Z1OwnersClub GB

Hi all, I’m running a set of VM28SC’s, circa 1975 as the have an adjuster screw on number 4, on my MK2/LTD engine. Carbs have been rebuilt with new EBC/Mikuni jets 102.5 main and 15 pilot, new float valves and the choke plunger seals done. Air screws set at 1.5 turns. Basically the problem im having is with cold starts. Bike takes a couple of seconds to kick in on all four and i get lots of spitting back and popping. What I’ve noticed is that there is a lot of movement on the slide actuating shafts and I think the seals might be toast. Has anyone got experience of replacing the seals? Are they O rings? Cheers

Your jetting is vm24 650 sizes which is too small for 1000cc. You've got bigger throats with smaller jets.
Spitting back through the carbs is mostly due to a lean mixture/air leaks.

Maybe (see attached), and obviously I know about the air leaks because im posting about the actuator seals which will affect the vacuum. I was hoping someone might have changed the seals and might be able to help regarding where to source replacements. Bike actually runs and starts well when warm and no sign of lean mixture except on start up

If your asking about the seals on the throttle slide shaft/carb body, I've never seen a rack of carbs that needed them replaced. Any air ingress there would need to get past the slide to reach the throat.
After all, carb syncing is done without any carb body cap on with the later bodies with no detrimental effect.
Have you cleaned and checked the enricher brass tube of any partial/blocked passages
Also the pick up port in the bowls?

Not on the later Z1B carbs Warren, they have a screw and lock nut syncronising set up so you don’t need to take the top covers off. Unlike the later z1000 carbs, they dont have an actuating rod operating all four carbs, there is a linkage that serves two banks. I put grease over the area where the shaft goes into the top of No 1 carb yesterday and it seemed to smooth things a little. It just got me thinking that maybe it could cause a problem, but I could be wrong :-)

Yeah, I know. I was using the later carb syncing as an example that even without the top cap on it made little or no difference to how the bike runs.
Therefore those seals being a less than perfectly airtight is not your issue.

I know these Z1B carbs are a pig to get set up right so i might try and find a set of pumpers to stick on it. I reckon they are better carbs and Ive got a lot more experience working on them. Cheers

I'd go for a stock set of 26's there's plenty off them around. Nice n simple as you say.

Warren suggested a weak mix causing the spitting back. The table suggested the air screw 1 1/8 from fully in , and you have them 1 1/2 out you said. That would make the closed throttle mix too weak , by flowing more air