Alternative Carbs - Z1000 MKII

[HowieD]

Hi,

there's a simple remedy to this, sorted mine out in 1980 (!) and never had any trouble since:

get two lengths of reinforced petrol pipe and connect both outer & both inner inlet pipes together using the little pipes for fitting the carb balance gauges. they are on the inlet stubs between the carbs and the head - should have little black caps on them.

hope that helps

regards
Howie

[njwmct]

Hi,

there's a simple remedy to this, sorted mine out in 1980 (!) and never had any trouble since:

get two lengths of reinforced petrol pipe and connect both outer & both inner inlet pipes together using the little pipes for fitting the carb balance gauges. they are on the inlet stubs between the carbs and the head - should have little black caps on them.

hope that helps

regards
Howie

Howie - thanks for the tip - I certainly give it a try.

Did you have the same problem i.e a stumble / hesitation just off idle ?

[HowieD]

Howie - thanks for the tip - I certainly give it a try.

Did you have the same problem i.e a stumble / hesitation just off idle ?

Yes I did and the Kawasaki dealers in Lincoln at the time couldn't fix it either. In the end I wrote into Motor Cycle Mechanics and that was the remedy they came up with.

Also to drill some holes in the Air box transfer pipe but I didn't do that. It has individual filters on it now anyway.

H

[Garn 1]

HowieD, Pass this by me again.... See if I have it right?
Connect the nipple of the vacuum point on the rubber inlet-manifold of carb #1 to carb #4. Connect carb#2 to carb #3. I can see this would equalise the vacuum in the connected carbs.

Was the problem that NjwMct has/had, the main reason for solving this stumbling problem off idle or was there other problems it was designed to solve?

My only slight concern would be the longer length of tube to connect 1 & 4 which could affect the vacuum. However they could be made equal.

It is definitely worth a try. Sounds great! It may be a simple remedy for other problems in these 28mm carbs.

RegardZ.

[HowieD]

Garn1

you are right on all counts for the symptom and how the pipes are connected.

I don't think the different length makes any difference. I just cut the pipes to a length which allowed a wide radius bend.

a few years ago I added a Scott Oiler and fitted a Tee piece to the 1 to 4 pipe near the 1 end for the vacuum and that made no difference that I could tell either.

let me know how you get on.

regards
Howie

[zed1015]

Hi,

there's a simple remedy to this, sorted mine out in 1980 (!) and never had any trouble since:

get two lengths of reinforced petrol pipe and connect both outer & both inner inlet pipes together using the little pipes for fitting the carb balance gauges. they are on the inlet stubs between the carbs and the head - should have little black caps on them.

hope that helps

regards
Howie

What this does is create a similar effect to yamaha's YICS system or the Boost bottle mostly found on 2 strokes, drawing extra fuel from the other carbs intake when coming on load.
Connecting all the vac tubes with 't' pieces may increase the benefit slightly.
I have also experimented with small chambers linked individually to each vac take off, not as a cure for the idle flat spot though but to reduce throttle lag on acceleration.

[Garn 1]

...The jets goes in the air bleed to the needle jet/emulsion tube NOT the pilot bleed which is metered by the air screw.
Looking at the carb mouths (26 and 28 mikunis) they are positioned at 4 o,clock on the left hand pair (1 and 2) and 8 o,clock on the right hand pair (3 and 4).
There are no existing jets to drill out, which would be pointless any how as the new jets reduce the existing air supply.
The needle jet/emulsion tube comes into play just off idle at around 1/8 throttle , it is this point ( just off idle ) that is richened up to smooth the transition.
Also as a result it may also be possible to go down a size or two on the main jet.
Hope that makes things clearer.

Having another look at this mod, I have to say I was looking at the wrong side of the carb mouth. As Zed1015 states; at the mouth there is two inlets one at 4 o'clock and another at 8 o'clock. One side is the air inlet that can adjust air to the pilot jet and the opposite side has a fixed jet (hard to see).

Zed1015 proposes to tap into this fixed jet side (air inlet) and fit a threaded brass insert with a 0.6 mm hole in it to fit in front of the air path of the fixed jet. This would, as he says, reduce the air into the emulsion tube which is the upper part in which the main jet sucks thru. I think the emulsion part of this tube is not used as throttle is opened above 1/3.
Not sure how it would affect the over all function of the main jet. Worth a look as we can always remove the jets if not solving the problem.
RegardZ.

