Jetting Delorto DRLA 40 Twin Carburettors

3rd Feb 2012
My 40mm/28mm chokes had turned up from Italy and I was very pleased to see that when they arrived they were in fact the correct parts I had ordered. I had been previously trying to cure the jetting problems of my carburetors where my engine was idling well but had a lack of acceleration that could be resolved by pumping the throttle. I had believed that this was because of the size of my idle and main jets but had been told by both VW Heritage and Dellorto UK that it was more likely that my chokes being 40mm/32mm where the wrong size for my engine and was likely to be the cause of the jetting issues.

To fit the chokes into the DRLA40 carburetors is a fairly straight forward procedure, First the cross bar linkage needs to be removed . This is best achieved by unscrewing one of the ball ends that attach to the carburetor linkage plates. This has the result in making the bar shorter in length and able to be removed. The connecting rods then need to be removed from the carburetors so that it can be pulled out. You can carefully pull the bar out of the way to gain access which is the route took. To change the chokes you need to disassemble both Carburetors, it is usually safer to do this one at a time and rebuild so as not to muddle up parts. The Dellorto DRLA 40 carburetor is built up from the top . This means first the linkage bar plate needed to be removed by the four screws that held it in place. After this has been removed a gasket can be easily removed from the top of the Carburetor to expose the four inlayed bolts that hold the top of the carburetor on. Great care should be excorsied as the top plate holds the gasket and the float assembly . When separating the top from the body of the carburetor ensure that the gasket does not get trapped. It is sometimes easier in tight positions to remove the fuel line first.

With the top removed the DRLA 40 Auxiliary venturi can be removed . These are held in with two screws and a clocking nut at the front and back of the carburetor. Pictured right the screw hole with the top positioned on the carburetor . Once the nut has been loosened a screw driver can be used to undo and remove the bolt once these have been withdrawn the Auxiliary venturi pictured right can be removed. It is important to notice that the Auxilary venturi are handed and have different opposing sides . When re inserting the Auxillary venturi you must ensure the face with the o ring is positioned towards the centre of the carburetor otherwise the acceleration fuel jet will not be able to work correctly. When you have removed the Auxiliary venturi the chokes may be withdrawn from the carburetor twin barrels.


The barrels of the carburettor should look similar to the picture left. You should check the throats of both barrels are clean with a lint cloth. The 40mm/28mm chokes can then be lightly lubricated and placed back in the carburetor one in each barrel with the size stamp facing upper most . Once these have been seated . You can place the Auxiliary venturi back in the to throat above the choke it is important to ensure the rubber o ring on one side of the venturi is facing towards the main jets. With both venturi in place the securing screws can be re inserted and tightened to hold the venturi in place . It can bee seen that if teh screw does not hold the venturi tightly then the venturi is reversed and will need to be removed and fitted correctly with the o ring towards the main jets.The locking nuts can then be placed on the venturi securing screws and tightened. The top of the carburetor can then be refitted ensuring that the gasket is trapped correctly between the two parts. This can be a fiddle as there is a little spring that sits on top of the choke unit that can interfere with the refitting process. Once the top is positioned it can be re bolted back together with the four bolts. The gasket can then be placed back on top and the linkage plate can then be positioned on top with the washers , spring washers and nuts. The Air Cleaner can be re fitted and the other carburetor can then be attended to in the same way.

The linkage kit can be fitted into the linkage plate on one side and the ball joint tightened to remove any play.

Current DRLA 40 jets
Chokes 40mm/28mm Ventri
Main 112
AC 180
Emulsiontube 9164.4
Idle 60
Pumps 35

I was unable to test my new installation as I discovered that my Starter motor had failed.