IDF Venturi Outside Diameter

[mr scoops]

I've been led to believe that the Venturi's on 36 and 40 IDF carbs can sometimes have the same outer dia, and other 36's have a diferent OD.

Does anyone know the actual dimensions?

I think one is 40.8mm, but struggling to find the other dimension.

I just want to know what figures I'm looking for when I measure mine later on.

 

[K@rlos]

If your shopping for vents then go into Eurocarbs website, go to IDF parts and scroll down to 36 IDF Venturi’s. 28mm & 30mm are the only sizes available for those carbs so just pick the size you require.

To me it seems like your over complicating things tbh....

 

[mr scoops]

I have spoken to Eurocarb today.

They asked me what OD venturi do I need?

'Some' 36's share the same choke dia as 40's
The other 36's do not, and are a different size.
They have asked me to measure the venturi in there currently to confirm. I have managed to find out that 'some' are 40.8mm OD, I'm trying to find the other dia, basically so I know if I can measure with a steel rule or if it's really close I need to borrow a vernier.


Don't see how that's me complicating things?

 

[K@rlos]

That’s new 1 too me, I’ve owned and dealt with dozens of 36’s and never came across that :shock: use a decent ruler, you’ll soon see if they are closer to 40 or 36. In which case if your reads 40. Something Mm then that suggests you need the bigger set.

 

[sparkywig]

I have spoken to Eurocarb today.

They asked me what OD venture do I need?

'Some' 36's share the same choke dia as 40's
The other 36's do not, and are a different size.
They have asked me to measure the venturi in there currently to confirm. I have managed to find out that 'some' are 40.8mm OD, I'm trying to find the other dia, basically so I know if I can measure with a steel rule or if it's really close I need to borrow a vernier.


Don't see how that's me complicating things?

Did you tell Eurocarb that they're off an Alfa Romeo? Did you give them the numbers (if any) stamped on the carb body?
Have you checked the inside of the venturis for diameter stamps?
My Italian IDF40s came off an Alfasud and are different to Spanish carbs and had earlier pump jets, but all the venturis were stamped with the diameter.
You'll need a vernier caliper to measure them as the difference is in 10ths of mm.
Take the existing venturis out and measure those.

 

[mr scoops]

There's 0.1mm difference in them. I've taken one carb off and looked at the jets etc that are in there.

Eurocarb advises the following.
Vents: 28
Idle: 60
Main: 145
Air: 165
Emulsion: F11

I have:
Vents: 30
Idle: 52
Main: 135
Air: 155
Emulsion: F47

I was going to stick with the venturis, but change the rest.
As you know, the engine is a 1641 with Engle 100.

 

[atafonso]

The vents should be chosen according to your intake valve size. Normally 3-5mm smaller than the valve for a more performance oriented engine, so if you have stock valve heads and drive mostly in the higher rpm range, i would leave the 30's. If you use the Bus in town a lot and do not rev high all the time, i would put the 28's because a 1641 with a W100 can be a bit soggy in the bottom end
Abel

 

[mr scoops]

28’s it is then. I’ll measure up.
Thanks

 

[mr scoops]

A trip to the garage before work this morning and I whipped the top off the carb I'd removed last night.
Pretty sure the Venturi OD is 40.9 although I'm tempted to buy both sets and send back the ones I don't use for a refund.

Glad I've looked in the carbs though, float bowls had metal particles in! Will give them a good flush out!

 

[mr scoops]

Ordered both sizes, I can send back the 'other' vents then.
Who knows, Cinders may yet go to the ball!

 

[K@rlos]

Basically the smaller vent will give you better bottom end drive ability. And with a 100 & stock heads it’s clearly not intended to be an 8000 rpm screamer

 

[mr scoops]

Agreed.
It transpires that the vents I have are the larger 40.9mm dia, so I have a nice shiny set of 28s going in there.