Vm29 carburetor

What are the effects of drilling your slides holes in a VM carburetor

It would probably have about the same effect as drilling some holes in your seat pan.

Some aftermarket jet kits require drilling a tiny hole in each slide on cv carbs. My understanding is that it is to reduce fluttering when using really light springs over the diaphragms. The slides in cv carbs are not connected to the throttle, and they raise and lower based on air pressure.
VM carbs have mechanical slides, so there is no diaphragm spring. The slides are directly connected to the throttle, so the slides do exactly what the throttle does.

I've never heard of drilling holes in a mechanical slide carb slide. What is this all about?

I think it would depend on the location of the hole and the height of the slide. These are just my thoughts, as I've never done it, nor do I know of anyone who has.


For a cold engine it would interfere with the choke circuit. Too much air, resulting in a hard (lean) start. VM carbs are designed to start with the slide almost totally closed in order to create a rich mixture for starting and idling.

At warm idle it would allow more air through the venturi than normal, (and probably less fuel through the pilot jet) again causing a lean condition and possible over heating.

Above 1/4 throttle it probably wouldn't make much difference depending on the size of the hole relative to the size of the opening in the venturi. At full throttle I think it would make no difference because the hole would be drawn up above the venturi.

Is this assuming that the holes go all the way through the slides?

I hope the op will clarify what he is about.

TexasKZ wrote: Is this assuming that the holes go all the way through the slides?

I hope the op will clarify what he is about.

That was my assumption but you're right....the question needs clarification. Maybe he means a hole in the top where the needle sits??