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On 3 Nov 2002, at 17:04, Mark Seaton wrote: > I'm still trying to get to the bottom of my poor mpg performance (<20mp(uk)g > avge). > The thing is the engine seems to run really sweet. At its MOT test (which it > just passed with flying colours- but then both the testers have told me how > much they like it and one of them asked me if I was taking good care of his > car ! :-)) it read about 500ppm hydrocarbons on the emmissions test. He said > that was a bit high but nothing to worry about. What is the spec here? HCs would be high if it was running rich. > I have a '73 dual carb manual and as such the timing is 7.5 deg advanced. > I'm using cheap unleaded with a pump rating of around 95-7 Ron. Should I > increase the advance for the unleaded? When I have increased the advance at > idle while fiddling around, the engine speed increases. This is good isn't > it? Shouldn't I be trying to tune the engine for the best power (highest > speed ) for a given carb setting? When I bought it it was set to about 20deg > adv at idle. I thought perhaps the flywheel was on wrong but I just checked > that and TDC is TDC. You don't want to just turn the advance to get the max idle speed. That will give you much too much advance at speed. You SHOULD check the vacuum and mechanical advance mechanisms to make sure that they are BOTH working smoothly. The vacuum advances sometimes die and they are there to improve gas mileage. The mechanical advance mechanism often gets rusty and sticks, giving reduced power and awful gas mileage. > Also I just fitted a Pertronix Ignitor as a last ditched attempt (plus my > points were getting pitted regularly). When I checked with my crappy > rpm/dwell meter it read 60 deg dwell. Is that OK? I guess the coil will just > run cooler? Extra advance will actually make the coil run hotter, but that's with the std ignition. It may not make any difference at all to the Pertronics. In general, the dwell to shoot for is 45-50 deg. - ******************************* 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/