Dell'Orto VHSB and VHSH30 carb help (Includes Manuals)

I’m doing a clean of my carburettor for Rotax senior max and I’m trying to identify what these two particular screws are called. I keep hearing people referring to them in different names.
What’s A called

What’s B called

Is one like low and high speed idle adjustment?

1 Like

A is an idle speed screw which basically adjusts where the slide stops/how much it closes.
B is your idle mixture screw. It is an air screw, so screwing it in reduces the amount of air at idle… ie screwing it in richens the idle circuit.

Thank you for that. So now once I attempt to start it, what are the neutral positions for these screws? Should I screw them in completely?

Here’s some Dell’orto resources I’ve found over the years. Although not for the VHSB specifically, many of the operating principles apply…

JetTech Dellorto VHSB34 QD and QS Max manual.pdf n.b JetTech no longer exists, I think the owner passed away.
Dellorto Manual - From Dellorto.pdf
Dellorto Primer Tom Barth.pdf (RIP Tom)
Dellorto Quick Guide Tom Barth.pdf
Dellorto VHSH30_Manual Vortex ROK.pdf
Dellorto VSVH30 exploded view vhsh30bs.pdf

VHSH30 Throttle Opening Stages and Circuits


Start with four full turns out (from fully closed) on the idle screw “A” and 2 full turns on the air screw “B”. Play with the idle screw so that when cold the engine should idle around 2,500 rpm, when hot it may not idle at all without a little throttle (that is fine).


ok will try that thank you

This worked for me recently after cleaning the carb :ok_hand::+1:


So I’ve finally started it up. Is it normal for the wheels to spin quite quickly? (I’m doing it on a trolley)

Also there seems to be a lot of white smoke emitted from exhaust.

White smoke is common when whanging the kart on the stand.