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Carb adjustment query

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Kwackman
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Carb adjustment query

#1 PostAuthor: Kwackman » Thu Jan 10, 2019 5:55 pm

Hi,
I've been restoring a little Z400J over the last 2 years.
Last week it was started for the first time and it won't run under 3500-4000 RPM.
Removed the carbs (rebuilt a few months ago) and checked the pilot jet was clean (it was, it's new) and was the correct size. I checked the air screw on the side of each carb.
So, I looked at the manual and the slides don't seem to be at the correct height when the throttle is closed.
The method for adjusting is attached. The diagram B22 (top right) is my problem. I don't know if this is to be measured looking from the carb's inlet, or outlet port, as the heights are different? Does anyone know? Thanks in advance.
Carb set up.png
Carb set up.png (268.89 KiB) Viewed 557 times
2006 ZRX1200R
1982 Z400J project

ex owner of Z1100R
GXI 2752 are you out there?

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chrisNI
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Re: Carb adjustment query

#2 PostAuthor: chrisNI » Thu Jan 10, 2019 6:03 pm

It’s at the back you can’t measure at the front because of the throttle valve cutaway. But if it’s not running under 3500 it’s likely still a pilot problem, you can clear the jets (or replace) a lot more easily than clearing the little jet passages they can be a right b******* chances are they’re still clogged up in there.

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Kwackman
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Re: Carb adjustment query

#3 PostAuthor: Kwackman » Thu Jan 10, 2019 7:11 pm

Ta for the reply Chris.
"back" means the airbox side?
The pilot jets are new, I've blasted the airgun up them now.

It's my first carb rebuild, so no doubt I've done something stupid!
2006 ZRX1200R
1982 Z400J project

ex owner of Z1100R
GXI 2752 are you out there?

Philippe
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Re: Carb adjustment query

#4 PostAuthor: Philippe » Thu Jan 10, 2019 8:54 pm

Hi Kwackman
you put a wire in the carb at the side where they go into the intake rubbers. Just take a look at the throttle valves,(slides) there's a small indentation. The wire has to sit in that indentation, trapped between the carb body and the slide.
Hold your carbs with the outlet side downwards and turn the adjusting screws in. By doing that the valve will lift and the wire will fall out.
Do it with the four carbs and check it, if they're not equally lifted, repeat until they're equal.
Practice makes perfect!!!!
GrtZ
Philippe
the differences between a little boy and an adult man is the price and size of their toys!

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zed1015
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Re: Carb adjustment query

#5 PostAuthor: zed1015 » Thu Jan 10, 2019 9:35 pm

You use the wire method on the lowest part of the slide which is closest to the engine (opposite the airbox) but it is only to get all the slides at the same height in relation to each other for initial set up or bench syncing.
Once done the idle should be adjusted on the idle screw and at this point the slides would be barely off their seats.
Also once balanced correctly using vacuum gauges the slides almost never end up all at the same height ( except maybe on a brand new fresh built motor ) as each cylinder won't be producing exactly the same power at the same throttle opening so once balanced they will end up being slightly different heights to each other.
If the engine cuts out below 3/4000k revs you may still have blocked or partialy blocked passages in the pilot circuit even though the actual jets are new and clean.

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Kwackman
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Re: Carb adjustment query

#6 PostAuthor: Kwackman » Thu Jan 10, 2019 9:52 pm

Thank you both for the replies.
Thanks for clearing up the initial set-up process.
But, as you and Chris (and others) reckon it's the pilots that are the problem, I'm going to re-check that end of things.

Thanks again for the advice, much appreciated.
I'll let you know how it goes.
Davy
2006 ZRX1200R
1982 Z400J project

ex owner of Z1100R
GXI 2752 are you out there?

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chrisNI
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Re: Carb adjustment query

#7 PostAuthor: chrisNI » Thu Jan 10, 2019 10:19 pm

Kwackman wrote:Ta for the reply Chris.
"back" means the airbox side?



Sorry for not being clear I meant front being where the air goes in and back where it goes out. As others were clearer about.. :shock:

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Kwackman
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Re: Carb adjustment query

#8 PostAuthor: Kwackman » Thu Jan 10, 2019 10:24 pm

No problem Chris, thanks anyway.
As you & others have pointed me back to the pilot part of the system, I'm now accepting this is where my problems lie!
2006 ZRX1200R
1982 Z400J project

ex owner of Z1100R
GXI 2752 are you out there?

