Dellorto DRLA 40 Carburretors, Jetting and turbo application.

22nd August 2009

I had always used Weber carburettors in the past and was always hearing that Dellorto carburettors were far superior from people who had used them for years. With my new engine now progressed to the long block, I had to decide how I would supply fuel to it. Previously I had a project that consisted of a Garret turbo T3 unit and a drag exhaust that had been extended to work together. None of this had made it onto an engine and I figure that with the new strong block that I had built this would be the best time to bring it all together. With this in mind I new I could not use Weber carburettors as they could not easily be modded for turbo use. I found two Dellorto DRLA40 carburettors online in an auction that originally were from an Alfasud. I new the jetting would be wrong for the 1600 long block, but I figured that the jetting would all change with the turbo anyway so this would not be a problem. The first thing I had to do was to thoroughly clean the DRLA40's up. This is a fairly large job as it does not just entail cleaning the outside of the carburettors . The inside must be stripped down and cleaned thoroughly too. I decided this was the way I was going as I knew that ultrasonic carburettor cleaning techniques although good, would not find broken or missing parts should there be any. Once the carburettors had been thoroughly de-greased with Gunk, I started to dismantle them. The filter covers are bolted to the top of the carburettors, with this removed the top of the carburettors can be seen and access is then available to remove the top screws that hold the two parts of the carburetor together. It is beneficial as well to photograph the components before removing them so that you can easily remember were they go when rebuilding. The top will then come off the carburetor and will take with it the float which is attached to the roof of the carburetor.

I contacted John Maher Racing Ltd ; Mr John Maher in the Outer Hebrides, The isle of Harris. http://www.johnmaherracing.co.uk to ask him if he still could machine the pair of DRLA carburettors for turbo spindle seals. He told me that he still had the equipment to do this but he also said that he could not covert all Dellorto carburettors. He went on to say that you needed a 20mm boss inside the middle of the carburetor to give enough room to take the turbo seals.

He indicated that he had seen carburettors in the past that did not have this and could not be converted. Luckily my carburettors were OK and I sent them of to him. You can see the boss on the inside of the carburettor wall clearly. the picture also shows that unlike the outer bearing which is sealed. the throttle shaft runs straight onto the crab bodywork meaning that the surfaces had no seals to keep fuel in the carburettors under more than atmospheric pressure. The carburettors throttle shafts have to be routed out with a special tool that allows one side of the carburettor body to be done at a time. The picture right show the process of cutting the turbo seals. This is repeated three times for each side as three steps must be cut into the body to allow a plastic washer, o-ring and star washer to be fitted. The whole process is done from the outside of the carburetor with a cutting tool mounted on a spindle that is passed through the existing throttle shaft-hole. The cutter is also supported on the shoulder of the other side of the shaft. Some cutters have a cutting surface on each side. This actually allows the process to be simplified by pushing in and pulling out to do each of the bosses. It is imperative the recesses that are cut true to the throttle shaft .

The picture left shows the machined boss ready to take the turbo washers. It shows the three cuts made into the sidewall of the carburetor. I used the specialist services of John Mayer as I felt that he had the tools to do the job correctly. Obviously this is a risky modification to a carburetor as if the seal leaked then your whole engine could go up in flames very quickly. I ordered my turbo seal kit from Euro Carb http://www.dellorto.com and waited for my carburettors to be returned to me.

My carburettors came back very quickly and I was very happy with the machine work that had been done. I previously had stripped out everything but the throttle body as I wanted to keep the machine costs down. I knew I just had to rebuild the carburettors and had taken some good photographs of the carburettors in various states of being dismantled. The first job was to fit the new turbo seals into the newly machined areas. This seemed at first an easy job as it required fitting the washer and the o-ring followed by the star washer which was pressed into the recess to hold the washer and o-ring in place. My first attempts at this resulted in the star washer pinging back out. I decided that I would use the throttle spindle to line up the washer and o-ring so that the star washer could be pressed into place. I also used a small pair of pliers around the spindle to press the star washer from opposing sides. My patience was soon rewarded and I manged to get the four seals in place and the throttle spindle back in the carburettor with the ball race seal at each end. It is very important when assembling the throttle to match the spindle to the right carburettor side, as the spindle protrudes more on one side to accommodate the levers for the linkage system.

The butterflies could then be fixed to the throttle spindle again paying attention to the way they came out. It is important to put these in carefully as they will not fit if forced and they are very easy to bend. The rest of the carburettors could then be built up . The accelerator pumps were renewed and fitted back in. The other ancillary items where added to the carburettor and all the components where cleaned and assembled as can be seen photograph left:


At this point I had to decide what I was going to do about jetting. Fortunately I had met a gentleman Dan on Volkszone who had turboed his Beetle . He suggested that I should start off with the jetting he had as the cars had a similar specification as he had had his carburettors professionally set up. I bought the turbo conversion kits as they came with the turbo gasket and the high capacity needle valve for the float bowl.



DRLA 40 Aspirated jetting
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• 4x Venturis 28mm
• 4 x Main Jets  1.20
• 4 x Air corrector  1.8
• 4 x Idle jets 7644  .6
• 2 x Pump Jet 0.35
• 2 x Needle Inlet 1.5
• 2x starter emulsion tubes 7482.3
• 2x Starter Jet 60
• 4 x Emulsion tube 7212.2

DRLA 40 Turbo jetting
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• 4 x Main Jets 160
• 4 x Idle Jets 7644.60
• 4 x DRLA Pump Jet 10927 not DHLA 10927.
• 4 x Turbo Emulsion tubes 9164.turbo
• 2x starter emulsion tubes 7482.3
• 2 x starter jet 3315.80
• 2 x Air Corrector (short) 7482.170

This was quite a shopping list as the jets and emulsion tubes are only available from a few outlets. Luckily I found some CB Emulsion tubes on eBay that were better than the standard ones. I also found main jets , Idle jets an air corrector from a dealer on eBay: Fast RoadCars. The rest I would have to buy from Euro Carb. It is important to note that some parts can be shared between the DHLA and the DRLA with jets . The exception to this though is the pump jets 10927 which the DRLA uses longer versions than the DHLA.

I was very surprised how expensive the jets and the turbo conversion had cost. In hind sight It would have been cheaper to have bought one already modified but then I don't think I have seen many on the market for sale as in recent times there has been a drive towards efficiency and the carburettor has been surpassed by the injection system. This said the injection system is a whole lot more complicated and I was intending to cut my teeth on a turbo system that had a smaller number of parts to go wrong.

If you are considering doing this conversion to a set of carburettors budget at least £80-£100 for the DRLA 40 carburettors, the machining will cost upwards of £69.00 depending on how they are delivered to JMR, Turbo Conversion gaskets, seals, pump valves and other ancillaries around £96.00 without the re-jetting costs which if you may be able to source the parts from other suppliers.

I would have to purchase a new CB linkage kit for the carburettors as I knew that the CB pressure covers only fitted the CB linkage kit.

Prices current 2009 only.