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| Joined: | 09-17-2007 |
| Location: | San Francisco, California USA |
| Posts: | 221 |
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But once I got everything sorted with the cam, the primary problem was the transition, and I had the same coughing and sneezing. After installing an AFR meter I could see some aspects of the problem as being lean but it was still kind of inconclusive. I would richen things up but it would solve part of the transition, not the other conditions including WOT or idle or top end. It was also hard to tune off manifold vacuum because of the extremely high overlap Dave Bean DB9 cam I was running (even more overlap than a 104).
Everything changed when I started messing with the emulsion tube. Like magic, transition was achieved and the other issues then became about jetting and messing with the idle air jets, especially setting for max vacuum like Tim always suggests.
No expert here, but the observation is that the emulsion is kind of the "camshaft" of the carb. It seems to determines when primary and secondary happen. I've used this method now to tune a few non-standard built Porsche's, etc, even a old 289 Ford engine running 4x IDF's, and it seems to work as long as you get the choke and auxiliaries generally right.
But maybe this is more for high rpm and higher performance engines, not much experience tuning stock.
I remembering reading an interesting story years ago that a British manufacturer, maybe it was Bentley or Aston (pretty sure it was Aston) had secretly contracted with the Weber company to get one of every single emulsion tube they ever produced, and they keep a library of them still at their facility. Many emulsion tubes have been lost to history, and of course the racers were modifying their own. A black art indeed, but when I married my Dave Bean 2.0 built engine with the F3 (weber), it was a match made in heaven.