Pilot adjuster screws, final verdict

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Pilot adjuster screws, final verdict

Post by banner001 » Tue Apr 15, 2014 10:50 am

Dont want to start an argument, i want this to be a rational debate.

As part of the general cleanup of the site i want to lay this confusion to bed as i will be making a general fuelling FAQ in the near future.

I have always been led to believe that the CVK-D32 carbs have a fuel mixture screw, every pair of carbs that i have seen that have a screw in the same place is a mixture screw. When i took the bike to Jordans Dyno in Leeds they told me it was a mixture screw, James Brennan a former racer who owns the DIY garage in coventry has told me that its a mixture screw, and today i recieved this from Kawasaki UK:-

"Dear John,

Thank you for contacting Kawasaki Motors UK.

There is no specific mention in the workshop manual regarding if the pilot screw adjusts the air or fuel amounts, however as a general rule, if the pilot screw is located near the engine side of the carburettor then it adjusts the amount of fuel ie screw it out adds more fuel (richens mixture), screw it in reduces fuel amount (leans mixture). If the pilot screw is located near the air box side of the carburettor then it adjusts the amount or air ie screw it out adds more air (leans mixture), screw it in reduces air amount (richens mixture).

Looking at the workshop manual the pilot screws are located engine side of the carburettor, so screwing the pilots screw in would make the bike run leaner. The standard pilot screw setting is 1 and a half turns out.

I hope this information is of assistance to you.

Kind Regards,

Matthew Callaway
Technical & Customer Services Group

Kawasaki Motors UK
1 Dukes Meadow | Millboard Road | Bourne End | SL8 5XF
T +44 (0)1682 856750 | F +44 (0)1628 856798
customerservice@kawasaki.co.uk | http://www.kawasaki.co.uk"

After replacing my head gasket i tinkered with my bike, screwing the pilot adjusters clockwise inwards until they seated i backed them off to 1 turn out, the bike required some choke to start (i.e. its lean), after screwing them out to 2.5 turns out the bike didnt require choke (i.e. mixture was good to possibly rich).

Other than the online kawasaki parts diagram stating "Screw - Pilot Air", no other place refers to it as an Air screw, we have all come across inaccuracies in manuals before, i believe that this is innacurate as the workshop manual just refers to is a "Pilot Screw". And if Kawasaki UK and a respected Dynojet Operator say its a mixture screw, then until other evidence comes to light we will be calling it a mixture screw - any by evidence i mean a dyno trace before/after touching only the mixture screw.

To repeat: Until other information comes to light, you screw the pilot adjusters OUT for richer, and IN for leaner.

I have sent an email back to Kawasaki UK:
"Thank you Matthew, just for my own piece of mind, are there any carbs fitted to kawasaki motorcycles that have an air mixture screw located on the engine side of the carb? Its just that the http://www.kawasakioriginalparts.com/ website lists the UK zxr 400 L4 pilot screw as "screw - pilot air" which makes it seem like it regulates air as opposed to mixture...i think this is where my confusion is coming from. Any information you could shed on this would be greatly appreciated.

Thank you

John"

Also, for the record, im a scientist, i dont mind being wrong, but where i see 2 competing theories i would like the issue of which one is correct to be resolved, and resolved with evidence as opposed to "i said so". If you wish to discuss this in a reasonable manner please reply below.
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Re: Pilot adjuster screws, final verdict

Post by ross46 » Tue Apr 15, 2014 9:28 pm

well after tinkering with my bike earlier as the exhaust had come loose (no springs holding it together so really need to find out what make it is) so i fixed that and changed the mixture screws. i was in a rush and now my bike is stranded a mile away from my house running WAAAY too rich, its currently on 1 3/4 turns out so will change it and see which way it needs to be turned. i personally always thought it was out for richer and in for leaner, but i may be wrong. experiment time! after my mile walk with a car battery to jump it that is.

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Re: Pilot adjuster screws, final verdict

Post by banner001 » Wed Apr 16, 2014 2:07 pm

A follow up:

"Dear John,

I believe the 'screw - pilot air' is a generic term for the pilot screw as it does adjust the fuel/air ratio wherever the screw is located on the carburettor. Depending on the carburettor manufacturer and its design, the pilot screw could be located either side. I am not aware of a pilot screw which is located on the engine side which leans the mixture when you screw it out fitted to our bikes.

