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On 7 Jan 2003 at 23:21, Mark Seaton wrote: > I'm wondering if the need for a higher pressure pump than T1s and buses is > to do with the fact that we (except the FIs and single carbs) have twin > carbs, and therefore 2 float chambers to fill when the needle valves open- > the effective pressure can be halved as its shared between 2 valves. It's the flow that gets split, not the pressure. > To keep the level in the carbs correct, in the right period of time, it > would therefore need to shift twice as much fuel when the valves opened > and would need more pressure. A dual carb 1600 uses only slightly more fuel than a single carb 1600, because the only difference is that there is SLIGHTLY less air flow resistance in the dual carb setup, so the dual carb car can suck just a bit more air. It's nothing close to a factor of 2. > I've been listening in on this one because I had the exact same problem at > the same time as Daniel- my oil level had risen noticeably soon after an oil > change. At the time of the oil change I had enriched the mixture on my carbs > by 1/2 turn. The engine was really running smooth with that change, but on > inspecting the plugs they were pretty sooty. They weren't that bad though. Here something I've been wondering about in this thread: Don't the mixture screws control JUST the idle mixture, while the main jet controls the mixture across the open throttle range? So I don't see how misadjusting the mixture screw could make much difference unless the engine spend all its time at idle. > I still have no idea why my engine should want to run so much smoother on > too rich a diet, but i've now got a hunch that we really do need the higher > pressure pump for optimum performance. They wouldn't have made it different > for nothing would they!? The higher pressure will certainly raise the fuel level in the float bowl somewhat, but someone will have to send me a carb before I can tell how much this might change: I suspect not much. Didn't someone suggest that the change might have been to compensate for the pressure drop in that special little valve some of these cars had--the one with the crossover connection between the intake and output lines from the pump. That's the best idea I've heard so far. If that's true, it would mean that the higher pressure was not needed if you have lost that crossover valve, which is common, I hear. -- ******************************* Jim Adney, jadney@vwtype3.org Madison, Wisconsin, USA ******************************* ------------------------------------------------ To unsubscribe, E-mail to: <type3-off@vwtype3.org> For more help, see http://vwtype3.org/list/