The exhaust of a 2T engine consists of the pipe, silencer can, and the packing inside the can. When we run an overly rich air/fuel mixture,(meaning how the carb is jetted for whatever the ratio is), there will be residal unburnt oil and components from the fuel that will coat and start to fill the expansion chamber of the pipe. This unburnt "spooge" will also collect in the silencer packing and help to clog it up.
After you have run for awhile on an overly rich mixture, the residual carbon and goo living in the exhaust, will continue to exit for quite some time, even if you have sorted the jetting out and have a cleaner burning air/fuel ratio in the combustion chamber, the old oil will still be spooging out the exhaust as if it were still running very rich. Many will make the mistake of continuing to lean the mixture out simply because they still see smoke coming out of the pipe. Often times leaning the mixture out to dangerously lean conditions.
If you feel that you have the fuel/oil mixture where you want it,(I would never use less oil than you are now..in fact I run small bore 2T engines with 20-26:1 ratio always)
and then have the jetting sorted out in all circuits so that you are providing the combustion a good air/fuel ratio, then you need to get your pipe cleaned.
You can clean a 2T pipe out with eazy-off oven cleaner and a garden hose, but this is not a very efffective way to get the pipe spotless. Another way is to take the pipe to a radiator shop and have them boil it out. It will be clean as a whistle afterwards.
Then you need to repack the silencer can. Although some have used regular rolled up fiberglass from home depot for this...it is best to purchase some real silencer packing.
Follow the instructions on the package, or just mimic how the old oil soaked packing was placed in.
This will make it so that you can see the results of your labor without the smoke of old work.
I want to also add a couple of old articles. Both by bike legend Gordon Jennings. (oldies but goodies)
If you do anything, read up and learn to properly jet the carb at all circuits. Doing so will provide you with the tools to make the cleanest burning, most powerful engine it can be.
http://www.strappe.com/plugs.html
http://edj.net/2stroke/jennings/oilpremix.pdf
Just an observation...
But if you were jetted up properly when using the 20:1 ratio, then switching to a 50:1 ratio without changing the jets and metering devices will net you a very rich running engine. You have effectively added more fuel to the mixture at burn than the 20:1 provided.
Now if you were indeed jetted close with the 20:1, you could simply return to that ratio and will be much closer than you are now. Or you will need to change all the devices when using a richer fuel ratio like 50:1
Understanding how the oil/fuel and air/fuel ratios relate to one another, and how the bike responds to jet changes is key to providing the most performance for the 2T engine.