Kind Regards,

Matthew Callaway"
UK ZXR400 L3 (1993) - Fully restored and on the roads, my green beast!
JPN ZXR250 A2 (1990) - Revs to 19,200rpm... 'nuff said :smt003

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Re: Pilot adjuster screws, final verdict

Post by banner001 » Thu Apr 17, 2014 3:38 pm

if i get the chance this weekend, im going to do a little experiment with the carbs, measuring where the air and fuel are going.

rmkd, jimsym, deswilke as you have been so fervent in your opinions i especially would like your input into this.

we have 2 theory's:-
1. air goes into the pilot air corrector jet at the top of the carb near the airbox and gets metered by the pilot screw, this jet of air then goes past the pilot fuel jet, picks up fuel and then deposits it out of the single hole underneath the butterfly close to the engine.

2. air goes into the pilot air corrector jet at the top of the carb near the airbox and goes past the pilot fuel jet, picks up fuel and gets metered by the pilot screw, and is deposited out of the single hole underneath the butterfly close to the engine.

if these ideas are correct (if not please tell me where i am going wrong) there is an easy way to test where the air is going.

I will screw in the pilot (air) screw until it seats and blow air down the pilot air corrector. if theory 1 is correct then the air wont go anywhere, as the air screw has blocked the passage of air fully, if theory 2 is correct then the air will be blocked from coming out of the hole under the butterfly...but it will come out of the pilot fuel jet in the fuel bowl.

This should tell us how the pilot air corrector and pilot fuel jet are connected, and if the flow of air between them requires the screw. If the pilot screw has an effect (i.e. air goes nowhere) then it is acting as a pilot air screw, it is metering the flow of air into the pilot system of the carb. If the pilot screw when fully seated causes air to only come out of the pilot fuel jet in the float bowl then we must conclude that the pilot air corrector and pilot fuel jet are connected by a pipe that doesnt get altered by the pilot screw, in this instance the pilot screw is varying the amount of fuel/air mixture that enters the carb.

Is this setup ok, before i start does anyone have any objections, changes to my methodology, or interpretation of results?

Just to be clear, if theory 1 is correct, the pilot screw when fully seated will block air from going down the pilot air corrector jet entirely. Therefore screwing the pilot screw inwards will reduce the flow of air (richer) and screwing it out will increase the flow of air (leaner).

If theory 2 is correct, the pilot screw when fully seated will block air from entering the carb underneath the butterfly, but will cause air to emerge out of the pilot fuel jet in the float bowl. This indicates that the pilot air corrector jet and pilot fuel jet are physically connected to each other irregardless of the setting of the pilot screw. In this case the screw controls the volume of the fuel/air mixture, screwing it in restricts this volume (leaner) and screwing it out increases this volume (richer).
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JPN ZXR250 A2 (1990) - Revs to 19,200rpm... 'nuff said :smt003

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Re: Pilot adjuster screws, final verdict

Post by ross46 » Mon Apr 21, 2014 6:53 pm

i like the scientific method. only thing i can see wrong and i may be incorrect but is if you screw the pilot screw all the way in then the bike still runs but exhibiting lean symptoms ( to get mine to start i screwed it all the way in, it ran but with the idle very high no matter what i did with the idle adjuster) so it wont completely block the passage, though if the butterflies are open slightly then it will let fuel through out of the main jet holder. i may be wrong and will be happy to admit if their is evidence to prove otherwise. on the original note as stated above i screwed the pilot screw all the way in and it seemed to lean out the mixture as it then exhibited lean symptoms but without a probe to measure exhaust gases this can not be proven categorically as it is a qualitative test rather than quantitative which is what is needed to settle this dispute once and for all. so if any of you guys are going to a dyno it would be greatly appreciated if you could screw the pilot screw all the way in and give us the two graphs with the fuel trace on it.

edit- i have just contacted k&n on this subject as they supply a jet kit for this bike and advise on the settings so they should be able to give the answer as it is what their business replies on

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Re: Pilot adjuster screws, final verdict

Post by banner001 » Tue Apr 22, 2014 8:36 am

ross46 wrote:i like the scientific method. only thing i can see wrong and i may be incorrect but is if you screw the pilot screw all the way in then the bike still runs but exhibiting lean symptoms ( to get mine to start i screwed it all the way in, it ran but with the idle very high no matter what i did with the idle adjuster) so it wont completely block the passage, though if the butterflies are open slightly then it will let fuel through out of the main jet holder.
the coaster enrichers are always open (thats the 5 small holes where the butterfly meets the inside of the carb) and are not metered by anything other than the pressure in the venturi, so these will always be drawing a small amount of fuel through.

