zzr600 airbox causing splutter?

[mysterious_rider]

Hi guys, got my zzr on the road now and it will severely splutter if you try and go over 6krpm. She's restricted to 33bhp though.

it will happily go over 6kprpm without an airbox, why is it doing this? Is there anything else I can do other than run airboxless? Air filter is clean, and just to make sure I've cleaned it by hand.

cheers.

[jjdugen]

Is it a D or an E model? The E can be rekognised by the pointy frame member under the seat panels and air ducts in the nose of the fairing.

If an E then there is plenty for you to do.
____________________
The CBR900RR has been sold. Aprilia Falco worms its way into my heart.
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[mysterious_rider]

it's a 1995 E model. cheers

[Kickstart]

Hi

Check the float bowls are getting pressurised from the airbox. Not sure how it is plumbed in for that on the ZZR though.

All the best

Keith
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Traxpics, track day and racing photographs - Bimota Forum - Bike performance / thrust graphs for choosing gearing

[mysterious_rider]

You mean that little contraption that forces air through? Does it make a difference? I disconnected it for the time being. I'll connect it back up then maybe? Cheers.

[Kickstart]

Hi

Depends if the airbox is still pressurised.

Carbs work by causing a low pressure point at the jets (by a small restriction, which causes the air to speed up, and faster moving air has a lower pressure), so the normal atmospheric pressure acts on the fuel in the float bowl and pushes it through the jet.

If you pressurise the air through the carb then you land up with a higher pressure above the jets than normal atmospheric pressure, so no fuel gets from the float bowl.

Solution is to pressurise the float bowls by the same amount as the intake air.

All the best

Keith
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[mysterious_rider]

how would i do this? There is a tube that goes from carb to airbox. I cant remember If i connected it or not. Is it best just to block it off?

[Kickstart]

Hi

No, make very sure it is connected to the airbox.

All the best

Keith
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[jjdugen]

Oh dear, the idiot Kawasaki 'ram air' system strikes again.

Take off the airbox, pull the large rubber tubes that go through the frame holes off the plenum chamber in the fairing sides. Now get some spray can caps and wrap some tape around then until they sit firmly in the frame holes.
Now take off the plastic tapered tubing that sits on top of the carbs, but leave the two rubber tubes connected to the carbs.
Next, disconnect the small bore tube that connects with the fresh air gubbins on top of the motor (it connects to the carb inlet rubbers via a plastic T piece). Block that with a suitable stopper, a bolt is fine.

You have now disconnected all the things that cause rough running. The fresh air thingy causes the middle two cylinders to run slightly lean so you will need to adjust the air screws a half turn or so, listen to the engine, it will run smoother as you get the right mixture. There are some carb iceing pipes in the way but these can be eased clear of the airscrew outlet.

Whilst in there, you might as well replace the plugs and check the HT leads and plug caps for any cracks.

All the above is a good thing to do, but, just to save you a little time, make SURE that the choke bar is returning fully to the off position, even a slight bit of choke will give some really rough running symptoms.... dont ask how I know. ( well, I chased a rough running engine around the workshop for two days before noticing the choke was ever so slightly 'on', Ho Hum we all learn).
____________________
The CBR900RR has been sold. Aprilia Falco worms its way into my heart.
Try Soi 23 on Amazon for a good read.... Self promotion? Moi?

[mysterious_rider]

can that ram air really make a difference? It's mostly only in 1st gear. It just hesitates a lot around 4k after that it pulls really well.
Other gears seem a bit better oddly enough.

Also, when its cold and i just start it, a few minutes on choke isnt enough. I have to revv it up quite a bit before it will revv over 5k at all, if i hold the throttle on full it'll just stop at 5-6k unless its warm. then it holds at about 12k.

Right, so I'll refit the airbox tomorrow but block off the ramair. I'll just remove the tubes and stuff old shirts down the large intakes

Oh yeah that weird load of tubing going to the middle cylinders WTF Just WTF. They suck better than a thai hooker! So block them off too? I will give it a go.

[moppy]

I have a similar kind of problem with my ZZR6 E (99). Between 3 and 4K, there is absolutely no increase in power, feels very flat. But I think my bike is restricted, so it does make sense.

