[Date Prev][Date Next][Thread Prev][Thread Next][Date Index][Thread Index] [New Search]
On 31 Aug 2003 at 19:48, Craig Webb wrote: > Hello all, been lurking in the background for a while, whilst slowly > rebuilding my 72 Square. Finally got it to the road-going stage and now > have a question about timing. > > I have the dual vacuum type distributor on my dual carb engine (probably not > the 1972 original). The distributor number is 311 905 205T. > > I've tried to confirm the timing settings for this distributor without much > luck. I found one reference which said 5 degrees ATDC and another that > suggests 7.5 degrees BTDC. With such a wide range of options, I'd like a > third opinion please! The vacuum adv/retard + mech adv dists are quite different in their tuneup procedures from the more "normal" dists with vacuum and mechanical advance. The thing to keep in mind is that the retard is applied only at idle by a drilling that produces vacuum ONLY when the throttle valve is completely closed. The first thing to do when you have one of these is to make sure that the vac retard is working properly. Check the vac retard by watching the timing marks with the timing light to verify that the timing marks JUMP to the left as soon as you open the throttle a tiny bit. If they don't, either that vacuum port is blocked, or the retard side of the vac can is damaged. Unfortunately, the latter is commonly the case. I say unfortunately, because these dual adv/retard cans are EXPENSIVE. I don't have a listing for the 205T dist, but I MAY have your vac can if it is the same one that the FI uses. I can tell if you can give me the 3 digit number off the actuating arm of your can. If your retard is working, then the usual timing for these is 5 deg advanced, with the retard hose disconnected. You can also connect the adv hose, but it should do nothing until you're actually on the road. I think you'll find that when you time it like this the timing will jump to approx 5 deg retarded as soon as you connect the retard hose. You will have to readjust the idle speed between these two measurements because timing it at 5BTDC will make it speed up and you don't want to time it with the mech advance coming into play. So keep the idle speed below 950 RPM while doing this. Once you have that part working, make sure that the more important mech advance is also working. This is easy to verify either by twisting the rotor and letting it snap back, or by watching with the timing light for smooth advance and recovery. > I looked on www.oldvolkshome.com/ which has an excellent listing of just > about every bosch distributor except mine. I suspect it's biased towards > the USA and doesn't cover the UK. Can anyone help me out with a definite > answer for this distributor? See Dave Hall's site. > I'm timing it dynamically at idle with both hoses on at present. That's not the correct way to set these distributors. VW really wanted you to set the timing to the spec that it would jump to as soon as you give it a little gas. We mimic this condition by removing the retard hose. The advance hose should have no effect at this time. If it does, then you've got something hooked up wrong. -- ******************************* Jim Adney, jadney@vwtype3.org Madison, Wisconsin, USA ******************************* ~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~ List info at http://www.vwtype3.org/list | mailto:gregm@vwtype3.org