dellorto 40/45/48 carbs question

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dellorto 40/45/48 carbs question

Postby jamezz666 » Wed Sep 02, 2020 3:42 pm

Hello Everyone

So i bought a pair of Dellortos on a 2.3 manifold and the story goes... the carbs was stripped rebuilt but sleeved to a different size.
i've taken a picture of where the ID number should be and as you can see, they look to of had the 2nd number burr'd away and by the looks of the carbs they've had some work done, as they have new gaskets/bolts/filters/ ect.

my question to the people who know there stuff on dellorto's / webers.. what the bloody hell have i bought :lol: ?

I measured the end where the throttle flaps are and the ID come out at 48mm as pictured, i measured the other end which i think is called the venturi and the ID come out at 45mm and i measured the manifold and the ID was 45mm and i tried to do a rough internal measurement at the narrowest point and that came out roughly 43/44mm

could these of originally been 40's bored out to 48's? i did a bit of google research and found the odd couple threads, of people mentioning boring out 40's to 46's, so it must be they've been bored :?:

Any help will be much appreciated! bare in mind these was purchased with the intention of fitting to my 2.3 GT which the only other mod will be a 4-2-1 manifold

Pictures below

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Re: dellorto 40/45/48 carbs question

Postby droopsnoot » Wed Sep 02, 2020 6:09 pm

There are two things here. The 48mm (or 45, or 40) refers to the bore size, which is what you have measured at the flange end. Inside that, you have the choke, which can be different sizes, matched to the requirements of the vehicle. Obviously, the choice of carb (40/45/48) limits the maximum size of choke that can be fitted.

I believe that normally the chokes have their size on them, but the ones on my Firenza don't seem to have as far as I can see, and it's visible from the air filter end, not the end you have shown. While I have a spare pair of 48s, they're on a manifold so I can't take all the same measurements that you have taken. The fact that the number in the casting has been removed suggests they have been altered in some way. I haven't heard of Dellortos being modified in that way, but then I haven't been researching it either.

This is the back end of mine, last time they were off the manifold. I had a similar issue to one that looks like has been fixed on yours - the blanking plug on the rear gasket face sits a few mm below the rest of the casting, so it was letting air in. Not sure the photo helps at all, other than to make me jealous of how clean yours are.

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Re: dellorto 40/45/48 carbs question

Postby 1972nail » Wed Sep 02, 2020 7:03 pm

The measurement at the front is the ID of the auxiliary venturi. Behind it is the main Venturi. The aux vent is held in by a grub screw with locking nut shown in my photo. Slacken that off and the aux vent should slide out followed by the main vent.



The main Venturi usually has a number on the front, here's mine showing 38 which is the correct size for a mildly tuned 2300.



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Re: dellorto 40/45/48 carbs question

Postby jamezz666 » Thu Sep 10, 2020 12:19 pm

Thank you for the information guys.

I took the choke out and there was no numbers as pictured above on the inside of it, so i decided to measure it up and it appears to be 45mm and then i measure the body and it comes out at 48mm. So i'm guessing someone bored them out to 48's.

So for a 2.3 engine with just a 4 branch manifold on it, would it pay to get hold of some 38mm chokes to put in? what else would i need to change? or would the guys at a rolling road change all them parts?

sorry for all the questions, this will be the 2nd time having a pair of carbs like these

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Re: dellorto 40/45/48 carbs question

Postby droopsnoot » Thu Sep 10, 2020 12:29 pm

The Sportpart manual talks about using DHLA 48s for ultimate performance and talks about 41mm chokes for a rally engine when fitted with a performance head and other mods. Unfortunately it doesn't talk at all about using them on an otherwise-standard engine.

I was about to ask whether it's even possible to get 38mm chokes for a 48mm carb, but someone does list them. I'm not sure how they can be for "Dellorto 45/48" unless they get confirmation of which further into the order process.

Not sure whether the rolling-road people will have these parts ready to swap - I imagine that will depend on which company you use. I've never been on a rolling road and have wondered whether it would be down to me to source various carb components that they'd need in order to set things up properly.

If your only other mod is an exhaust manifold, aren't these a bit over the top even with smaller chokes? It won't run as smoothly as it does on Strombergs, and it'll be a pig to idle when it's cold.
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Re: dellorto 40/45/48 carbs question

Postby 1972nail » Thu Sep 10, 2020 6:29 pm

The bit you are measuring is the auxiliary choke. The choke is further in. You can see it in your other photo near the butterfly. It looks like it is a bit smaller than the bore.

Idle and main jets, air correctors and emulsion tubes are becoming rarer for these carbs and fewer rolling roads keep a wide stock to try and test for best performance.

Certainly for a standard or mildly modified engine 38 mm chokes are the way to go but the ones you have there do look as if they may be OK.
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