Seeing the "sleeper" pip thread made me wonder what is inside a stock pipe, and is there anything that can be done to improve them without having to cut them open.

I assume that internally there will be some baffliing, and fiberglass wadding or simiilar. I was suprised that when I gently tap the pipe on the 400 it sounds very solid - could it be clagged up?

I was going to give it the caustic soda treatment to clear out some on the clag, but burning it out seems to be another way.

Then there is the spark arrestor - sure I have seen someplace that knocking out the baffle that is in there helps with performance.

The syatem on my DT is in remarkably good condition so I dont really want to destroy it, but if there are things I can do to get a little more performance out of the bike it would be good.

Just about every 2 stroke I have had over the years I have ended up fitting expansion chambers to.
 

Wouldn't do any harm to clean it out, although obviously take great care if using caustic soda.

Might only be US bikes that had the spark arrestor and I'd expect to see details of it (and the manufacturer?) stamped on the tail pipe.

Mine is a US Spec model.
The arrestor is stamped:
YAM-KRIZMAN Spark Arrester
Model KS-350

So is this spark arrester an arrester and silencer?

"So is this spark arrester an arrester and silencer?"

Over to our US friends!

Hi Andi,
here pictures from inside the muffler and silencer of my DT 250B. (German Bike VIN Code starts 512 instead 450)
The muffler should be the same as in US.
The silencer is different to US because no spark arrestor. The whole unit is welded together from factory side.
I guess for Sleeper rebuild the back section (Picture #4) is opened and a cone is welded in.
But thats secret of Dave Meis, i could lhave a look inside my Sleeper No 106 by Endoscope but i would not reveal.
     
 

Thanks for the pictures - as oy say the exhaust as per pictures 1 to 3 is probably the same on my 400, the mesh looking stuff on the inside I guess is there to absorb heat and noise ?

No idea what is in the end piece (the spark arrestor) apart from the removable baffle which has fibreglass wadding wrapped around it.

Perhaps one our US buddys might be able to shed more light.

I am loathed to do anything to it as I know how sensitive 2Ts are to exhaust systems - might just give mine a dose of caustic soda to clear out any crud and leave well alone.

I'd like to see the results of caustic compared to burning out but i guess it depends on how hard its burnt or strength of soaking. I used caustic back in my BSA days with boiling water & crankcase halves in a big bucket. The cases fizzed & bubbled & looked great like sooty black magnesium, but oversized the crank bearing holes haha. Wouldn't affect your pipe though.

You learnt the hard waay that Caustic Soda and Aluminium Alloy dot mix then !

Think some BSA Bantams had an alloy end cap on their exhausts which caustic would make short work of.

I think that burning out would probably do the best job, when using caustic I usually pour the solution in the pipe and leave overnight.

US Forest requires a spark arrestor. Look up Krizman, much better than a clogged screen seen on chainsaws.

cliff

Cliff - are you Cliff that posts on the KTOG site? Guessing that you are from your Avatar.

I get it about the spark arrester, just not clear whether the one fitted to my DT doubles up as a sliencer and spark arrestor, I am guesisng that it does.

I also find it surprising that the DT exhaust contains no cones or anything else - it seems to be just an empty chamber, so different to Kawasaki Triple exhausts.

I have a lot to learn about these bikes so apologise if I keep asking dumb questions.