wcfvw69 wrote: ↑Tue Jun 05, 2018 6:38 pm
Timing 10deg ATDC @ 800-950rpm
Advance 7-12deg Adv
Retard 16-18deg
Centrifugal 21-25deg @ 3400 rpm
Here's the specs for that distributor. When it was run on my Sun distributor machine post restoration, the vacuum canister was right in spec on both the advance and retard. This spec sheet shows it should be timed at 10* ATDC which is unusual for the DVDA distributors that normally have their timing set at 5* ATDC.
Bill, it is not unusual. 5* ATDC was indeed to improve airflow through the central idling (and the Pict3 bypass Type 1 carburetors), yes. But the 10* specification was exclusive to the air-pump-equipped '73-'74 buses only.
It was the timing specification for
MY VW bus for thirty years! Thirty years of 10* ATDC. I have met it in many many many other factory dual carb buses, dhoch14, greenolivemedia, volksfolk74, satchmo, ChiTwnVW, Turk, needvwparts, Birdibus, cooperm81, iwantmybustorun, the list goes on.
wcfvw69 wrote: ↑Tue Jun 05, 2018 6:38 pm
I'm not sure what Bosch/VW had in mind for the retard to be so many degrees unless it was for smog passing purposes. It was the tough smog laws of 1973. Clearly VW installed this distributor/vacuum can when these where new back then and they ran fine.
I am sure what VW had in mind for the 10* retard specification. Remember the air pump? The air injection system with the air pump? It HAD to have damn good and hot exhaust for the injected air to burn off any remaining hydrocarbons. 10* retard at idle helped to make sure combustion was happening into the exhaust manifold as the exhaust valve opened. Many many many European cars, like my beloved Mercedes and BMWs of the 70's and my '77 Porsche 911 engine were also using air pumps with thermal reactors and they all needed retarded ignition timing at idle.
wcfvw69 wrote: ↑Tue Jun 05, 2018 6:38 pm
I think I suggested via email to Earl to yank that DVDA out and install the 009 as a quick test. Set the 009 timing to 7.5BTDC and see how the engine reacts to it. Condensers can act bizarre too, even new ones. If the 009 ran good, then he knows the condenser and distributor are ok.
Nope. We are not going on goose chases (get it, Earle, "goose chase"??). We are going to follow the diagnostic track set out and we will report back as we check off "what it is not", which is as, if not more, valuable as exploding possibilities of what it may be. I know condensors, even the new ones, and this is not that sort of hard ignition based cutting out.
So let's get back to the math and why I find so many older distributors with greater and greater centrifugal
range. We are absolutely committed to NOT exceeding 28* at sea level with a stock engine. Done. So why did my distributor, which we ran up on your machine, give me 445* the day after our visit? Why did I have to reduce the max centrifugal timing to 24-25* BTDC @ 3,400 rpm to bring my head temps back down to low 400s? Why is my idle timing at 850 rpm
now 3* After TDC?? I cannot answer this, Bill. We tried to figure out what might make a distributor get sloppy, we looked at weights and their action against the upper shaft/breaker lobe. We could not find a visible reason for my observations all across this country. Yet, I have to stand by my observations, and I have to live by them as I drive long hot highway headwinds. The BobD, when new, had a certifiable 7.5* BTDC idle timing, and the centrifugal went no further than 28*. Now it is at barely 2* BTDC idle to maintain that 28* max. Why? 10 point essay (we discussed one possibility and I offered it as a tip for your customers)
Maybe Earle and I can figure out a way to "shim" the retard stop on his distributor. I know the numbers. I know them. We need to narrow down the
range.
a) if we are committed to 28* BTDC centrifugal max, and HIS distributor has 22* centrifugal range, then the centrifugal idle timing would be 6* BTDC, right? And we would subtract the requisite 16* of retard for a retard timing at idle of 10* ATDC. Right? Not what we are getting. We have (chime in Earle) 16* ATDC AND a max of 28* allowed. I have to run! They are closing this joint out from under me!
Colin