To All:
I'm building a 94x69 stump-puller for a splittie van. Weber 32/36 DFEV. Alternator, full-flow oil filtration, pre-lumber and points-triggered CD ignition module. CR of 7.7:1 Pretty much a Plain Vanilla truck engine except for the balancing and HVX mods.
Lower end is no sweat, goes together nice after nailing down the valve train geometry. Mantling is chore because all the tin-ware -- real VW stuff -- needs to be re-worked. Finally get the fan back from the balancer and and start doing the final chores, one of which is setting-up the manifold for the Weber progressive, a task I've done a time or two (and written about).
Back in the Day, the aluminum casting on the Weber kit was a disaster. Sand cast, you had to spend a lot of time cleaning the core residue out of the manifold & heat-riser. Not this time. Casting was a beautiful lost-foam jobbie; the interior of the plenum required neither cleaning nor smoothing.
Neither did the heat-riser bore. Because it wasn't there (!!)
Oh, it was drilled on each end... for about 1.7" But since the casting is 6" long the remaining two and a half inches of solid aluminum was liable to reduce the flow just a tad. As in, zero-tad.
It's a waste of time trying to sending junk like this back -- you'll spend more for attorney's fees than it's worth. Instead, you can cost them a hundred times that simply by steering business to other retailers.
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So how do you open it up?
Drill it out. Regular jobber-length drills won't work because of the manifold tubing sticking out, four and three-eighths out one side, six and three-quarters out the other. But aircraft drills come in lengths up to 18" and I just happened to have some. Kinda big -- you need to open it up to half an inch -- but if you start out with a small-diameter bit (I used 7/32") from either end and go just half way, then open that up to a full quarter-inch, a regular half-inch drill bit fitted to an extension-shaft will give you a clean, on-center cut.
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Vaporization of gasoline is endothermic. Flat engine, center-mounted carb, long intake runners, you need a LOT of manifold heat. Simple physics.
Once you have someplace for the heat-riser gases to flow THROUGH you need a place for them to flow TO, such as the low pressure area immediately adjacent to the tail pipe, which is how the stock VW muffler is designed. (Good engineering) By comparison, the typical after-market exhaust system only provides access to the exhaust stacks at cylinders 3 and 4, which means you end up trying to push gas from one high-pressure area to ANOTHER high-pressure area... which don't work. And neither does your Weber progressive because of that simple fact.
Single-barrel carb, stoichemistry is typically too rich at low rpms and too lean up high. Only place it runs really good is near the middle of the range, which works out to about 37mph for a 1600cc engine in a bug. Run at that speed here in California, it'll get you a ticket for obstructing traffic :-) Progressive carbs take care of that by providing a much broader stoichiometric band, allowing you to cruise more econmically at a higher speed... assuming the thing is properly installed. Which it usually isn't, in the case of veedubs. But there it is :-)
-Bob Hoover