cause it to run slightly more lean @ high rpm full throttle. However this alone does not qualify you for a jet kit and will not effect driveability at all.

Aftermarket Muffler & Header Restricted style or muffler with baffles - Same applies as above.

Aftermarket Muffler & Header Unrestricted stright through setup with a high free flowing muffler such as V&H & D&D - Now its true that you will find that your idle will most likely be a little eratic or funny. When I say funny I mean it will idle low but if you turn up the idle speed adjustment screw your idle will be too high, you just cant seem to find a nice idle @ say 1k. Sometimes your rpms will hang up as well, if they hang up badly this could be from an air leak as well or from the vent tube going into the valve cover being clogged which will usally cause oil to come out so you would know if that was the case. To fix this problem you can simply adjust the fuel mixture screws located @ the bottom of the carbs. At this time I would also install 1 step up in main jets. This would be a size 116 on a pre 98 750 and a size 108 on a pre 98 600.

Stock Exhaust & K&N Filter in Stock Housing - This is a tough one. I have never done this so I cant really comment on how much it would effect the bike. I would assume very very little. If anything I would say if the idle is the same as mentioned above then follow those directions completely including the main jet step up.

Aftermarket header with stock Muffler or muffler with baffles & K&N Filter - Same As Above

Aftermarket Header with Free Flowing Straight Through design Muffler and K&N Filter in stock air box - Ok Now you definetly need a jet kit. You will need to go with a full stage 1 kit including changing the mixture screw adjustment, dynojet needles, and main jets. At this point I would go with the 120 main jets on the pre 98 750 and 110 on the pre 98 600. If you feel like you need more then go one more step up BUT FIRST READ THE REST OF THIS POST TO FIND OUT WHERE YOU NEED IT.

Aftermarket Header with Free Flowing Straight Through design Muffler and K&N individual Filter pods - O Buddy now where talking. Your not making it around the block without a jet kit. So most people will say "hey with all that done go stage 3 140 mains or even better yet 144, yeah go big or go home" God I wanna slap people like that. Those people have probably never installed a jet kit, dont know what a jet kit looks like, how a carburetor works, and have probably never even changed their own plugs. Just agree and change the subject.
So at this point we only got up to using 120 mains on the 750 and 110 on the 600, do you honestly think were gonna jump into 140's ? no, no were not. were gonna focus on stage 2, for a 750 thats 126 & 130 mains for a 600 thats 116 & 120's.
Go ahead and throw in the 130's on the pre 98 750 and for the 600 go with the bigger 120's.
For the 600 you will place the E-clip in groove #3. For the 750 you will place the E-clip in groove #4 from the top.

So whats the stage 3 for ?

Aftermarket header with Free Flowing Exhaust & K&N filter pods with a PORTED HEAD or GSXR HEAD - Ok now you can use the 140 & 144 Mains on the 750 and the 130 & 134 Mains on the 600.



Tuning
Still not quite right ? Lets go ahead and break the carb into sections so you can undertand why we change what depending on what, did that make sense ?

Idle & a lil more is controlled by the mixture screw
up to 1/8 is controlled by the pilot jet
1/8 - 1/4 is controlled by the throttle valve cutaway
1/4 - 3/4 is controlled by the needle position
3/4 - full is controlled by the main jet

The throttle valve cutaway is the butter fly valve position in proportion to the size of the carb. i.e. 36mm etc...

Heres a diagram of what I think is a kehien Cv which is pretty much the same story


Ok I will go through them where I can tell what the shiate is pointing to

1- Vacuum Diaphram spring (controls the height that your slides can raise at which alters mid rpm / mid throttle performance
2- vacuum diaphram and slide
3- no clue what its pointing @
4- air hole that allows the slide to life (making this bigger will cause the spring to lift faster and visa versa)
5- maybe its pointing @ the needle, cant tell bit the needle and the height of the needle is important so lets leave it in here. (the needle height effects mid rpm/ mid throttle performance).
6- fuel, not important right now
7- Main jet (this determins your full throttle / high rpm performance, it is also tied into the needle which effects your mid rpm performance but im trying to keep this simple).
8- Pilot jet, dont worry about this right now
9- Mixture adjusting screws ( for now we will say idle and low rpm)
10- Throttle valve butterfly (this is what your throttle cables opens and what ultimatly controls the overall air flow into the motor).

So from that you should be able to pin point your problem if you have one and where to start. If not Ill help a little.

Idle sucks - try mixtures screws, look for air leaks of any type including around the boots that connect the carbs to the motor and the carbs to the airbox. Also if you have aftermarket filter pods DO NOT PLUG the valve cover breather like you do on some other bikes. Check for flooding due to bad float needles or incorrect float hieghts.

Mid Rpm Trouble - this usally kicks in around 2k-3k. Does she bog down a lil or fall flat on her face. Falling flat on her face and the engine changine tone drastically with alot of engine noise is usally a lean sign. This is in the needles, make sure your mixture screws are 2.5 turns out or whatever dynojet says for a stage 1 kit (if your all stock why are you reading this?) and raise the needles 1 notch by dropping the e-clip down 1 notch to fatten up the mixture.
Remember you cant hurt a motor by going to rich.

High rpm / full throttle trouble - Ok now you can finally point @ the mian jets. No matter what it seems like always go richer first, if it gets worse then go leaner.

I cant yet comment on the slide hole correctors because I got the wrong needles in my jet kit and this is the first bike that I have seen that uses them.
Personally I am only going to use 1 start off with because the correctors reduce the orifice opening and will slow down the speed @ which the slide can lift which will inturn cause the bike to be more lean going up through the mid range when you really bang on the throttle hard. I will dyno the bike and see if im right once its in.

Ok now that your damn damn close its a good idea to get a carb sync when you can and also get to the dyno for that ultra fine tunning.
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