Dellorto DRLA 40 B. What jetting for a 2110cc Type 1 engine?

It's the other way round, the one per barrel are manifold vacuum for balancing but you are correct, he could use one for the distributor if he used a programmable distributor set to only react above idle rpm. I think he'd have to snip the inner end off the fitting or it would have to be loose to pass the signal which wouldn't be ideal.

 

I beg your pardon, you are right.

 

Cheers John
I didn't have air trumpets on when i was rolling roaded, they only came after i lost an air filter stud down the carb!
I know have 43mm air trumpets/velocity stacks.
I found a parts diagram for my exact model of carb DRLA B, it shows what looks like a vacuum union take off.
Got excited until I went and looked, I just have 4 manometer brass things that are for carb balancing apparently.
There is a metal recess (5) where it looks like a vacuum take off could be drilled if, but i was advised against doing this and really don't fancy it.

 

I have 4 brass 'sticky out bits'.
One of the ones on the left hand carb (towards front of bus/cylinder 3) looks like it has a black insert with a tiny hole in it.
The rest may have as well

 

Left hand carb

Have i got these right?
1. Manometer/carb balance? Why do parts diagrams label them as Vacuum take off union
2. Air Bleed screw?
3. Mixture screw?
4. Progression port blanking screw
5. Where a distributor vacuum take off would/should be

 

DRLA 40B parts diagram.
I have this same carb on both sides. My right one has been modified with a throttle stop welded on.

Seem to be a few minor differences to 'normal' 40 S (left)

 

5 is where you could drill out/pipe for a distributor vac take off.

 

5 is where a less cack handed skilled person could drill out/pipe for a distributor vac take off, if the carb owner wasn't fearful of it and worried about ruining them/leaks!

 

Get stuck in! Don’t use hammer action

 

Eurocarb's reply to my enquiry about vents & jet sizes. Hope they don't mind. I've removed their personal info.

Thank you for all the info - usually we offer the below specs based on engine size but the choice of main venturi size will impact where you power is.



The smaller your main venturi (chokes in the above table) the better your low end torque and response but the lower your max RPM. Given what you've said it sounds like you would get better performance out of the 30mm setting instead of the 32mm.

The air correctors can probably stay at 175, they are close enough and only really impact higher end running - but the idle jet, main jet and chokes will be the important items to consider.

The jets need to match the choke size so I would advise changing the jets if you alter the choke size. The above specs are general and unfortunately can't account for engine modification but for approximately 95% of setups it should run well.

Kind Regards,

Eurocarb

​

 

4. is a cover for progression ports
So Eurocarb agree 30 vent.
Be interesting to know if your distributor vac was drilled then plugged. If you had it in your hand you could look.

 

It has likely been drilled and plugged.

 

pic looks like a lead blanking plug possibly. If you did decide to go for a vac take off then possibly a carb specialist might be appropriate!

 

Just knock a nail into it

 

Push it out from the inside.

 

then of course you would need a tube inserting to connect the pipe to!

 

Thanks i'll update it.

Next time the carbs are off i'll have a look and see.
The external place where the distributor vacuum would go look factory sealed, so I assume you mean looking for the internal 'holes' like in your picture to see if they have been plugged?

Is your photo of the main carb body where the butter fly thing is, so only visible when the venturi and auxiliary choke bits have been removed?

 

It's looking from underneath, or rather the carb is upside down, you'd need to take the carb off.

 

Yes, that's what I meant. You still might not want to do it but it would be less stressful if you knew the drilling was there with a short lead plug.

 

Yes of course a specialist job, but well before doing anything like that id have to understand what actual benefit it would bring me.
I really don't understand vacuum advance/distributors etc.
I'm certainly not considering whacking a hole in my left carb at the mo!

The start of this was discovering I had 32 vents the other day and then asking if some jet changes may help with fuel economy.
If the entire carb and manifold can easily be be removed & refitted with the engine in place, then looking at the jets/vents is something i will consider (with someone local I know who has carb experience).

My concerns are no access hatch, bigish manifolds & not much room to get a spanner in, ease of re fitting manifolds back on without getting leaks etc