didnt manage to get my carbs off this weekend, entertaining 2 guests one of whom gave me a wonderfull cold on sunday...but the face that yours appeared lean when you screwed it in is a +1 for method #2, ill be interested to hear what k&n have to say, i think i still have my booklet from the dynojet kit, ill check what it says in there too.
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Re: Pilot adjuster screws, final verdict

Post by ross46 » Tue Apr 22, 2014 2:18 pm

i had completely forgotten about the coaster enrichers, i will let you know what k&n say. and their leaflet that comes in the kit is on this post

http://zxrworld.co.uk/zxr400oc/viewtopi ... 75#p112553

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Re: Pilot adjuster screws, final verdict

Post by ross46 » Wed Apr 23, 2014 8:53 pm

From K&N tech support...

"The mixture screw is a fuel screw, the more you turn it out it richens up the idle and when you turn it in it leans it out.

Let me know if I can be of any further assistance.

Thank You!"

also please see this website which is by Factory Pro which is a competitor of K&N

http://www.factorypro.com/tech/tech_tun ... gines.html

"If lean surging is encountered, richen mixture screws (turn out) in 1/2 turn increments"

so that is Kawasaki, K&N and Factory Pro that say YOU TURN THE PILOT SCREW OUT TO RICHEN THE IDLE MIXTURE

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Re: Pilot adjuster screws, final verdict

Post by banner001 » Thu Apr 24, 2014 6:04 pm

Had a nice PM from Deswilkie:
Banner, you are a total ballbag. Get a Fucking life.

See you in a week :smt006

Back to a rational discussion now...
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Re: Pilot adjuster screws, final verdict

Post by daftylad » Sat Apr 26, 2014 4:55 pm

Banner001, on the "mixture problems-advice needed" thread (see page 3) you wrote:

by banner001 » Tue Nov 27, 2012 3:13 pm
ross46 wrote:Right on my way home I tried using the choke, it killed the bike when at low revs so under 3-4k revs, 4-6 the power was similar but with more popping and banging, above 6 it felt more powerful with less banging but still quite flat, and at high revs it was alot better, so im guessing lean out low down, so screw in mixture screws, increase float height, and richen needles and main jets? Still think dynojet would be a good investment, have pm'd you Robbie but not sure if it went through properly, what are the symptoms of an air leak? And is the airbox supposed to have a seal?


"air mixture screws are screw out to lean, screw in to richen. you might benefit from setting them all to the same value, as yours are fairly high, set them all to 3 1/2 turns out and go from there. also if you are running full system, look at a different air filter, this will also help to lean out your pilot/idle if you think you need it. after you get everything sorted balance your carbs, then you can start to tune the carbs, before a final balance.

increasing float height will richen your system throughout.

the carb to airbox plate should have a fabric/foam seal between it and the airbox.

air leak will cause revs to hang and might cause the revs to hang around 2-3k rpm...although a similar condition can also be caused by weak vacuum springs...slipping the clutch usually brings the revs back down to 1200."


FFS, what a total contradiction!

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Re: Pilot adjuster screws, final verdict

Post by banner001 » Sat Apr 26, 2014 10:50 pm

Sorry. I forgot to add that on here it is illegal to change your views as new evidence comes to light.
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Re: Pilot adjuster screws, final verdict

Post by RedexRobB » Sun Apr 27, 2014 7:15 am

How unscientific! You should be ashamed of yourself banner!

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Re: Pilot adjuster screws, final verdict

Post by banner001 » Sun Apr 27, 2014 8:25 am

RedexRobB wrote:How unscientific! You should be ashamed of yourself banner!
I know. Its terrible isnt it. I go along with the untested status quo...test it, determine its possibly incorrect and change my viewpoint...what kind of scientist would i be if i didntstick to the facts, rely on only blind faith and shun any kind of reasoning.
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Re: Pilot adjuster screws, final verdict

Post by ross46 » Tue Apr 29, 2014 6:00 pm

you would be called a christian.. or any religion for that matter....

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Re: Pilot adjuster screws, final verdict

Post by CaNsA » Tue Apr 29, 2014 6:12 pm

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