Hey there trail busters, just a silly question really.  On a standard carb, piston, head, reeds, air filter etc are they successful known 'tweaks' to the DT125 mono air cooled, as I just realised the PO had made 2 small 'extra' holes at the bottom of the rubber snorkel, I suppose to get just a pinch more air ,  (and the bike is running just great with this config) have there been known working tweaks that dont require heavy rejetting and so on, I'm going to do a small run without the snorkel to see if that makes too much air coming in and I'll post a pic of the small mod done by PO, just thought it was interesting

Looks like a place for dirt to get in and wreck and an engine.
It’s been said before, Yamaha engineers knew what they were doing… way better than most garage wrenchers. I’d replace that before a ride.
Better performance can be done by changing jets in the carb.

In the USA, the 1978 DT175 had that tube on the air filter inlet.  In 1979 Yamaha. themselves removed it.  www.partzilla.com/catalog/yamaha/motorcy...79/dt175f/air-filter  The 78-79 DT125 both had it.

Most of the bikes I've seen here no longer have the tube so you should be fine without it.  Not sure if you'll have to re-jet without it, possibly a larger main jet?  But it will probably be fine as it was not uncommon to add extra holes to the airbox itself without jetting changes from what I've seen on a couple of 78-79 DT175's I've owned

Cheers Mark that's interesting. Like Sneezles says you wouldnt want leaves and whatnot getting in there, i'm suprised Yam didnt make a little grill to go over the aperture, which is what I may do if the bike runs better without it, otherwise its just going to go right back on!

Looks like the mice have been nibbling at it--like were nibbling at my muffler.
photos.app.goo.gl/bwpwVgLGNmnyv1wc8

Agh, that's kind of gooey, like something from Alien

And the new improved snorkel, definitely crisper all round ( I wouldn't have a clue as to it getting too lean, so I will ride with this version for now)

Wow that's restricting it a lot if that's the only way in for the air.
If it goes better now, then i'm thinking it must've been way too lean before.

Like I said before, Yamaha themselves left off the snorkel tube on the 79 DT175 and then redesigned the entire airbox for much better airflow on the 1980 models. 

It's a very tiny air inlet and very restrictive system even without the snorkel tube which in my opinion was used to help with reducing intake noise. 

Inlet also up under the seat and parallel to the ground...  very well protected from debris like "leaves".  

Snorkel tube does make a good "mouse block" though...  I think RT325 was right and the "modification" to the holes in the tube was likely rodent nibbling during long term storage.