F650 Cylinder Cleaning FAQ

compiled & edited by Kristian #562
Please read the Disclaimer before attempting any work in this FAQ.
by Flash#412, October '01

Also see the following FAQs:


Do NOT Try this unless you know what you are doing!

Prompted by this Request

"I've been having trouble starting,needing more and more choke even as summer approaches. I grabbed the first bottle on the shelf with petroleum distillates (read ligroin -- it's more fun to say). After four tanks using a quarter of the bottle in each tank, it starts easier and runs smoother. There are those who swear by techroline, a synthetic amide polymer but other than that there probably isn't much difference between the rest with one exception. Methanol additives vs. ligrion additives (read petroleum distillates -- this is a family message board), the first helps with water, the second with the build up of creosote (read tar -- the "less" volatile components in gasoline). Neither survives combustion, so neither probably helps clean out the cylinder.

There is talk of cleaning out the cylinder by adding water at the air filter which turns to steam in the cylinder and powers out the charcoal build-up. Not exactly an additive unless you add it to gas with MeOH. Hmm, I wonder how that would work. Two liters of gas, half a liter of water and enough methanol to solubilize. Would it make enough steam to clean? Anyone else want to try? I've just been burned playing chemist on vehicles but that's a story that doesn't involve a motorcycle"

So, this is how Flash did it


  1. Turbo-charged motors that use water injection for anti-detonation are clean as a whistle upon teardown.
  2. The cylinder which sucked coolant via a blown head gasket is always simple to identify because it is carbon free.

Based on these two points and some advice by folks who had tried it, I very slowly poured about 2 liters of water through each jug of a running R80G/S. Sounds like rocks are in there. Don't pour it too fast. MUCH steam comes out the pipe. I thought I would see black stuff, too, but didn't. Peering in the spark plug holes indicated that the carbon was gone. I changed the oil later that day.

What I did was take a two liter soft-drink bottle and fill it up with water. I took the airhead carb intake elbows loose from the air filter outlets and turned them so they were facing up. I started the bike, warmed it up and then ran it about 2/3 of the way to redline. With my finger stuck in the neck of the bottle to limit the flow, I poured the water in as fast as I dared. More water slows the rpm, so you do this juggling act between throttle and bottle. When I finished with one side, I did the other. When I was completely done, I changed the oil.

Since then, I have read that you should use a spray bottle, like you can buy at the hardware store or recycle from a cleaning product. Your hand will get tired, but there is NO WAY you could add water too fast and hydro-lock the motor. Water is non-compressible and if you get more in there than the volume of the compression chamber, you'll bend a rod.