Vacuum leak at carb/intake adapter

[JLT]

This may help somebody else out at some point.

I have a 1600 DP with a Brosol carb. It attaches to the intake manifold via an adapter which steps the throat size down. On my last road trip, I started hearing a howling which was most prominent when the RPMs were low, and got softer when I applied power. I also noticed that my ability to idle had pretty much disappeared. My first thought was that it was the distributor going wonky, but when I replaced it with my backup distributor, the problem remained. I drove home thinking "Clutch throw-out bearing? Gland nut needle bearing?"

It turned out that the carburetor was getting a vacuum leak at the adapter. Tightening down the 13mm bolts didn't do a damn thing, because the adapter screws onto the carb with 6mm socket screws which you can't access until you remove the carburetor. I ended up removing the carb, tightening the screws (and adding a little thread-lock), and remounting the carb using new gaskets on both sides of the adapter. Problem went away.

The mechanic at Kombi Haus (where I had the Brosol installed in the first place) diagnosed the problem in five seconds flat by listening to the howl and then rocking the carb back and forth on the intake manifold. By the fact the he nailed it so fast, I'd suspect that he'd seen that problem before. So if you're using a similar set-up, be advised.

I should add that they didn't charge me anything for the diagnosis, and even gave me the replacement gaskets for free.