Is it just slow? Or is it revving slowly? What's the history of the bike? Any modifications? Service history? Fresh gas? Etc...
It could be a number of things, carburetors, fuel flow issue due to faulty petcock, bad plugs, spark plug caps need to be cleaned, valve adjustment.
I'm sorry but the list isn't short.
If your in need of carburetor services PM @
ducatiman. I can personally vouch for him, along with other members here and over at EX-500.com his prices are highly affordable, cheaper than most shops, and turn around time is short.
Custom Carb Service
The other items such as plugs, caps, petcock is all easley checked.
Here a write-up on the cleaning the spark plug caps, I recommend changing the plugs with NGK Iridium plugs.
Even bad plugs should do something, unless they are totally shot.
Did you renew the HT leads, and disassemble the caps?
Make sure you disassemble the caps, and clean them, and yes the caps get cruddy.
Here my write-up,
Quote:
Short explanation: The inside of the hard plastic caps accumulate crud the can short out the spark. This can cause rough running or failure to start. Every time you do any work on the bike: remove them disassemble and clean them and renew the wires or at least the connections.
The long Explanation, Warning engineering information can cause Drowsiness.
The ancient cylinder design of the engine dictates that the spark emanate form the center of the combustion chamber. In order to get it there, the plugs had to be located down deep in a well between the cams. This well is a perfect place for dirt and moisture to accumulate. Then because there is no cooling water at this point the metal around the plug runs very hot. Surround this with the large amount of cool metal and you have a recipe for condensation. Now K did drill a drain hole between the fins to help (a little) but it often gets plugged up.
The moisture boils off the base of the plug and the vapor condenses on the cool plastic cap and the plug insulator. This moisture forms a easier path for the electrons to ground than jumping the gap at the plug to make a spark. Misfire.
This issue is right up there with Pilot jets as a cause of trouble.
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Here's some pictures that might be helpful. I took these when I replaced the wires themselves, as it was a good time for a write-up, and the wires were OEM from 1998.
Wires are just 7mm copper core, with clear silicone jacket
Testing the petcock, is easy, disconnect the fuel line from the carburetor, find a container, then start the bike, it should flow pretty quick, don't forget to check in both the run and RES position, then shut the bike off, no fuel should flow.
Another write-up
Quote:
If your petcock is shot, save your time, and money and get a new one, the cost of rebuilding it isn't much cheaper, due to you need two separate kits, as they for some reason don't make just one.
New one cost about $65.00
http://www.partzilla.com/parts/detai...1023-1139.html
Also be sure to order the orings(92022-183 WASHER,6.2X11X1.5)and new bolts(92001-1091BOLT,6X20),trust me you'll be better off in the long run.
Rebuilding kits are about $60 total.
K&L Supply Diaphragm Only for Fuel Petcock Repair Kit 18-6638 https://www.amazon.com/dp/B0055DWO60..._s1CGub1W9N3PH
K&L Supply Fuel Petcock Repair Kit 18-2723 https://www.amazon.com/dp/B001KO2JRW..._U1CGub05DT5NT
IMHO not worth it rebuilding, also be sure to check vacuum and fuel lines for wear, holes, and cracks, if in doubt replace them. Also replace the two small O-rings on the bolts for the petcock part# 92022.
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Odds are the bike was never properly serviced or taken care of, so I'd recommend a valve adjustment, you did mention the shop did a valve job, I'm assuming they did the adjustment.
Some Ninjettes live a poor and abused life, being an entry level bike.
SIDENOTE:
I did the
Kawasaki ZX Ignition Coil Pack modification to eliminate the spark plug caps problem, and a stronger spark.