Ratters
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| posted on 13/1/09 at 09:53 PM |
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bike carb a/f ratio/jetting
i currently have zx9r carbs on a 1700 x-flow. at a recent rolling road dyno day i managed to get a air/fuel ratio print out which shows the engine
running rich at low end & top end & leaner in the mids.
is this going to be easy to sort out or not?? i'm guessing the main jets are going to effect the top end?? they are 140's in there.
thanks
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Ratters
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| posted on 13/1/09 at 09:59 PM |
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here's the graph. it's the line with the dots - showing the peek at 40mph.
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Dingz
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| posted on 13/1/09 at 10:08 PM |
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I think you will need to change the needles, like used to be done on SUs, they had loads of different tapers to sort this, I assume mikuni etc. make a
range but suspect it will be a long and expensive job to sort 
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BenB
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| posted on 13/1/09 at 10:16 PM |
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is the typical bike carb graph....
It's a good place to start looking for answers. Bear in mind carbs are always going to be a compromise...
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Ratters
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| posted on 13/1/09 at 10:21 PM |
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thanks guys.
it was a full throttle 3rd gear power run - yes the gearing is low  i'm estimating the graph shows from 2,250 to about 6,000 rpm so i'm
guessing a smaller main jet??
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Nick Skidmore
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| posted on 14/1/09 at 09:26 AM |
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I would say,
Adjust air screw / change jet to lean it off a little.
LIFT the needle ie lower the circlip to its bottom or next from bottom position.
Top end looks about right for power but you could try a leaner main to see what happens.
The jets are available from most decent bike shops as mikuni jets will fit most of the carbs in the range.
Needles are quite adjustable but if you need to change them buy the dyno-jet kit as the most cost effective option.
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NOTE:This user is registered as a LocostBuilders trader and may offer commercial services to other users
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Ratters
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| posted on 14/1/09 at 05:26 PM |
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thanks nick
i don;t know a lot about the carbs tbh. i don't think the needles are adjustable with the circlips - will have to take a look though.
how much is the dynojet kits?
this is where i'm torn between getting these set up properly or swapping to 45's which a lot of tuners can easily deal with - i'm
estimateing a 45's swap brand new all in to cost best part of a grand though 
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Ahdammit
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| posted on 14/1/09 at 08:44 PM |
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If the needles dont have circlip grooves,you can raise them with little washers.
I got some in a model aeroplane shop.
Like Nick says,I'd try a smaller main.
Bike carbs are usually set up in the order-
Main jet
needle
idle jet/mixture
ie-set up the main jet first as any changes you make to that will also affect needle jetting as well.
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Ratters
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| posted on 14/1/09 at 10:30 PM |
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thanks again for your advice 
if it's running 140 minas now [i'm 99% sure it's 140's] what do you reckon to drop down to?? i know i can swap them ok.
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Ahdammit
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| posted on 15/1/09 at 11:49 PM |
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It's impossible to say,could be 135,130,etc.You really need to set it up properly or use a lambda guage if you can get hold of one.
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Ratters
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| posted on 17/1/09 at 04:20 PM |
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cheers. the trouble is i'm struggling to find someone who is interested in setting them up & who has jets for them....
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jacko
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| posted on 17/1/09 at 06:29 PM |
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quote:
Originally posted by Ratters
cheers. the trouble is i'm struggling to find someone who is interested in setting them up & who has jets for them....
Where do you live?
What model zx9r carbs do you have ie c/ b/ e some carbs have different size jets in the 4 carbs ie 165 out side 160 in the middle 2 carbs
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Ratters
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| posted on 18/1/09 at 11:52 AM |
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i live in bristol. not sure what model they are but here's some pics of when i first had them. i know they have all got 140 mains in them, i
remember checking a long time ago.
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jacko
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| posted on 18/1/09 at 09:09 PM |
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In your first photo there is some holes in line with the main needles [ brass] try blocking them with some alloy welding wire then try a ride in the
car [ this is what Bogg Brothers did to mine]
make sure you can pull them out if it dose not work
Jacko
[Edited on 18/1/09 by jacko]
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jacko
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| posted on 18/1/09 at 09:13 PM |
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Have a read of this post
quote:
http://www.locostbuilders.co.uk/viewthread.php?tid=104526&page=&contribmessage=none
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