User avatar
Kwackman
100Club
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Posts: 180
Joined: 13th Nov 2009
Location: Belfast

Re: Carb adjustment query

#9 PostAuthor: Kwackman » Fri Jan 11, 2019 8:26 pm

Still a bit stuck, so returning for more help/ideas!
I did this initial wire method, measuring fro the side nearest the engine.
I got the gaps to be all the same, around .75mm.
That page I showed in my first post shows the locknut to tighten.
The problem is that the screw isn't in far enough for the lock nut to catch on the top of the body.
Here's pictures of where my adjustment screw has ended up (for the nut to lock those the thicker thread needs to be lower?), and photos of the screw and locknut & washer to explain better than I can type.
Currently, if I open the throttle, all slides clear the top of the bore by a small margin, and all seem about the same height.
Can't figure out what I've done wrong. I don't THINK I've assembled that linkage wrong, there's not much I could have messed up...?!
Adjust 1.jpg
Screw lock1.jpg
Scrw lock 2.jpg
Gap.jpg
2006 ZRX1200R
1982 Z400J project

ex owner of Z1100R
GXI 2752 are you out there?

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zed1015
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Re: Carb adjustment query

#10 PostAuthor: zed1015 » Fri Jan 11, 2019 8:43 pm

You need to start with the adjuster screws turned a few more threads in so that the top of the larger thread is below the surface before you start and then level the slides with the wire method and make sure you only turn the screws clockwise from their initial position.
That way the nut and washer will be able to lock on the top of the throttle arm .
Use the idle screw on the cable reel to lift the slide bank up far enough to allow the slides to hang in their bores so you can do this.
The slides will still lift clear of the venturi at full throttle.
Last edited by zed1015 on Fri Jan 11, 2019 8:51 pm, edited 1 time in total.

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Kwackman
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Re: Carb adjustment query

#11 PostAuthor: Kwackman » Fri Jan 11, 2019 8:47 pm

zed1015 wrote:You need to start with the adjuster screws turned a few more threads in so that the top of the larger thread is just below the surface and then level the slides with the wire method and make sure you only turn the screws clockwise.


Ta for the reply Zed1015.
If I start with the adjuster screws turned in so the lock nuts can do their work, the gap decreases and the wire won't fit in. The adjuster screws control the gap.
2006 ZRX1200R
1982 Z400J project

ex owner of Z1100R
GXI 2752 are you out there?

User avatar
zed1015
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Re: Carb adjustment query

#12 PostAuthor: zed1015 » Fri Jan 11, 2019 8:54 pm

Kwackman wrote:
Ta for the reply Zed1015.
If I start with the adjuster screws turned in so the lock nuts can do their work, the gap decreases and the wire won't fit in. The adjuster screws control the gap.


No! The adjuster screws only adjust the slides in relation to each other.
It is the idle screw that runs on the cable reel that the controls the gap ( slide heights )
You are starting with the slides too low in their bores with the idle screw backed off that far that it isn't lifting the slides first.
Use the idle screw to lift the slides enough so that you can drop the slides back down on their adjusters to get the required gap and also the nuts to lock on top of the arms.
Last edited by zed1015 on Fri Jan 11, 2019 9:05 pm, edited 1 time in total.

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Kwackman
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Re: Carb adjustment query

#13 PostAuthor: Kwackman » Fri Jan 11, 2019 9:04 pm

Ah ZED1015, I think you've just solved my problem, and I'll sleep better tonight!! :D

So, the manual page I put in the first post, just under the diagram B21, when it says
"Turn the adjusting screw to make a slight clearance
between the throttle valve and the bottom of the bore"
it means the IDLE ADJUSTING SCREW not the THROTTLE ADJUSTING SCREW?
2006 ZRX1200R
1982 Z400J project

ex owner of Z1100R
GXI 2752 are you out there?

User avatar
zed1015
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Re: Carb adjustment query

#14 PostAuthor: zed1015 » Fri Jan 11, 2019 9:15 pm

Kwackman wrote:Ah ZED1015, I think you've just solved my problem, and I'll sleep better tonight!! :D

So, the manual page I put in the first post, just under the diagram B21, when it says
"Turn the adjusting screw to make a slight clearance
between the throttle valve and the bottom of the bore"
it means the IDLE ADJUSTING SCREW not the THROTTLE ADJUSTING SCREW?


YES! The text under image B21 is slightly confusing and unclear as it doesn't differentiate which adjusting screw is which.
The first mention is for the Idle screw and the second for the Throttle slides.

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Kwackman
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Re: Carb adjustment query

#15 PostAuthor: Kwackman » Fri Jan 11, 2019 9:19 pm

BRILLIANT!
Thanks Rob (I finally remember your name!), I really appreciate your help- I was getting very lost!
That's another pint I owe you.

Now I can concentrate on the pilot system...
2006 ZRX1200R
1982 Z400J project

ex owner of Z1100R
GXI 2752 are you out there?


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