Carburation?.....

[Johno23]

Hi guys,I’m new on here,I did introduce myself yesterday with a pic of the new to me Z1B.
Bike is by no means immaculate but is fairly original and unmolested.However, the bikes starts and rides pretty well, but, when you’re coming down through the box if you blip the throttle, it doesn’t really respond, or at least is slow to respond. Plugs looked a little rich on examination.I don’t know a great deal about these carbs at the moment but did have a similar problem with carbs on a t140 which had mk2 Amal’s on it. The choke plunger on that has a rubber seal which either degrades badly or just doesn’t sit probably.This obviously causes a very rich mixture which bogs the engine down.
My question is,is there a similar choke system on these mikuni’s which could cause a similar problem,or is there any other common problems that you guys know of that could be causing this issue.
By the way, this is probably the first of many requests for help!
Thank in advance

[Johno23]

Edit: bike is fitted with Dyna electronic ignition..

[zed1015]

The problem could be attributed to other issues such as over jetting, carb wear, sticking ign advancer, cam timing a tooth out etc but Yes! the choke plungers on these have a swaged in rubber seat which does degrade and go hard allowing excess fuel to bleed into the system.
This is an often overlooked cause of unsolvable rich running and usually gets blamed on something else.
Unfortunately the rubber seat is not available as a separate part and these early choke plungers are NLA.
By coincidence I am currently working on a system to replace the old swaged in seats with Viton which I hope to offer to members as a refurb service.
I have successfully developed the tooling to manufacture and press fit the new seats and I've just got to come up with a technique to get the old seals out that doesn't take all day.

[Oldspot]

Hi, I had a similar issue on my Z1 (72). I eventually solved by:
1) changing the ignition system to Dyna S just to eliminate the variability of points
2) making sure my float heights were spot on
3) ensuring good plugs
4) checking the jetting sizes and setting to standard

There are lots of variables so my approach was to try ensure minimise any variability.

You could be correct about the seals of the choke components; I did remove and clean these up but as stated I could not find any replacement seals/seats.

I might add that I was new to the Z1 engine and so I am just saying what I did, right or wrongly, but it has worked for me; I am no expert!