[Date Prev][Date Next][Thread Prev][Thread Next][Date Index][Thread Index] [New Search]
On 3 Sep 2006 at 18:22, Steven Ayres wrote: > The cutoff jets serve a different function, keeping fuel from flowing > from the carb into the head when the key is off. Yes, but they are only part of the idle circuit. The engine will continue to run just fine if you disconnect them, as long as you don't let it slow down. ;-) > The antisiphon valve keeps fuel from flowing back toward the tank all > the time. I think you've got this part backwards. The siphon problem had to do with an occasional car where the float valves didn't shut off perfectly. In that case, the slight pressure from the tank, if on an uphill or with a full tank, could overfill a carb bowl and then trickle down the throat of the carb. If the intake valve was slightly open, or just didn't seal perfectly, then the cylinder could fill up with gas. The next time the engine was cranked, the gas would be incompressible and the engine would be locked up and possibly damaged. The late model pumps include a valve which doesn't let fuel move toward the engine unless there is a slight bit of excess pressure indicating that the pump is actually pumping. I don't know how the early little unit worked inside, but my understanding was that its job was the same. The only one I've ever seen was 30 years ago, and that one was covered with red RTV. There would be no tendency for fuel to move backwards (toward the tank) because there are already 2 valves, in series, in the pump which prevent flow in this direction. The thing I don't understand, is why didn't VW just increase the spring tension on one of those valves; the effect would have been the same with no increase in the parts count, no change in the other pump parts, and would have been easily retrofittable to any earlier car. -- ******************************* Jim Adney, jadney@vwtype3.org Madison, Wisconsin, USA ******************************* ~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~ List info at http://www.vwtype3.org/list | mailto:gregm@vwtype3.org ~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~