Hi folks 1st post for me here. Anyways.... I took my 74 dt 125 for a ride last weekend... ran pretty awesome! The missus and I are planning a trip to the holly oaks orv park this weekend. I checked out the rules and they're pretty specific on noise regulations. 94 dB max. I downloaded a dB app and revved up its at 100 dB. It still has the factory pipe, silencer and insert I do believe. Can I repack this to get the ol girl quieter or am I just pretty screwed on going? It's a 3 hour trip there just to get turned away. Thoughts?

Do you have the factory air box - air filter installed?  A lot of noise can come from intake.

If you do and have exhaust insert I'd be suspicious of the app accuracy, dB scale (measured using "a" scale?), and/or test method (distance and RPM)

A real 100 dBa is pretty loud.  I doubt a stock DT125 would be that loud 20" from muffler at about 3500 rpm?

Might be worth trying other apps (find one with dBa scale) or getting a real sound meter from Amazon?

Mark is right, those dB apps don't work very well. I did a bunch of work to make my motorhome generator quieter, and I was using one, and it seemed way off. I downloaded another app and it was about 10 to 12 points different. They also rely on your phone mic, which is not high quality.

Then I bought a meter from amazon for about $30 and got much more realistic results, and they were lower.

Does it still have the built in spark arrestor down deep in the tail muffler. Be pretty noisy without that, plus i guess its compulsory for forest riding in the US. Welcome too--i see you're new--enjoy.

Also, they should be measuring sound at a 45 degree angle from muffler...  not directly behind it.  That's the standard method anyway.

(When I was stadium racing we used to have to be under 99 dBa, 20" from muffler at 45 degrees...  it wasn't that hard to meet and engines were pretty darn loud.  Not sure we always revved up as high as we should have though (half redline) )

I found this:
 

Here: www.advrider.com/motorcycle-noise-limits-in-the-usa-and-canada/

So a 1974 DT125A sold in California met the 86 dB standard in stock form.They were the same in all 50 states.

Their procedure says test at half the rated RPM:

www.oakgov.com/parks/parksandtrails/holl...k/Pages/default.aspx

 

How much did you rev your 125?

Nice data on sound levels!

My 76 Husky came with a CHP approved add-on Skyway spark arrestor/muffler kit to qualify for a California Green Sticker..  Max allowable it had to meet was 101 db and it was LOUD. 

Good point on spark arrestor!

My experience at off-road parks is they almost always check every bike at entrance for a spark arrestor with the "rod test".  It's rare to see them do a sound test...  what normally happens is if a Ranger thinks bike is too loud when you're riding around they do a sound test away from other bikes.  That's in California though.  Where you are if might be different.  (Rangers in California love to see the old vintage bikes out riding...  we never got hassled)