How to reduce exhaust noise level back to specification of 78 dB

Insizwa

CB750 New member
Messages
1
Reaction score
0
Points
1
Location
H3110hello
Hi Guys, I have a 1976 750 K5 that I am trying to register (in Portugal). The exhaust noise test results came in at 98bB at 4000 rpm whereas the original registration papers have the acceptable level at 78 dB. Is there a way I can temporarily or permanently reduce this for a follow up test? The bike has stock pipes with small diffusers at the end. Thanks in advance for your help. Grant
 
That year had the multi chambered non-serviceable HM341 pipes and the end is more of a trim cap than a diffuser, so they're either drilled out or rotted inside. Maybe pull the ends out and pack the final chamber loosely with baffle material? The end caps/diffusers should keep everything in place for the dB test.
 
Last edited:
Where was the bike originally registered to have an acceptable noise level on the original documentation? I've never seen this before, in the UK exhausts must have a BS or Euro approval mark but unless the bike is really loud I don't think too much notice is taken.

Loki
 
Back
Top