[jjdugen]

I shoud have asked what kind of exhaust you have fitted, too. The general opinion is that a four into one will give flat spots around 5K and 7K RPM. Mine did have that kind of hesitation with a Micron Nexus fitted, but the airbox work and some vary careful airscrew setups have eliminated that entirely.
Just to make life even easier for you, you can now safely disconnect the carb heating plumbing too, this gives really easy access to the airscrews.
It would seem that, when all the airbox/carb pressurisation system is new and properly sealed, it all works well. But, as soon as the ducting gets a little distorted it upsets the fine balance between air into the carb mouths and the air pressurising the float bowls. In turn, all the colder air from the front fairing scoops leads to the carb icing syndrome that these Kwaks are very prone to. With the airbox now breathing the warmer air within the frame, this does not happen any more.
Purists will say that cold air gives a better charge to the cylinder and this is true. However, carbs really like still air to breath rather than the turbulent stuff being forced in by the frontal air scoops.
Suffice to say, no other manufacturer has gone this route on carburettor fed engines.
____________________
The CBR900RR has been sold. Aprilia Falco worms its way into my heart.
Try Soi 23 on Amazon for a good read.... Self promotion? Moi?

[mysterious_rider]

Cheers.

Right I will do this today!!

I'll leave the carb cooling on for now, unless It's required to remove?
Seems like the whole air ram idea is a bit stupid really. Just aint workin'

also the exhaust is the standard 4 into 2 system. So twin cans.

I'll close it all up soon, I'll report back today.

[mysterious_rider]

Hi mate printed out what you said and followed it to the letter. You were BANG ON! Bike runs like a dream!!!!! Airbox is all on and sorted and it runs really well. You absolute legend!

thanks matey!

[jjdugen]

Thanks and a good job well done. Please tell Sickpup who thinks I am some kind of back street bodger.... Well... I do work in a backstreet.... and I suppose.......
____________________
The CBR900RR has been sold. Aprilia Falco worms its way into my heart.
Try Soi 23 on Amazon for a good read.... Self promotion? Moi?

[mysterious_rider]

Well it worked mate. So I'm happy. Will go and take her for a proper good spin now.

[Kickstart]

Hi

It should work with the ram air in place.

However Kawasaki tended to jet their bikes to run at the lean end of normal. Fine normally, but anything that makes them run a touch lean (build up of cack in the jets, etc) lands up making them run too lean

All the best

Keith
____________________
Traxpics, track day and racing photographs - Bimota Forum - Bike performance / thrust graphs for choosing gearing

[mysterious_rider]

[jjdugen]

As I've said many times before, the little ZZR is a damn good bike. I bought mine as a £400 ratter to do up and sell on. Suffice to say its stilli in the garage. Mine came with a rough running motor that I initially put down to gummed carbs and dud plugs. It took me a good month or two of trying various fixes before I went the route I described. Basically, you are putting it back to 'D' spec, which is no bad thing.
The trouble with forced induction on carbs is that the incoming forced air is trying to push the mixture back down the jet tubes. So you have to counter this by pressurising the floatbowl by the same amount. All fine if the balance is kept, but hoses leak, airboxes distort, air filters become less porous, the balance can go out too many ways for my comfort. A bit of judicial pilot screw adjustment and you have a powerful and smooth motor. Spend a bit more time on suspension tweaks and the Z is just about the most accomplished of the affordable bikes out there.
____________________
The CBR900RR has been sold. Aprilia Falco worms its way into my heart.
Try Soi 23 on Amazon for a good read.... Self promotion? Moi?

[Kickstart]

[mysterious_rider]

Cheers guys. Done over 150 miles on her and it's ace. It's not too bad on petrol either!

gotta sort out a few pieces, namely warped front discs.

[podge1967]

jjdugen

Think your onto summat there, i have a zzr 600e7 that has caused me no end of problems since i changed to s/s headers, which meant stripping down the front end, could i have missed a ram air pipe when i put it back together ?? it seems to stutter at 8-9000rpm in 6th effectively restricting the bike to 90mph unless i gear down to 4th and leather it which isnt really how it was designed to be ridden. Does the ram air system cause this if it isnt right ?

Thanks

[mysterious_rider]

[Kickstart]

Hi

Are they standard headers? Or an aftermarket 4>1 system?

All the best

Keith
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Traxpics, track day and racing photographs - Bimota Forum - Bike performance / thrust graphs for choosing gearing

[sickpup]