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Cleaning out an Exhaust Pipe
on a Moped or Motorcycle w/ a 2-Stroke Engine
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Technical Advice
*Warning: this is dangerous! Do not try this unless you are an accomplished torch person.
  • The oil burned with the fuel in a two cycle engine leaves carbon deposits inside the muffler area. These deposits can be very thick, and cause the muffler to be completely shut in some cases. There are no safe solvents that I know of to remove these carbon buildups.
  • If only the tip of the muffler is plugged, pick it out with a long thin screwdriver or drill bit.
  • If the carbon is inside the baffle units, it can only be removed by cutting the muffler in two with a hacksaw, cleaning it and welding it back together.
  • The other method is  using an acetylene torch. The torch method produces a large amount of smoke and pollution when done, so I cannot recommend it. It is also easy to overheat the inside of the muffler, burning out baffles and possibly burning a hole through the muffler. I suggest not trying this unless you are an accomplished torch person with a death wish.

But here is how you do it:
  • Remove the muffler from the moped and lay it down on the ground, as it will get red hot and shoot out sparks several feet, so make sure you are not around anything flammable. Do not do this indoors!

  • Using the  torch, and a small/ medium tip, put the flame very close, but not into, the tip of the muffler. after a few seconds, the tip should be getting red hot. Be careful not to melt the muffler tip.

  • Keeping the torch tip very close to the muffler tip, pointing the flame inside the muffler, turn off the acetylene knob so the flame goes out, and turn up the oxygen knob to increase flow into the muffler. This will cause the carbon heated with the flame to burn up, and you can regulate the speed of the burn according to how much you increase the flow of the oxygen.

  • To much oxygen pressure and you will melt your muffler into a puddle, so be patient. A red hot band will slowly move along the muffler, slowing down in the very thick areas, and the red hot area will go away when the muffler is clean.

  • If a lot of globs of molten metal come flying out, you are getting it too hot!

  • It is possible to get it too cold and the flame front will go out, so the best results come when you heat it so there is a good red spot, then slow a bit then heat it up again every minute or so. You must not stop flowing oxygen until the muffler is completely cleaned out, or you will need to restart it again with a flame.

  • If a muffler goes out, it can be hard to get the flame burning again since the carbon closest to the tip will have been cleaned off first. In this case, you may need to punch a hole in the side of the muffler to get a fresh start, then weld it shut when you are finished.

  • Some mufflers cannot be cleaned in this way, a sound deadening material inside will melt into glass marbles, and they will plug the muffler tip from the inside untill you cut it in half to remove them.  So, you may as well cut in half at the beginning and get it over with.  Yamaha mufflers are notorious for this melted packing, for sure the Razz, Zuma and Jog.    Most honda mufflers, like the Spree, Elite, Express, and pa50 respond well to this treatment.

  • The exhaust port is also a place to look for carbon buildup. You should be able to look into the exhaust port with the muffler removed and see the piston. The light coating of carbon that lines the port is not the carbon to be concerned with.

  • If there is a buildup, it will be right next to the piston, and in fact acting as a part of the cylinder, so the hole the piston is seen through is much smaller than the hole at the end of the port the muffler is mounted to.    It is possible for an exhaust port that should be a 1" diameter all the way to the piston be reduced in size to 1/4".  Most times this carbon can be removed by chipping it away with a small screwdriver or file, being carefull not to scratch the piston.

Scooter Therapy Inc
12 North Few Street  |  Madison, WI 53703    
toll free 1-800-411-1543  |  local 1-608-255-1520    

fax 1-608-255-1587  |  E-mail

Scooter Therapy Inc    

12 N. Few St    
Madison, WI 53703 

toll free 1-800-411-1543    
local 1-608-255-1520    
fax 1-608-255-1587    

Hours: M-F, 9-6 Saturday, 10-3  CST

copyright (c) 2000
Scooter Therapy inc.

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