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On 16 Oct 2003 at 14:07, Mark Seaton wrote: > I'm trying to get to the bottom of things with my engines less than expected > performance. > I wrote before that I thought the vac can might be faulty as with it > connected, the advance seems to advance too quickly on acceleration- in fact > it seems to jump up to about 25 deg advance at about 1500-2000 rpm which > doesn't sound right. With the can disconnected the progression is much more > even, though the takeoff from idle is far less stable and wants to stall. If your dist has both vac and mech advance, then the vac advance should only be active while cruising. > I removed the dizzy last weekend and took out the advance plate to look at > the centrifugal bits. It all looked OK and free but I did notice that the 2 > springs that attach to the weights are different. One has a longer loop at > one end so that it doesn't contact the weights' post at rest. It looks like > it is designed to come into action at higher rpms. So I guess this goes out > to Jim as he rebuilds these all the time- does that sound correct? This is correct. If you look at the dist advance curves in the Bentley manual, you will see that several of the curves rise, plateau, rise some more, and then stop. The plateau in the middle occurs when the weights hit the end of the long loop. Additional advance pauses until the preload in the spring can be overcome, and then continues at a lesser slope, because you're now fighting both springs. > Also Jim you said many times before that you shouldn't notice a difference > with the car at rest if the vacuum is connected or not- well I most > definately do! I guess that this could be something wrong with the vac > take-off on the carbs but I'm pretty sure that it didn't behave like that > always, and I've examined the carbs time and time again in comparison to the > original carbs and the vac circuit seems identical. The only thing I can > think of is that something is leaking and affecting the settings since I > removed/replaced the carbs after the rebuild. The throttle response seems a > bit sluggish particularly when you take your foot off- its slow to come back > down- could that be an indication of something wrong? I'd start by disconnecting the vac advance hose and seeing if it seems better that way. If so, then this is your only problem, and, yes, it is a problem. I'm not a carb expert, so I'm hard pressed to guess why this suddenly started to happen. When you get vacuum from this port depends completely on where the drilling enters the throat of the carb with respect to the throttle plate. I suspect that there isn't much difference between the 2 (at least) styles. It could be just 5mm. This port is in the throttle body, isn't it? Have you changed throttle bodies? If so, consider changing back, but I don't know if you can mix and match throttle bodies and carb bodies (are they even separate parts???) I could be wrong, but I don't think there would be any kind of leak which could do this unless you have a crack in a casting somewhere. > I'm getting a bit worried about this as at startup it sounds like it could > be pinking a bit which won't do my new pistons any good at all :-( Just disconnect the vacuum hose for now. See if that helps. On your dist, the vac adv is just there to improve fuel economy while cruising (high speed, low load.) -- ******************************* Jim Adney, jadney@vwtype3.org Madison, Wisconsin, USA ******************************* ~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~ List info at http://www.vwtype3.org/list | mailto:gregm@vwtype3.org