Kz900 won’t rev over 3k

[kev edwards]

Quick question if anyone is still watching this thread, the bike is running ok now but I have noticed the vacuum caps between the carbs and the engine are full of petrol. I have seen this before but thought it would stop when I started riding it. Is this normal? Or is there still something wrong? Maybe float level too high?
Thanks
Nick

Pretty much normal, i should imagine the vacuum from the motor when running pulls the atomized fuel across the internal hole and as it hits the forward edge turns back into droplets and settles in the stub and cannot be drawn out again.

[Nick.s]

Thanks Kev, I was thinking I would have to pull the carbs out again.
Good news
Nick.

[Nick.s]

I thought I’d cracked it but these carbs won’t give in, I set the mixtures with a colour tune and things seemed okish. Very slight bogging just before the mains take over, but rideable, it’s perfect on mains pulls really well. The problem is that the screws are only 1/2 turn out on all 4, and the spark plugs are quite dark brown. So I thought just turn the screws out 1/8 turn and check plugs again after a ride, the bogging got worse. If I open the choke when it’s bogging it gets better, so why are the plugs very dark like it’s running rich? I had the carbs out on Saturday to make sure the pilot jets (17.5) and passages were clean, no problems there. I just don’t know what to try next, I’m confused.
Any ideas would be appreciated
Thanks
Nick
(This thread is turning into a novel)

[zed1015]

Unless you are doing plug chops and killing the motor at higher rpms, the plug colour only indicates the fuel mix at tickover.
The choke test indicates a weak mix on the transition to the main.
I presume the mix screws you are turning out are the air screw on the side which also worsened the bogging by weakening the mix further and confirming the problem ?

[Nick.s]

So why are the air screws only 1/2 turn out? And why are the plugs very dark? If the mix is weak surely the plugs should be light colour?

[zed1015]

The plugs are showing dark only on the pilot mix and this is showing rich because the air screws are in too far.
The plugs colour only indicates the mixture strength of the fuel circuit that was active at the time the engine was stopped.
You have a weak mix on the transition to the main by the sound of it and the rich pilot is masking it slightly hence it worsening when the air screws are wound out to where they should be.
The condition sounds just the same as when fitting pods ( which the air corrector jets would cure ) but you still have the airbox.
This is the area controlled by the jet needle and needle jet tube so that is where you should be looking.
You should do a plug chop and kill the engine under load at the point where the engine bogs to see the real story.
Bring the air screws out to middle of the stock settings and then lift the needles a groove to bring more fuel in earlier.
Hopefully that should make an improvement.

[Nick.s]

That makes sense, I’ll try that later.
Thanks mate
Nick

[Pigford]

Are the emulsion tubes & needles original (old).

These will wear over time and cause RICH conditions at the early opening stages.

[Nick.s]

No all new keyster kit.
Iv just done what Rob suggested, lifted the needles a notch. Although it still bogs a little bit the mains take over earlier now so it isn’t such a problem. The air screws are 1 3/4 turns out at the moment and the plugs are going a nice light colour, with a bit more tuning it should be lovely.
Thanks guys, ( especially Rob) keeping everything crossed for a bit.
Nick

[Nick.s]

Just been out for a ride, amazing, no spluttering or bogging just smooth and lovely. Rob your a genius, this club is lucky to have you around.
Thanks again
Nick.

[ADRIAN H]

Job your a genius, this club is lucky to have you around.

+ 1 for this sentiment. Top guy.

[zed1015]

Thanks, Nick.
No problem, glad you got it sorted.
I was just posting another reply which got held because of your new post.
I'll still post what I wrote below as it covers a few more options if needed and may be of use to others.
Cheers.

"I assume the airbox is stock and not modified for more air as a custom air corrector may be the solution if that's the case.
You still have another notch on the needle for more fuel but ideally you shouldn't have to do that and just richening up on the air screw to say 1-1/4 out may plug the gap.
If you can't quite iron out the issue you could try richer slides if you have them in any of your spare carbs.
Richer have a shallower cutaway and lower number stamped underneath.
So if you currently have 2.0 slides fitted then 1.5's would richen up the bottom end.
You would have to tweak the air screw to put the pilot mix back."

[Pigford]

Rob you're a genius, this club is lucky to have you around.

+ 1 for this sentiment. Top guy.

He's a canny lad that Rob, for sure

[Nick.s]

Thanks for that rob, iv got the screws set at 1 1/2 turns out and all is well. Iv just come back from a 50 mile ride and loved every minute of it

[Nick.s]

Anyone know how indie500 got on with his problems ?
I hope he sorted it, it’s worth persevering.