RM400 restrictors in expansion chamber

[Fabulous]

Ok so my mate pulls the pipe of his 79 rm400 and it sounds like someone has left a screwdriver inside. Cuts it open to reveal a metal plate with a 30mm hole and a say 150mm perforated pipe welded to it( this had broken off, that would be the noise then.) This is all in the pipe, NOT the muffler.
Havent come across this before. Was this stock on these?. Anyway, it is all cut out and welded back up ready for sandblasting etc. Is there backpressure issues?
Thanks in advance.

[zorroz]

This was standard issue back then to tame them down I believe? I done the same thing to mine pulled it out went like a rocket.

[JohnnyO]

Yep that was standard for the 400n/t models

[Short Stuff]

I had the same issue with my PE250.  Big, ugly restrictor in the chamber.  I cut it out.

It didn't go before.....it hammers now!

[lukeb1961]

I had the same issue with my PE250.  Big, ugly restrictor in the chamber.  I cut it out.

It didn't go before.....it hammers now!

The PE had that to shut the thing up. You know, the reason people hate dirt bikes and want to see all tracks and trails closed?
Removing the restrictor is fine - so long as you put a decent muffler on. My farm was next to the local cop. I quickly put a healthy big muffler onto the bike. Went fine and didn't upset the ah.. neighbours.

[Short Stuff]

The PE had that to shut the thing up. You know, the reason people hate dirt bikes and want to see all tracks and trails closed?

Mmmm..I'm aware of that.  Spent a fair bit of time with AMTRA and Roger from the DSE spreading the "More Ground, Less Sound" message.

Removing the restrictor appeared to make little difference to the sound of the bike.  What did help, was replacing the baffle (that came with the bike), with a NOS one.  One of my next projects is to try and make a perforated screen insert for the muffler, which I can wrap in wool to try and quieten it down a bit more.  It's not bad now, but as you say, if it can be quieter (without affecting the way the pipe works), then that's a good thing.

[Lozza]

Inserting the stinger back into the pipe is one of the most effective ways of deducing dB levels, just facing the silencer outlet toward the ground helps as well.