TOPIC:

On a 1977 kz1000 with stock air box an exhaust
I am using a stock vm26ss carburetor . I will buy the premium keystrokes kit from z1 enterprises . If I go up two sizes on my main jet what size jet needle works best ? I will go up one size on my pilot jet . So 107.5 and 17.5 pilot .
Greg

With just a 1075cc overbore on an otherwise stock bike I have never had to change anything other than increase the mains.
I also suggest only changing one thing at a time so you know exactly what change made a difference.

Then you would try a 104 main first then see if that works correctly .
When does it become necessary to use a rich main jet needle ?

It's been my experience going up in bore size with no other changes requires no jetting changes provided the carbs were tuned correctly prior to going to the bigger bore. You won't ever need a richer jet needle unless you start doing some really drastic changes but by then you should have went to bigger aftermarket carbs.

Gdizard wrote: Then you would try a 104 main first then see if that works correctly .
When does it become necessary to use a rich main jet needle ?

What is your stock size main ?
US bikes are jetted different than UK., Usually leaner.
I'm guessing you are 102.5 stock.
I would then start at 107- 110 and work down.
You don't need to touch the needle and don't change the clip position.

It may just be me, but it seems like you are putting the cart in front of the horse. It sounds like you don't have the bike running yet correct? If not, I would go ahead and rebuild the carbs and do all the proper adjustments including syncing them and see how it runs. You have stock exhaust and intake components so you may not need to go larger on anything, but you won't know until you try it first. That way you have a pretty solid base line to work from, but as has been suggested, I would only do one change at a time and see what happens. Make sure all adjustments are made on the engine such as valves, timing, cam chain, etc. then go into carbs if needed. Don't forget the ignition advancer.
Rick H.