If my mileage per tank has decreased by 30km

[3L4NS1R]

Did you check if you were changing measuring systems? A DJ128 is a lot bigger than say a Mikuni 128.

Pull the choke on to add fuel; if performance improves you were lean. Take the airbox lid completely off to add air; if performance improves you were rich. Crude but may work; some of the best dyno tuners use it.

Would have to be a long way rich (for a long time), but possible with a DJ 300 kit in a 250. Depends how well tested the published mods are... this has come from advrider or some other source, right? Empirical data is usually more accurate than emotive.

There is heaps of stuff on the interweb about tuning. Sites like thumpertalk have "how to" documents which can be a great help, often 'stickies' at the top if there is not a specific tech forum. You could even try ktmtalk, as the basic information is the same. I don't frequent kawasaki forums so can't comment on them, but chances are they'll have similar info available. Also try your local library, they should have a few books on tuning; I found a couple that were recommended on thumpertalk.

Cheers for that advice! Will try the choke and airbox test...

Yes, these mods were done from recommendations from kawasakiforums and thumpertalk, and most recommended the 300 kit, as the needle has a better (more aggressive) shape.

[NordieBoy]

Did you check if you were changing measuring systems? A DJ128 is a lot bigger than say a Mikuni 128.

Mikuni 128 is bigger than DJ 128.
Mik 142 = DJ 150

[warewolf]

Mikuni 128 is bigger than DJ 128.
Mik 142 = DJ 150

Is that universal? I was pretty sure with my Triumph kit it was the other way... gonna have to go look now.

[3L4NS1R]

Here was me thinking the number was a fraction of an inch or something constant like that!

[warewolf]

Mikuni and/or Keihin use mm2 (millimetres squared) * 100, as the cross-sectional area of the jet. eg a 128 is 1.28mm2. you can probably check that on some web site.

DynoJet (I thought) use a flow-rate number, litres per minute of some fluid at some pressure... or % versus some standardised jet... something like that. Possibly in some arcane imperial units, too. Part of the reason is to protect their intellectual property, make it hard to cross-reference their parts.

[3L4NS1R]

So, getting back from melbourne, I've done two tests:

Pulled the choke out. This resulted in the problems getting worse, with the bike threatening to cut out and stall.

Took the airbox lid completely off. This solved all problems being experienced, improved performance through most of the ranges (bottom range is a bit weak still), and made the bike sound far healthier.

I think I have found the problem.

Thanks for all the help people! The choke test was the winner on the day!