hey anyone here know much about the late model 84-03 australian dt175 i have heard these are restriced im looking into possibly dereistricting mine to get a  bit more power.... first thing i have noticied is the stupid small exit hole from the muffler/silincer anyone bored this out bigger? already has no restricting ring in the header pipe thanks

Two strokes need a certain amount of backpressure in the exhaust or it kills the power.  Too much backpressure will make them run rich and can overheat the piston crown.  Not sure what you consider "ridiculously small" but in my opinion it's not likely that Yamaha restricted the muffler outlet.

What I remember seeing is people with those models claiming the main body of the pipe contained baffles that they removed..  not sure that helped or just BS.   (I removed the plate inside a US DT175 pipe, ton of work, LOST power)

So it might be best to research the facts first...  the air cooled 175 had roughly 18 HP which isn't a lot by modern standards.  It doesn't make sense that Yamaha would "restrict" a bike unless they had a good reason. Like in some countries they had HP or top speed restrictions for a beginners license class or something.  Or the registration fees were very expensive over a certain HP rating. 

The AG bikes that were designed to plonk along at low speeds and Yamaha built it that way, which is what they do..  Why would Yamaha build a powerful bike and then purposely restrict it? (except possibly for a "legal" reason stated above).

Which is all a long way of saying don't blindly believe "Internet lore" and hacking the muffler or whatever might hurt performance, not help it.    (That said, a good aftermarket exhaust almost always helps...  with the trade off that most are much louder than stock which might not be allowed where you live.)


 

I remember one year DT175 had a flat end on the muffler with a ring of holes around the edge. Not a very exiting looking muffler.
Best idea in my mind would be to burn out the exhaust & muffler so ya starting from a clean system.
"burning them out" & BURNING THEM OUT are two different things, so just be as sure as you can that its clean & in no-way restricted somewhere.
Air box inlet might be over baffled & restrictive to stop inlet noise.
All these emission rules make for restricted power.
We got probably the same models in NZ here as you in Oz.