Z1B-900 carb settings 29mm smoothbore

[Chris71]

Hello gents

Can anyone point m in the right direction? I have a 1975 Z1 with a 1075cc big bore kit running 29mm smoothbore carbs.
The bike has a standard airbox and exhaust but has been ported with street cams installed.
The carbs have 120 mains and the needle setting is in the middle.
When I got the bike it had a 4 into 1 & pod filters, the carbs had 25 pilots, to big I think? Now that i have gone back to a standard airbox, filter and exhaust.
I've tried 17.5 and it runs much better with no surging. The air mixture screw is only 1/2 a turn out, idles much better with only a very slight pop now and then.
Would I gain any more bottom end if I go up to a 20 pilot?
Is the air mixture screw ok being only 1/2 trun out and would the slight pop go if I went to 20's?
Anyone have any suggestions.
Cheers Chris

[zed1015]

Those smoothies are wasted using the stock air box and exhaust and you won't get much advantage if any over stock carbs with that set up.
The 120 main is also too big and you should drop to around 115 - 117.5 .
Airscrew should be opened to somewhere around 1 -1/4 out and the pilot should be left at 17.5 or even try a 15.
All this is a very educated guess as no one ever runs Smoothbores with a stock airbox and exhaust and the 1075 kit and cams will also not perform at their best like that.
Personally I would either put a decent pipe and pods on the bike or go back to stock carbs and jet up the main to suit the 1075 and cams.
Anything else is a bad compromise.

[Chris71]

That's what I am going to do, I am trying to hunt down a good set of original carbs. But in the meantime am trying to make this work...
It had pod filters and an exhaust before and it now runs better without all that crap on it & looks better...
It was obviously never set right in the first place, thanks for your input..

[Swirl]

Great question saves me asking it, mines 1045cc high compression forged pistons, ported head, Andrew's X2 cams, welded crank and plenty of other goodies again with 29mm smoothbores will be on pods on my Z1-R, have got a couple of different exhausts too although I want a Yoshimura Cyclone now at the top of the wishlist. What pods are best 4 singles or 2 doubles genuine K&N ???? Sorry for jumping in on thread but may as well get all the info in one place.

[zed1015]

That's what I am going to do, I am trying to hunt down a good set of original carbs. But in the meantime am trying to make this work...
It had pod filters and an exhaust before and it now runs better without all that crap on it & looks better...
It was obviously never set right in the first place, thanks for your input..

Ok. Smoothbores were never as good as they were made out to be and due to the main jet block insert causing turbulence weren't much an improvement over stock 28mm Mikunis in the flow department.
They are actually harder to tune and less responsive than a set of bored out 26mm's.
Aim for jetting similar to the 28 mikunis fitted to Z1R's etc and you should get close to decent running.
They are already equipped with a changable air corrector jet so any off idle fueling glitch can be tuned out with that.
Smaller to richen . Larger to weaken.
Feathering the choke ( enrichener ) at a given flat spot will give you an indication of which way to go.
If the choke clears the flat spot you need to be richer and if it makes no difference or bogs the motor you need to go weaker.

[zed1015]

What pods are best 4 singles or 2 doubles genuine K&N ???? Sorry for jumping in on thread but may as well get all the info in one place.

I personally would use individual filters but doubles probably won't make a difference once set up.
Have to say I have never used doubles on the slide carbs.
On CV carbs though dual pods do need to be used to make the best of a bad job .
CV carbs need still air for smooth operation of the slides which is why they never run that well on individual pods due to the separate intake pulses sending all the slides out of whack. .
Dual pods on those help smooth out the incoming air between each pair of carbs to dampen and cancel out the slide fluctuations.

[Swirl]

What pods are best 4 singles or 2 doubles genuine K&N ???? Sorry for jumping in on thread but may as well get all the info in one place.

I personally would use individual filters but doubles probably won't make a difference once set up.
Have to say I have never used doubles on the slide carbs.
On CV carbs though dual pods do need to be used to make the best of a bad job .
CV carbs need still air for smooth operation of the slides which is why they never run that well on individual pods due to the separate intake pulses sending all the slides out of whack. .
Dual pods on those help smooth out the incoming air between each pair of carbs to dampen and cancel out the slide fluctuations.

Cheers Rob, I know from the Suzuki's I've had on the twin pods, singles it is then, let's hope the 29's were worth the extra cash on top of the 28's I sold

[Chris71]

That's what I am going to do, I am trying to hunt down a good set of original carbs. But in the meantime am trying to make this work...
It had pod filters and an exhaust before and it now runs better without all that crap on it & looks better...
It was obviously never set right in the first place, thanks for your input..

Ok. Smoothbores were never as good as they were made out to be and due to the main jet block insert causing turbulence weren't much an improvement over stock 28mm Mikunis in the flow department.
They are actually harder to tune and less responsive than a set of bored out 26mm's.
Aim for jetting similar to the 28 mikunis fitted to Z1R's etc and you should get close to decent running.
They are already equipped with a changable air corrector jet so any off idle fueling glitch can be tuned out with that.
Smaller to richen . Larger to weaken.
Feathering the choke ( enrichener ) at a given flat spot will give you an indication of which way to go.
If the choke clears the flat spot you need to be richer and if it makes no difference or bogs the motor you need to go weaker.

Thanks great info I dont have any flat spots on acceleration at all and the bike pulls from 2k very strongly with the 17.5 pilots, but the top end I think could be better.
The smallest mains I have are 115 and I do have 117.5 aswell. I will drop down to the 115 and see if the top end improves.
Many thanks for the help...

P.s anyone for a set of 29mm smoothbores with K&N filters, I have the side panels to fit the pods for a Z1 aswell....

[Chris71]

Just an update..
115 mains 17.5 pilots carb balance and a tappet ajust.
The bike now idles without faultering at 1200rpm pulls from 2k and pulls my arms off at 6k and above, well pleased...
The bike runs beautifully in fact kept up with my mates Buell XB12S in acceleration to about 100mph from 30mph...
Happy days..

[zed1015]

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