Z1OwnersClub GB

OK, so just a niggling issue.
When warm the J idles nicely at ~1000rpm and pulls cleanly when riding.
At a standstill, if I blip the throttle and then let it go it tries to stall (sometimes succeeding) before settling down to an idle again (this can take several seconds).
Standard CV carbs and airbox.
Carbs have been balanced and valve clearances checked.
I’ve adjusted the throttle cable and the idle screw sitting between the 4 carbs.
It’s always done this since I’ve had it. Any suggestions?

Rick.
You need to determine whether it's a momentarily lean or rich condition causing the problem.
Rich will bog the motor, Lean will starve but both will result in similar symptoms.
Blip the throttle while simultaneously feathering the choke ( enrichener) .
If it clears the problem you have a lean problem and if it kills the motor it's over fueling and then you know what you are dealing with and where to start.
Also has it ever has pods fitted ? and shows signs of rich running or not needing much choke..
If so it may have air corrector jets fitted that need removing now the airbox is back on.
On CV's they will all be in the mouth of the carb at the 4 o'clock position in the needle jet air bleed .
They are easy to spot.. Brass M5 slot head screws in jets..

Thanks, I'll give the choke test a go.
Bike is a US import which I bought direct from Kipkawa a few years ago before they stopped trading, so no idea whether its ever had pods fitted.
The other slightly odd thing is that when hot it will re-start easier with no throttle, but struggles with a slight throttle opening.

That does sound like over rich issues.
When hot the choke isn't needed and if activated would bog the engine, same goes for giving it throttle on a hot start supplying too much fuel.
If the choke test points to that then look for the air corrector jets and if it isn't that then the bottom end jetting may need leaning off.

A quick update.

Feathering the choke on the J carbs is not very precise as the choke lever slides out to the left and has 2 "positions" (notches denoting full and half choke). Just tweaking the lever as little as possible raises the idle to around 1300rpm. With this the engine responds and settles normally (back to the slightly higher idle). Pushing the lever back in (i,e, no choke) causes the spluttering/stalling and a bit of spitting back through the carbs.
This sounds like a lean condition problem ?
The only non-standard part is the 4-1 exhaust (currently Delkevic, although this issue existed with the Kerker lookalike replica it had previously).
I guess I just need to do a full strip down of the carbs and make sure everything is set to standard?

Yes! Spitting back indicates lean so possibly tweak the pilot screws to richen up the mix.
Also worth checking for any restrictions or blockages in the pilot system or pilot jet too small.

Thanks for getting back so promptly, at least I know what I'm looking for now.
Great advice as usual

Just looking through the workshop manual, and it states that the pilot screws are not adjustable on US models. Mine was a US import, so I may not have too many options unless there's some way of "converting" them ?

The US ones were set at the factory (slightly lean to suit whatever altitude the bike was sold in) for emission regs and capped off to stop tampering.
Removing the caps should reveal the normal pilot screw and slot head.

I keep forgetting what a b*stard job it is getting the carbs off a J when all the rubbers are cold and there are oil cooler pipes in the way !
Anyway, carbs are off, and (if I'm looking in the right place next to the vacuum take-off ?) the pilot screws are covered with a metal cap. These seem pretty solid.
Is there an easy way of getting the caps off without damaging anything else?

The usual trick is to drill a small hole In the metal cap and use self tapping screw or similar to thread into the hole and pull out the cap with pliers or failing that use a small screw driver in the hole to lever it out.
Be careful not to damage the brass screw underneath when drilling.

OK, I'll give it a try.
Thanks again

Success
The pilot screw settings were all over the place, between half a turn out and 2 turns out.
Now all set to 1.25 turns out as per the manual.
I really hope this makes a difference !

Just to follow-up my last point, over the years the pilot screws had clearly gone out of sync after being set and sealed at the factory. I appreciate that the eco conscious Californians don't want folk messing with their pollution compliant bikes. But if your engine starts playing up you'd have no way of knowing whether there was an issue with the pilot system (without drilling out the caps) and you'd be stuck with a bike that wants to stall all the time (unless you up the idle speed and cause even more pollution !).

Rant over, thanks for listening

Carbs cleaned and pilot screws set to 1.25 turns out.
Bike started ok on choke after about 4 attempts.
No popping now, and definitely better when throttle blipped.
Still has a slight tendency to stutter a bit when hot, and didn't like to re-start without a dab of choke !
So still have a bit of a lean issue going on?

Which way will richen the pilot mixture i.e. screw in or screw out?
I guess this will depend upon whether they're pilot air or pilot fuel screws? (manual doesn't say !).