Those who were at Stretton knew this would come up sometime!
For those who weren't, I took the opportunity to borrow the decibel meter from the circuit, not because they were bothered, or for any other reason but to have some background feelings/numbers to have.
Certainly some of our karts are loud, but for other venues there are noise limits, as much for the sake of keeping their neighbours not objecting as any other reasons. If we are to make approaches to other places then I would hate for anybody to be sent away.
Likewise, I had already ordered an exhaust of the type many are using, and was keen to know if that would be over any limit. Clearly it would be, and from the numbers gained might be substantially so. The loudest with a GX type pipe was over 115 at 2 metres, and that is way over the limit, some places 105 within 1 metre, and other places lower still.
Well the results are in, and for almost all that were at Stretton, a venue I am in discussion with would be off the list with the current levels of your cars. In fact only one would be allowed! Take a bow Chris.
Of course the question is what can we do. For those who have purchased from the GX Tuning store, they have a muffler designed to go with the pipes purchased. Will that bring the noise below the limits at some venues? Sorry I have no idea, but I don't want to approach property owners if I don't have confidence we won't annoy them. (Or their neighbours so we can't go back.)

I used one of these on the Morgan: https://www.ebay.co.uk/itm/Exhaust-Pipe-Muffler-Universal-Fits-for-50-150cc-Dirt-Bike-Sliencer/192870106095?hash=item2ce7f443ef:g:RvMAAOSwOZNcmKVB. Even without a baffle, and with a blow at the head I got a maximum reading of 80Db at roughly 1m. I know a phone app is not particularly accurate, but good enough for a go / no go check.

With the prospect of actual meetings at sites that have noise restrictions in place, it's time to be measuring your noise levels, and if necessary making changes.

As an example, Curborough has a limit of 105 dB measured 0.5m from the exhaust at 45degrees from the axis of the exhaust,  this is at 2/3 max revs.

There's a few smart phone apps that will measure sound levels for you.   They are seldom as accurate as dedicated meters, particularly at the higher sound levels, but will give a good indication.   If you are keen, the meters aren't too expensive.

This table compares the sound levels from a few different exhaust set-ups.   It's from an article that describes how to free up the airflow in a standard GX200 silencer/muffler.

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Source: http://affordablegokarts.com/pages/modify-stock-muffler