Hello, me again

 I have a plugged up silencer on my 77 dt250. How would I best clean it out and re pack it. I have never re packed a silencer this old before. 

 I want to keep it quiet of possible. I know I can burn the packing out and re paint the muffler, but I want to re pack it if I am able and if I don't need to burn it, I would rather not

I just picked up the bike and I am going over the thing so I can go ridding with my 15 year old son. I take it for a spin and she doesn't go past 5k rpm and the power is way down. I am thinking an air intake or exhaust problem. Bring it back to the garage and pull the muffler off. What a difference that made. Holy smokes. Ran great!

US model will have a removable insert with a small amount of packing wrapped around it.  That part is likely not clogged as the passage is big and can be repacked easily.  (Packing doesn't do much on that model)

The main part of the muffler has a "Krizman" design spark arrestor which has some vanes and passages to catch sparks.  That's what normally clogs.  There is ZERO packing in that part of the stock muffler.

Best way to clean is remove insert and heat the spark arrestor section red hot with a large torch or toss it in a campfire for a few hours to burn out the carbon.  Then dump out the ash, repaint, and reinstall insert.  

Alternatively, some people have reported taking the muffler to a radiator shop and having them use their cleaning tank to "boil out" the crud in the main muffler

Here's what i do. Works for me!!. Also have a good look or a poke down where the muffler engages into the chamber, they grow there too. If it's particularly bad then idealy the complete pipe needs a good burn out but see how you go & sounds like your muffler is the main problem.
photos.app.goo.gl/kCLdXfVLt9ooh7Sz9

Got it. Thanks! That was my original thought, but didn't know for sure. I will probably need to do the entire pipe. I doubt it has ever been cleaned.

Caution.  The main "expansion chamber" part of the pipe on that model is more or less "double wall".  Inner wall is perforated metal with a thin layer of fiberglass packing between it and the outer wall.  If you "burn it out" you will burn out the fiberglass and could end up with a louder bike and/or a rattle.  


You can inspect the head pipe and if a lot of deposits exist, that part isn't double wall and you could burn it out with a torch.  The exit pipe that connects to the muffler can also be inspected for heavy build up pretty easy with a flashlight.  

I would not burn the main pipe out unless it really looks like it needs it.  It's the spark arrestor/muffler that tends to clog on that model.  

Got it. Thanks so much for that tidbit of info

@MarkT,  how can I tell of "it really needs it"?
 
 running the bike without the spark arrestor or air filter (rode it on asphalt only), It will only go up to about 6000 rpm. Now I haven't done jack to the bike really, so I was going pull the carb and clean it (it is leaking fuel at the bowl anywau) install a new airfilter that isn't all rotted out, and add Boyesen Dual stage reeds. . Then ride it again without the spark arrestor and see what I get. Fuel is pre mixed at 40:1. 

 does this sound like a good plan of action to see if the expansion chamber needs cleaned? I am also performing an experiment with purple power. I plugged the inlet end of the park arrestor and filled it up with purple power. Every day I go out and agitate it. Looking pretty gummy in there, but lots o stuff is coming loose. Maybe I can try this on the expansion chamber?

also, there is quite a lot of oil coming out around the gasket between the cylinder and exhaust. . I have a new gasket on order. Could this excess oil be clogging up the pipe?

No magic potion poured in is going to clean out build up like this—just saying!!. Pic of my 100 twin pipe. photos.app.goo.gl/5vu4Pj6UyUUd8jSJA
Here’s a random google image I saved ages ago of a clean spark arrestor. If image is from someone on here then credit to them. photos.app.goo.gl/iF2tD8UXBx94MD5BA

You should be able to inspect the main pipe with a flashlight like I mentioned.  Especially the exit.  If there's a thick layer of hard carbon build up, then maybe but that's rare to find on the later bikes.  

It might sound kind of cheap but I have had good success removing carbon build up using "LA's Awesome" degreaser from the dollar store. I have used it for decades. 
I used it on engine parts from a neglected bronco I bought. Burned oil buildup from skipped oil changes left a thick layer of flaky carbon scale baked into the inside of the motor. I left parts soaking overnight in the awesome degreaser and the carbon came off of the areas that stayed submerged overnight. For a silencer of try putting it an a gallon ziplock bag, fill the bag with the Awesome degreaser and squeeze the air out of the bag before zipping it shut.
I have been surprised at what this cleaner can do. Sounds pretty cheap but for $1.50 it's worth a shot. Get the bigger bottle without the sprayer. 

Im a heavy equipment mechanic. Sometimes I get gobs of grease on my work uniforms I use the awesome degreaser to pre treat before washing with great success. I get my shirts and pants cleaner than the uniform service does using it. I also use it with a solvent brush to do most of my parts cleaning on my automotive and motorcycle projects. The stuff works Awesome.