Cleaning The Top-End (Decoking)
This tutorial will demonstrate the process of decoking the top end, or removing the carbon deposits from the engine. This is a standard maintenance and should be performed every 6000km (4000 miles), or every year for machines that are never heating up (quick hops about town). It will be virtually impossible to get all the crud off of the engine parts, so don't be overly compulsive about it. Though the process seems daunting, like putting a wheel together, it is one of those chores that you will be able to fly through after your first go. I would give it a few hours for the first time. I hear some asking, "why should I do this; my engine runs fine?" This procedure is important because of the heat and power restrictions a two stroke engine has to contend with. By letting junk build up on the piston, cylinder and head, you are effectively decreasing the fuel capacity of your motor (ie 200 cc to something slightly less). Since waste carbon, commonly called coke, is left from burning two stroke oil, the engine will suffer from an overly "rich" condition and generally run badly or start hard. A few signs that your top-end may need to be cleaned are oily, constantly fouling spark plugs; hard starting (more than 4 kicks) and lots of exhaust smoke. I would reccomend you preced this operation with a carb rebuild when attempting for the first time. Synthetic lubricants will increase the period of this procedure, but it is still worthwhile to consider attempting every year. This procedure is best done in a covered, well lit area (like a garage) so no crap gets into your top end.Tools & Parts Needed
Spark Plug Wrench
Disposeable Shop Towels
A can of Carb Cleaner
A Tube of Anti-Sieze Lubricant
13mm and 11mm Deep Socket
Torque Wrench (Absolutely neccessary, DO NOT perform without this item)
Plastic Bondo (Body Filler) Scraper
Plastic "Wire" Brush
Tub of All-Purpose / Bearing Grease ("Green Goop")
Once all the panels are back on the bike, kick start the engine as usual. The engine should roar to life after a few kicks. If the kickstart lever doesn't feel firm or if the the engine will only run when the choke is turned on, you have an air leak. This will probably be caused by the sparkplug not being tight enough (*The plug is touchy, don't tighten it too strongly or you will rip the threads out of the aluminum*). If you did rip the threads, there will be a leak around the damage -- take the piece to a machine shop and have them install a "helicoil insert", and remind them of the fact it is a cylinder head so they can use a high heat transfer coil. This will replace the old threads and make a much stronger thread. If the plug IS seated properly, the cylinder head may be warped from improper tightening. IF YOU FOLLOW THE RULES, THIS WILL NOT HAPPEN. However, if it is warped, you will need some 400 grit wet/dry sandpaper and a piece of glass. Tape the paper to the glass and wet it. Hold the cylinder head in your palm and rotate the bottom on the paper until it is flat. Once you are done remount it and try again. This maintenance should be done yearly for year round riders, every 6000km (4000 miles) for the "rally only" types.
All Material Copyright 2001-2015 by Richard Hoar. Use at your own risk.