Tuning the Weber DGV for the L-Series 510 motor
So what can you do on your own? Well, you could buy a box of spiffy jets and other hardware, then spend about 100 years trying all the combinations to find the ultimate results. This is done commonly and is generally called racing. Or you could listen to what others have done with similar applications and buy a much smaller box of spiffy jets and things and probably achieve the same results. Or you could go to someone who has already done this enough times to know how and is willing to do it for you. In the end, you will have a simple little carburetor that performs great and that you understand a bit better.
The good news is that the Webers, as you buy them, are set up very close to what you need. (Caution: if you are the junkyard dog insisting that the $10 DFV off the old Renault you found is right for you, you have your work cut out for you, I promise. I intend to try to save you some of the joy of that tuning exercise here.) This data is for rather mild, more or less stock-type motors. If you really want some unique, high-power motor, you probably aren't going to use the DGV anyway. You may elect to challenge my advice and, if you add to it, I'll be pleased. What I just promised is to lay out a tuning procedure using the small box of spiffy jets. To begin, you must have a solid engine and fully functional electrical system. It sounds silly, but most of the time a carburetor is replaced because another part is malfunctioning. If the engine isn't pumping the air in and out smoothly and predictably, then the carburetor hasn't much chance to match that air with gas. If the electrical system isn't firing all of the cylinders properly, tuning the carburetor will be no help. I find that, most of the time, my first evaluation of whether a problem is carburetor or ignition is exactly wrong! The point is to first get the simple stuff right.
We are now ready to start in on tuning the carburetor. Take the top off the carburetor and locate all of the jets, the nice brass parts. They are brass so they can be easily produced with the required precision, but you can easily mess them up with the wrong size tools. (The correct tools for this job were covered in the previous article, which also has cutaway drawings to help you locate and identify the parts.) Write down their values and put them back in exactly the same place from which they came. Few will fit into the wrong location, but be very careful and thorough here. The top is held on with six screws and a clip on the choke linkage. Use the proper sizes of screwdrivers and take your time. You may be able to buy all the little pieces for a Weber but you'll not like their cost!
The idle jets are in holders on both sides at the top of the body. The air jets are in the center on the top, the e-tubes are directly beneath them in the body, and the main jets and power valve are in the bottom of the float chamber. The accelerator-pump jet is the little aluminum wing-shaped part overhanging both halves of the carburetor. The float valve and float are in the top cover. Generally, you won't change the power valve unless it is damaged. It's located on the very bottom of the float-chamber floor. You should now have a list of jets something like: primary idle 60, primary main 140, primary air 170, primary e-tube F50, secondary idle 60, secondary main 135, secondary air 170, secondary E-tube F 52, and pump jet 40. Measure the float height from the top by holding the cover vertically with the pivot at the top and the float dangling and just closing the valve. If you just measure it upside down, the distance will be too small. It should be 41mm with a brass float or 35mm with a plastic float.
Reassemble everything and test the performance of the car. Make note of any popping or surging and where they occur as the throttle position and load changes. Write things down and take your time. Try to imagine where you are in the range of flow I rambled on about a little while ago. The trick is to go right to the area of concern instead of the one next to it. It isn't easy but it can be fun. It is typical for this carburetor to have richness in the primary progression. This offers good power characteristics but is overdone for our application (The DAF is just the opposite). You will feel it as a hesitation at light load, and you may have a black tailpipe after a freeway cruise. This may not be as much a problem on a two-liter as a 1600. Also, it is typical for the secondary to have a lean progression which will feel like a hesitation as you open the secondary and maybe even cause a pop back through the carburetor. You should be able to feel the resistance of the secondary as you open it with the throttle at about 2/3 travel. Finally, look for a hesitation when you suddenly add throttle at several points along the flow range. The accelerator pump is usually a bit small, and this is a good indication. Lean will feel like a sudden loss, whereas rich feels like a gradual one, and right on feels very good.
