Ever since my stock Bosch Dual Vacuum Dual Advance distributor (DVDA) failed last year I’ve been looking for a replacement. The problem is they don’t make them anymore so most people use the commonly available new Single Vacuum Dual Advance versions. The Mexican Bosch SVDA is my favorite, I run one with a Pertronix ignition in my other bus, very nice. The DVDA has two vacuum hoses that are fed from the stock twin Solex carburetors. If you run the SVDA you’ll be blocking off the retard vacuum hole on the left carb. I’m a bit of a stickler when it comes to running things stock so I’ve kept my hopes up to find something in the way of a DVDA that is close to my original. I know the literature says that you should run distributors recommended for your particular engine and year, but if that were true no one would be running 009s or the aftermarket SVDAs, the latter made for Mexican Beetles if I’m right.
Out of the five DVDAs I now have, including my broken original, only one is working to my satisfaction. I’ve been to a few shows and events this summer and whenever I see one I buy it. Prices range from 10 to 20 dollars and condition from rough to usable. They’re inexpensive, which means I can afford to be wrong here and there and keep the bad ones for parts. The most recent one turned out to be rated for a ’75 – mid ’76 Bus with an 1800 to 2000cc engine, and since I have a ’73 1700 I feel it’s about as close as I’m going to get. I took it apart down to the springs and weights which looked quite good. At first the advance plate didn’t want to come out, however a little persuasion in the vice with a gentle tap from a center punch convinced it to come free. I degreased, cleaned and lubricated the whole works and added a set of gently used Bosch points and condenser.
Now came the moment of truth, I installed said DVDA into the bus, set the static timing at 10 degrees After Top Dead Center (ATDC,) made sure it was out of gear and started it up. It ran at low idle, I adjusted to 900 RPMs or there about and set the timing with a strobe light. By the way, the dwell read 44 degrees, nice. Took the van for a spin, but it seemed a bit sluggish, went around the block straight home and checked the static timing. Went out again, same thing, not quite right. I had noticed I wasn’t getting enough advance when revved, could the vacuum can be finished? I decided to give it one more try. I reset the static timing, then got out the strobe light again. This time it was reading nearly 10 degrees out at around 20 ATDC, weird. At least I had found something to fix. I reset everything to specs and headed out for a test drive. What a difference! It was running like its sewing machine self. I think the trick is to get the idle as close to the recommended 900 RPMs then check and recheck your 10 degrees ATDC setting. I hope this stock set up with the twin Solex carbs will improve my gas mileage a bit.
One thing I should point out. The old green retard vacuum hose began to crumble and rip when I went to connect it back up. The gauge looked a lot like a 5 mm fuel line hose so I grabbed some of that out of the spares box. It seemed to fit perfectly and is functioning just fine, perhaps they are one and the same type of hose.