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-   -   Z900 high & rising Idle issue 3-5K (http://www.biker.ie/forum/showthread.php?t=246564)

Airman 8th November 2018 10:50 PM

Z900 high & rising Idle issue 3-5K
 
She started !!:thumbsup2:
Then went up and up... to nearly 5K RPM on half choke.

New Plugs gapped
Valve clearances done.
Air screws out 1.5 std turns on each carb x 4
No leaks. (That I can see)
Float heights 99%
Throttle back set on butterfly
Correct slack on throttle cables.
Carb Sleeves set 0.6mm up from closed
Needle clip at mid position 3 of 5
Jets 2 years old ish - running fine.
The idle screw is backed out loose.

Started fine after a few turns after being apart for nearly a year. rough though.. so the plan was to do the timing. Boyer fitted.
At ~ 1000 its too erratic to see where the timing line is.
about a minute of running the revs rise to nearly 5 before I kill it.
but at this point the timing line is closer to TDC than F

Turned down the air by 0.5 turns
Still climbs way too high on its own to ~ 4K.
So.. I have it in my mind to lower the sleeves, which is a bit iffy as I can't gauge them then from having them set at 0.6 ish.
Any pointers welcome - major grey area for me

DavyH 8th November 2018 10:52 PM

Re: Z900 high & rising Idle issue 3-5K
 
Have to attempted to balance the carbs yet?

Airman 8th November 2018 11:00 PM

Re: Z900 high & rising Idle issue 3-5K
 
[quote=DavyH;3556983]Have to attempted to balance the carbs yet?[/quote]

That's the last step, even if I wanted to have a look, not in its current state.

the landshark 8th November 2018 11:15 PM

Re: Z900 high & rising Idle issue 3-5K
 
Try spraying wd40 aerosol around the carb boots. The butane propellant will make it rev up if it gets sucked in an air leak.
I had to make gaskets for mine to seal the boots to the head.

Airman 8th November 2018 11:45 PM

Re: Z900 high & rising Idle issue 3-5K
 
[quote=the landshark;3556985]Try spraying wd40 aerosol around the carb boots. The butane propellant will make it rev up if it gets sucked in an air leak.
I had to make gaskets for mine to seal the boots to the head.[/quote]

Was going to do that but got a dose of 'couldn't be arsed at this hour'.
However.. As I've been so meticulous in putting it back, all the rubbers are perfect, clamped squarely etc .. never say never, will give it a go tomorrow.
Just collecting ideas
I suppose a leak would make her erratic also ?

2wheelsrbetter 8th November 2018 11:57 PM

Re: Z900 high & rising Idle issue 3-5K
 
How did you set up the slides ? Did you use the 0.6 mm drill bit to set them up, sounds like they are too high .

Airman 9th November 2018 12:18 AM

Re: Z900 high & rising Idle issue 3-5K
 
[quote=2wheelsrbetter;3556989]How did you set up the slides ? Did you use the 0.6 mm drill bit to set them up, sounds like they are too high .[/quote]

Ya. 0.6 pin gauge, just pushed it in gently backing the slide off until it was just biting.
book says the 'notch' at the bottom of the slide is 0.4mm x 2mm wide where the 0.6 pin goes. Just checked mine and it's 0.2 x 2
Still I doubt 0.2 higher would bring the revs to 5K idle.
Pic here: [url]http://www.biker.ie/forum/showthread.php?t=241723&page=2[/url]
As mentioned - idle adjust screw isn't touching, slides are down as far as they are set.
Must be a leak, as the rpms race up
I'm confused... as it rises, it seems to run even but is erratic before it does at 1K

2wheelsrbetter 9th November 2018 12:49 AM

Re: Z900 high & rising Idle issue 3-5K
 
That sounds spot on , it must be an air leak causing it , sorry I'm no more help to you

dean_c 9th November 2018 08:45 AM

Re: Z900 high & rising Idle issue 3-5K
 
Really does sound like an air leak, Do your carbs have rubber choke seals?? Check them for leaks too......ask me how I know :doh:

crispy 9th November 2018 12:46 PM

Re: Z900 high & rising Idle issue 3-5K
 
[quote=Airman;3556981]She started !!:thumbsup2:
Then went up and up... to nearly 5K RPM on half choke.
[/quote]

I had a late 80's Kawasaki GT750 and seem to remember 4k (initially) was average on choke when cold.

H1500 9th November 2018 01:37 PM

Re: Z900 high & rising Idle issue 3-5K
 
If it is smooth ending outas the revs increase it is almost certainly and air leak. That is caused by the fact that at idle the leaking air is a higher proportion of the total mass of air and hence it runs lean. As the revs come up the proportion of air that comes from the leak is smaller and hence it richens up.

The reason it runs faster is related to the reduced vacuum downstream of the carb.

Spray around the carbs and inlets with a water mist bottle and you should be able to find it. It might be the carb tips rather than inlet rubbers or gaskets. You oould use other things like wd40 or brake cleaner but they will mess up your shiny newly refurbished engine and leave you with a cleaning job. Some guys use propane. It is very good on a bike with injection and an O2 sensor but I don't use it on bikes with carbs.

Hopefully this helps

ridelikeaturtle 9th November 2018 11:19 PM

Re: Z900 high & rising Idle issue 3-5K
 
Just another data point: perished rubbers around the carbs will wreak havoc, as did on an old ZXR400 I had years ago.

"Ether" or "starting fluid" will show up any leak very quickly, and shouldn't leave much (if any) residue.

Eliminate, or fix, that possibility first. Then you can get to balancing and tuning.

Airman 10th November 2018 12:12 AM

Re: Z900 high & rising Idle issue 3-5K
 
Thanks all.

big change in the running rpm
I milled a locating slot in the magnet disc of the timing plate, (Boyer say tap it with a hammer to make a dent where the lugs are and file them a bit).
This caused the disc to bolt in closer to the timing plate with the pickups than it was and was .1 away from the coils, backed it out about 4mm & ran a good bit better which is wierd.

Still shit though, so .. pulled the carbs out anyways.
No leak to be found.no perishing, still soft and all clamped OK.

No 3 was not pulling [U]any[/U] vacuum at all before I took them out.

No 2 rubber carb holder bolt had pulled the threads so wasn't super tight.
Longer bolt .. sorted, gave them all an extra squeeze.

No. 4 pilot jet was tight but over 1/2 way out.
when I put them together, I go across all four. Jets 1, 2, 3, 4, Pilots 1, 2, 3, 4 obviously I just turned until it stopped.

Can't see anything at all wrong with No 3, ... back in tomorrow... we'll see.
Thanks again for the direction.

Jack stowage 10th November 2018 11:48 AM

Re: Z900 high & rising Idle issue 3-5K
 
Are all the choke lifters in sinc..??..i mean are they all shutting off..are the balancing rubber caps tight...?

Airman 10th November 2018 09:41 PM

Re: Z900 high & rising Idle issue 3-5K
 
Sorted. Thanks :thumbsup2:
No leak to be found.
Pulled them apart and rebuilt them again.

1/4 turn in on 2 & 3 air.
1/2 turn in on slides 2,3 & 4
Shitty. Theres no linkage between the slides. They are all bolted to the main shaft so independent adjustment is via two bolts on top of the slides.
The chokes are independent spring close with a non adjustable link shaft to open.
Between this, one pilot jet and fluting around with the timing and the air with the vac sync set up to monitor. It's.. so far good. Back to the restore thread. ... and to get fuel.


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