I just got a new (200 miles) 04 that a guy had in his garage for 2 years. Seems he got it for his wife and she scared him by riding aggressivly (like that!).
Anyhow, got it running pretty well after he cleaned the carbs and replaced the gas. In the process though he noticed the vacuum diaphragm on the top of one carb has a 1 mm tear in it's very outer radius. I have noticed the bike idles very inconsistently very low early in the ride then too high later on. Could this be the cause and must I replace this part that goes for 120 bucks? Thanks in advance for help. Otherwise bike runs really well.
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When you say early and late in the ride it makes me wonder if it is properly warmed up. The bike is pretty cold harded and will idle low for about 5-10 minutes if you just let is sit and idle. Then it will start to idle normal after that.

Is your idle speed set too high and that is what is causing the problem?
Are you choking to start?
How is the gas mileage? (using too much?)

If it runs smooth with now major dips in the power, and you still getting 50+ mpg I think the diaphram is fine. Especially if the small rip is just on the edge/lip.

However, if it is genuinly inconsistant when warmed up and with the proper idle seting, you're losing power and MPG, then I would say you have yourself a problem that needs replacing.

Thanks for reply. Yes the idle runs higher when hot so maybe just cold blooded. I start with full choke and no throttle it's been cool in MA. I have fiddled with the idle speed…higher when slow and lower when fast. Mpg and hp seem ok I'm still waiting for reserve at 160 miles on first tank. With cold blooded bikes do you just leave the choke on for longer? I try to turn it off as soon as possible so I don't forget it.
Thanks
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If I am in a hurry then I will leave the choke on for a few blocks but only about a 1/4 choke. Yes they are cold blooded and that is what you are experiencing. Mine does the same thing. It's not just a 250 thing almost all the kawi's are cold blooded like that. Great machines but cold blooded.

You should open up the choke and let it idle until the RPMs start to climb. SLowly close the Choke as the engine warms up aiming to keep the RPMS arround normal idle speed. After a minute or two I have the choke completely closed.

Here is a good test. Start up the bike from raw cold, following this procedure. Once the bike has been idleing for 5 minutes, jump on and take a ride with minimal idleing for about another 5-10 minutes. Then pull the bike into your driveway and set the idle. Take another quick ride with lots of stops and idleing. Make sure the idle doesn't hang. If it doesn't go home and let the bike cool down. Once it is cold try starting it up, warming it up and riding. If it all seems okay, your good.

If you experience a hanging idle when warm or it is impossible to start once cold or you have some flat spots in power or the engine is bogging down heavily when you start from a stop, you have a problem.

BTW: If you do tear one of the diaphrams, talk to TheDuck (http://www.ninjette.org/forums/member.php?u=62) :p He has a pretty effective way of patching the diaphram with a rubber tire patch that sounds to work.
From: http://www.ninjette.org/forums/showthread.php?p=13431

+1 for cold-blooded bike theory. If I don't choke it enough or long enough, it's pretty fussy about RPM until it warms up fully. If you're not showing a severe drop in fuel efficiency, I don't think it's the diaphragm, but may be worth repairing it to prevent that rent from getting worse.

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Thanks all. May just repair diaphragm the next time I see it too be sure. Perhaps there is some idle hang in my case so may need a bit of tuning.
Great bike my triumph is jealous
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seems like every time I ride it, it gets better. Today the idle stabilized sooner and I didn't have to fiddle with the idle speed adjuster once. So maybe just overcoming the storage lesion of sitting with gas in it for a couple years...I hope so. I just filled it and got 56 mpg which I assume is OK esp since I was running it in hard. Just too much fun not to! I hope the mileage points to carb running OK despite tiny rent in diaphragm.

I am sure I need to pay some attention to a number of items that don't ordinarily show up at the 500 mile service because of the prolonged storage. Oil of course, coolant etc. What about brake and fork fluid? It is an 04 with low miles and indoor storage. Any other suggestions will help.

Also, I just installed a new shock (Hagon) and what a difference right out of the box!!! Thanks to Dave Quinn who answered all my questions and seems to be just a generally good guy. Imagine what will happen when I get some fork springs. and a jet kit and pods and a pipe and new tires and and and. As you know this can be rather addicting. Amazed that everything for the ninjette is so inexpensive compared to other bikes. Lot's of fun so far though.

Very glad to hear it! Mid 50's is pretty normal for ninjettes being flogged, but I think you'll get slightly better still to come if it stays stock.