[zed1015]

...The jets goes in the air bleed to the needle jet/emulsion tube NOT the pilot bleed which is metered by the air screw.
Looking at the carb mouths (26 and 28 mikunis) they are positioned at 4 o,clock on the left hand pair (1 and 2) and 8 o,clock on the right hand pair (3 and 4).
There are no existing jets to drill out, which would be pointless any how as the new jets reduce the existing air supply.
The needle jet/emulsion tube comes into play just off idle at around 1/8 throttle , it is this point ( just off idle ) that is richened up to smooth the transition.
Also as a result it may also be possible to go down a size or two on the main jet.
Hope that makes things clearer.

Having another look at this mod, I have to say I was looking at the wrong side of the carb mouth. As Zed1015 states; at the mouth there is two inlets one at 4 o'clock and another at 8 o'clock. One side is the air inlet that can adjust air to the pilot jet and the opposite side has a fixed jet (hard to see).

Zed1015 proposes to tap into this fixed jet side (air inlet) and fit a threaded brass insert with a 0.6 mm hole in it to fit in front of the air path of the fixed jet. This would, as he says, reduce the air into the emulsion tube which is the upper part in which the main jet sucks thru. I think the emulsion part of this tube is not used as throttle is opened above 1/3.
Not sure how it would affect the over all function of the main jet. Worth a look as we can always remove the jets if not solving the problem.
RegardZ.

This is a very common, well proven mod that been around for donkeys years.
Every man and his dog fitted a ledar kit to cure this glitch when fitting pod filters.
It does exactly what it says on the tin.
it's easy enough to make your own, I have a selection i made in graduated sizes.
I start with the largest and work down till i find a size that cures the problem with the minimum restriction.
Most times though i do end up at 0.6mm like the ledar kits were ,maybe i have too much time on my hands

[Rich]

Basically you are reducing the size of the main air jet in relation to the main jet which will make the main system richer throughout. The emulsion tube and the needle jet are part of this system.

As zed1015 air corrector kits have been around for ages. I even have some Ledar stickers somewhere and they must be 20+ years old

[Garn 1]

Am I showing a lack of knowledge regarding these "Ledar" kits that Zed1015 and Rich have mentioned? I certainly am!
Anyone got a pic or an old ad or brochure?
Are they only for Mikuni carbs?
Only for the 28mm Mikuni?
Only for Z's?
What is in the kit? A tap? 4 x air jets?
What year did they come out?
What was the price (year) of the kit?
Was it only available in UK?

I'm starting to think that the later 79-80's Mikuni 28mm carbs did not have the fixed jet (at 4 / 8 o'clock) as mentioned and this was a mod for only the these later Mikuni's and not the early 28mm carbs on the Z1 series
RegardZ.

[Pigford]

Garn, Ledar did a range for different bikes that switched to pod filters - bit like Dyno jet kits, but a different angle

I think it was Leon Moss who developed them

[Rich]

It was - unfortunately he died.

[ruffle]

It was Leon; a really nice chap and great motorcycle engineer.

I well remember writing a program on a Sinclair Spectrum for him to record figures from his dyno runs and print out little graphs. In exchange, he build me a new 4 into 1 for my GPz1100B1.... which I gleefully fitted and chucked away the original exhausts Oh how times change eh?

[njwmct]

Hi,

there's a simple remedy to this, sorted mine out in 1980 (!) and never had any trouble since:

get two lengths of reinforced petrol pipe and connect both outer & both inner inlet pipes together using the little pipes for fitting the carb balance gauges. they are on the inlet stubs between the carbs and the head - should have little black caps on them.

hope that helps

regards
Howie

Hi Howie,
Just to let you know I tried this but unfortunately it did'nt solve the problem - still got the stumble just off-idle but I guess it was worth a shot.

[big green bus]

Leon Moss set my gpz1100 up years ago (he was the development engineer for BRM formula 1 racing car team) a very clever man, he also provided the BHP data for Performance bike mag & was the first guy who got CB900/750's to run filters with standard carb's using his LADAR INDUCTION KITS. As he explained to me the dyno read out for my bike talking about air temperature and pressure I looked on with a blank expression. It took years for me to understand what I was being told, but one thing stuck. He dyno'd my bike with oval K&N filters on 119 BHP, 125 BHP with Ramair foam filters & finally 115 with no filters at all so too much air is not always the way forward. Zed1015 is spot on you need the .6 restrictor to run filters properly.