What is the adjustment procedure?
For you visual learners, here's an article from How Stuff Works. If you click on the first picture, the animation will give you a very simplified view of how the cams work. Note that when the lobe is against the valve (down) the valve opens. You don't want to adjust the valves while they're open. When the heel is on the valve, the valve is closed, and you can check your clearance and adjust, if necessary.
Getting to the valves
This is all the stuff you have to do to put yourself in the position where you can actually do the adjustment.
Put the bike on its centerstand. Take off the lower and upper fairing, side covers, and fuel tank. Carefully pull the spark plug wires by their boots, and remove the left and right coil packs (two 12mm bolts each). Note when reinstalling them that the red wire goes on the bottom on each coil.
The service manual suggests draining the coolant so the radiator can be removed to make it easier to reach the exhaust valves, but it is possible to avoid this by removing the fan (3 small bolts and a wiring harness) and unbolting the radiator (4 bolts plus two that hold the filler neck). This grants better access, since the radiator is free to flex by its hoses (the coolant hoses will keep the radiator loosely attached to the bike).
You can also remove the 'wings' from which the front of the engine is hung (one long 14 mm bolt, the four bolts holding the two ignition coil brackets, and the two lower radiator bolts), which makes it much easier to reach the exhaust valves and makes removing the valve cover a no-brainer (otherwise, it requires some finessing to get it out.) This results in a huge gain in access, plus allows the cover to slip out without the use of four letter words! Doing so is highly recommended.
The long bolt is the front engine mount bolt. That and the four bracket bolts should be torqued to 24 ft-lbs when you reassemble everything.
Circled in red are bolts that should be removed from the left-hand side.
And, from the right-hand side:
Remove the alternator cover and flywheel view cap on the left engine side cover. Use a nickel in a pair of vice grips.
Many people try to remove the view cap with a screwdriver. This is NOT recommended. A screwdriver blade will generally not be wide enough to do the job without stripping out the slot. Note the photo below. This shows the damage that can occur from using something with not much blade width (like a screwdriver).
A good alternative is a drag link socket, such as this one from Snap-On.
Take out the two spark plugs. While this is not mandatory, it does make the job much easier. It lowers the compression of the engine to essentially zero, making it easier to turn over and more likely to stay the way you left it (instead of trying to turn over a bit more due to air compression.) This also means you should replace, rather than re-use, the plugs' crush washers, which essentially means putting in new plugs. This isn't mandatory, but the torque spec of "finger tight plus 1/2 a turn" no longer applies once the gasket has been crushed, so you really have to be careful re-using them. So, it is highly recommended that you put in new spark plugs after you adjust the valves.
Take off the four valve cover bolts and lift off the valve cover. Do not remove the cover gasket; leave it on the top end of the engine. Pay careful attention to the two rubber gaskets around the spark plug holes, #11009A in the diagram. These can sometimes fall into the engine while you're removing the cover.
The actual adjustment
Insert a large socket driver into the the left cover housing. You will use this shortly to turn the engine, using the alternator bolt inside. Just get it in place for now.
Kawasaki Recommended Adjustment Method
It is worthwhile to note that, with one notable exception, all of our experienced members think this method is difficult, confusing, and a waste of time. For an alternate method, please skip down to the N250RC Members' Adjustment Method. For more help with the factory method, please see your service manual.
Turn the bar forward (counter-clockwise) until the cam lobes over the left cylinder point out and slightly up. They should mirror each other, as in this image:
When this is done correctly a "1T" mark will be visible on the flywheel through the view hole (you'll need a flashlight to see it) and the tappets below the cams will wiggle when you try to move them under your finger. Note how it reads 1|T .
Here is a photo of the engine at TDC for cylinder 1:
N250RC Members' Adjustment Method
Going through this whole process of trying to find the 1T mark may be confusing. Many experienced riders say it doesn't really matter what your flywheel says, as long as the cam is not pushing down on the rocker arm when you adjust it. Turn the crank counter-clockwise until the lobes (the pointy part of the cam) are pointing up for whatever valve you're adjusting. Make sure the rocker arm is fully unloaded and the lobe surface is as far away from the rocker as it can get. Rotate the crank counter-clockwise as needed to point the lobes away from the rocker arms as you work your way through the valves. When the valve is ready for adjustment, the lobes will point up like this:
Get the cam lobes in the right position, then adjust just the 2 valves associated with those 2 lobes.
You may find it easiest to do things in this order:
Turn the crank and double-check them all again after you think you're done.
When doing it this way, the lobes will point more upwards than with the factory method. You also won't have to remove the flywheel view cap. Everything else, except for trying to find and line up the little marks, is the same.
Back to the regular adjustment article
So, you have everything in place and are ready to go. Now, take out your feeler gauges and slide the proper gauge finger under the first cam (of four for that cylinder), between the cam heel and the top of the valve tappet. You are supposed to slip the feeler gauge between the actual camshaft heel and the part of the rocker that the cam lobe pushes on.
The feeler gauge should slide in with little effort and drag slightly when the clearance is correct. The factory clearance specifications are .08 - .13mm (0.003-0.005 inches) for the intake valves and .11 - .16mm (0.004-0.006 inches) for the exhaust valves. It is easy to accidentally use an inch gauge instead of a mm gauge, so make doubly sure you're looking at the right numbers. The feelers should be thin and flexible, not thick and stiff.
If the clearance is not correct, grab a long 1/4" drive 9mm socket and loosen the tappet locknut; there's a small screw on top of the nut.
Use a very small flathead screwdriver (an eyeglass screwdriver works great) to turn the screw out a bit until the clearance is correct (if you use the looser end of the acceptable adjustment range, it will take longer before the valves need adjustment again.) Note that you shouldn't need to turn the screw much at all; if you're turning it a lot, something's not right - double-check the cam lobe position and your feeler gauges.
Rotate the engine again until the right cylinder cam lobes (above) are in the proper position (a "2T" mark will be viewable on the flywheel, for those of you using the factory method) and repeat the check/adjustment process. If the exhaust valves need to be adjusted, you may need to move the radiator and fan out of the way (see above). The exhaust valves tend to take longer to work on.
NOTE: Torque value for tappet locknuts: The original manual says 14.5 ft/lbs. The supplement says 13 ft/lbs. It's recommended to use about 12.
Wipe the valve cover gasket clean of oil and put everything back together carefully when done. Use very little torque on the valve cover bolts; the book calls for 87 in/lbs (if you don't have a torque wrench, then tighten them by hand followed by a 1/8 turn with a 10 mm wrench to seat them).
NOTE: You should sync your carbs right after you adjust the valves.
Other Valve Adjustment Articles