Hello, I wonder if anyone can help please? My son has a rev 3 125 2006 with the dellorto VHST 26 carb. I have taken the carb out to clean it and check jets, it has a threaded hole here which leads straight into the carb bore, should this be blanked off? I can't believe it's right to let unfiltered air straight into the engine?! Also does anyone know the standard jets/needle position for the dellorto? Thank you.

I'm used to the PHBL, but your VHST looks like this photo: https://www.speed-parts.nl/carburateur-dellorto-vhst-26-mm-bd-flat-slide.html

The casting probably was made that way so it could have mixture and idle screws on either side.  You could test with compressed air.

 

 

Yes, I agree it looks like the casting is made for both. It definitely goes from outside to inside, I thought the unused side would be blocked or capped. I wondered if anyone had the 125 and could confirm or deny?

5 hours ago, reghusky said:

I thought the unused side would be blocked or capped.

Typically, the unused side would not have been machined.  If it was like that from Day-1, the engine would have had a massive air leak and never worked properly.

Yep, that's what I think Konrad, I wonder if it was meant to have a blanking plug in it which has fell out. It was running but idle was erratic. Piston, rings and crank seals have all been done.

I don't see that you have anything to lose by plugging a hole that should not exist.  Personally, I would try something quick and dirty like hot-melt glue.  If that was successful, I'd use epoxy.

That's a good idea, I was wondering what to plug the hole with! Cheers.

Reghusky, I’d suggest you use an epoxy putty to fill the hole. It’s very easy to control the application. You simply cut off the amount you need and mix it with your fingers. If you use a 5 minute liquid epoxy it could run inside your carburetor and make problems worse. I inserted a link to JB Weld SteelStik that’s worked great for me and it’s formulated to work on metals. You could use the leftover to put in your toolkit in case you break something while on the trail.

The other option, if you can determine the thread, is to put a screw/bolt in the hole then tighten it down. That way it can be removed easily in the future.

https://www.jbweld.com/product/steelstik-epoxy-putty-stick?srsltid=AfmBOoow4TSrJyoiKEz1T--jEoSYMv0MvMKrvs4AjsApeWY9MXnM8HpG

Edited October 14, 2025Oct 14 by RonH

As konrad said they are like that .This is for when the carb is used OEM on a bike that will have the adjusters on the left hand side e.g early GasGas pro 280 There is no need to plug it it is already blank , it does not matter if dirt gets in the hole ,  it will not get inside the carburettor.

Thanks everyone for the help, I checked inside the left-hand idle hole and it looks like a small black cap has blanked it off, I suspect the mixture hole had one too, I've temporarily hot melted glue in there and it's running much better, idle is perfect now! Just gotta find carb jets base level now. Thanks again, I now have a very happy son!