TOPIC:

My 83 GPZ1100 (ZX1100 A1) has had the DFI replaced with
Mikuni BS series CV carbs.
The bike is good at idle and pull away, but as soon
as the revs climb around the 3000rpm range its almost
dies. If I keep the throttle open it'll eventually get
to about 4500 at which stage it pulls like a train.
I get the idea it is running rich, based purely on the
smell of the fumes.
The setup is as follows.
4 into 1 of unknown origin.
Pod filters
Ignition timing checked and spot on
Cam timming I have not checked as I dont have the
settings, but motor has not been openned to am
assuming this is correct.
Number 1357 E0x3 stamped on side of carbs
Pilot jet 37,5
Main jet 100
Needle jet 364 Y-6
Needle 5D 59
Needle clip on second groove.( I have tried moving
this up or down with minimal results)
Air screws all 2 turns out.

Any help would be much appreciated

Just a suggestion but if the cam timing were incorrect, your valves would be bent and your bike wouldn't start. I wouldn't concern myself with cam timing at this point. Once you figure out how to time the cams, you can check it when you look at valve clearances. It is FAR more likely that the valve clearances have closed up on a bike with little known history (you just bought it?). Also, check coil voltages. I have tech articles on valve adjustment (shim under bucket) and coil powering options on my web site.

As far as the issues with your carburetors, you need to rejet for the pod air filters and 4 into 1. I suggest you reclip to the 3rd slot and go with #40 pilot jets and #142.5 main jets. You can purchase the jets from www.z1enterprises.com. I have rejetted about 100 sets of BS34s in the past year with this combo using pods/4 into 1 and this is the correct combination. Should work well for you. You are definitely NOT running rich.

Thanks WG, will start with checking
clearances and coil voltages as per your suggestion.
I also need to balanace the carbs as their current condition is unknown.
Thats quite a leap in jet sizes from what I have, but
at this stage I will take advise from someone who knows
them better than I do.
You say you have done many of these..Are they good
carbs for the bike ?. I have the option of pulling the
Keihin's off my Z1R and using them.

The BS34s are excellent carburetors. They are sensitive to airbox and pipe changes and require rejetting more readily than perhaps some other type of carburetor assembly but once dialed in, power delivery is smooth and linear. They also still have an excellent variety of replacement parts which can't be said by some other types of carbs. I don't know what type Keihin carbs you have on your Z1R so I can't comment. My experience with Keihins is that their "round slide/mechanical slide" carbs tend to be somewhat overcomplicated and a pain to work on and the CV carbs (CV34) work well when dialed in but replacement parts are harder to come by; especially pilot jets (NONE AVAILABLE). The lack of pilot jets is offset by the dual main jet system which allows some compensation for the lack of pilot jet alternatives.

Ok will work on the Mikuni's for now. Going to get
jets tomorrow.
WG since you obviously know your way around these carbs, what sort of float level should I be looking at
and measured from where ?

The 34s have fiber floats with relatively flimsy tangs. This makes it critical to set the gas level using the service fuel method rather than attempting to adjust the float level statically. Put the carb rack level and put a clear hose on the drain. Turn on gas and then open the drain by opening the drain screw. Hold the hose next to the outside carb bowl and STEADY without lowering raising it any. There will be air bubbles in the hose. Tap them out or blow into the hose GENTLY till there are no more air bubbles. The gas will fill the hose to the level it occupies in the bowl. It should be about 4mm below the bowl gasket mating line. +/- 1mm is OK. If it is higher or lower, drain the bowl and remove it. Bend the small tab that contacts the float needle up or down to adjust the gas level. Bending UP will allow less gas in and conversely, bending down more. A small bend gives fairly large results so be conservative doing the bending. FWIW: 4mm is just a tad over 1/8" if memory serves. Also be patient as the carb will sometimes fill fairly slowly. Let the gas level stop rising before noting its final level. Recheck when you are done making adjustments.

Great, then they should be fine. I did them
that way and set the hight about level with where
the base of the bowl meets the retaining screws.
The air screws are running about 2 turns out.

Ok so I managed to get the 142.5 mains, it appears that
the Weber jets are the same. Haveing a torid time
getting the pilots, but even without them, I have
noticed an appreciable improvement.
Other than a dyno or CO2 analyser, what method would
one use to set the mixture screws correctly ??

The mix screws on the BS34 are not particularly sensitive or fussy. Start 1.5 turns out. Once the bike warms, try turning them in/out a bit for max idle speed (each) and adjust the idle down after each tweek.

Update:
Finally got some time to look a little deeper.
Coil voltage is great..
Found out from previous owner that the head had been
"done". This made sense as there was evidence of
removal. I checked the valve clearances and found
the following in thou:

Cyl___Out___In

1......5...2
2......5...5
3......4...5
4......6...1

So no problem, I remove the cams (under bucket shims)
and found that Murphy had not deserted me, only one
shim still had a number stamped.
So I guess I'll be sitting at the local bike shop
tomorrow with a micrometer and a bucket of shims.
I assume 2 for In and 4 for Out is acceptable ??

Anyway to get back to the carbs, I tooks the bowls
off , primarily to try and remove one of the pilot
jets that had a damaged head. After much patience , I
got it out and was surprised to see it was a #37,5.
Looking closely at the others, I saw that 2 were
#37.5 and not 17.5 as I originally thought, and the
4th was a#40. I will now have to get these replaced
with #40's, but now my flat spot is even less
explainable as incorrect jetting.
A quick check on the plugs shows that the cylinder
with the damaged jet was ok , but all the other 3
were very black.

Post edited by: BeemerBoy, at: 2006/12/14 15:46

Update.
Managed to buy 2 used shims I needed at a local
Kawasaki dealer. So cams back in place.
All exhausts are now around 6 thou and inlets
vary between 4 and 5. Timming checked.
Havent managed to get #40 pilot jets yet so
she still has #37.5's. Carbs balanced, and she
really purs like a kitten.
BUT... My flat spot is still there. Now would
the pilot jet size really cause it to be that bad.
From about 2500 rpm, she doesnt pull at all, in fact
if i'm up 3rd gear or higher, she will just about
come to a standstill if I keep her in that gear. I
have to change up at about 5-6000rpm to get anything
out of the next gear.At about 8000 again , she stops
pulling. There is not noticeable difference with or
without the air filters,and I can hear her sucking
hard through the carbs when the pods are off. Standing
still, she picks up very quickly without any symptoms.

I'm really getting frustrated as I want to start
using the bike for commuting. Tomorrow I am going
to put my Z1R Keihins on the bike and see how they
perform. They are mechanical slides.
Everything points to fuel starvation and yet I cannot
see why. Carbs have been stripped, cleaned and all
paths blown out with compressed air.
PLEASE HELP !!!!!!

BeemerBoy wrote:

...good at idle and pull away, but as soon
as the revs climb around the 3000rpm range its almost
dies. If I keep the throttle open it'll eventually get
to about 4500 at which stage it pulls like a train....
Ignition timing checked and spot on....

Just a thought -- is the timing advancer unit lubed and working freely --- thinking idle timing could be okay but advancer hanging up until reaching the 4500 rpm range.