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Vaccuum Diz Q's (long)

I've been reading alot about the advantages of the vacuum advance and decided to experiment. Found in storage my brothers old diz out of his 68.

113 905 205T single vac single advance. put it in my eng, 1600 dp, with a Brazilian 30 pict 3 bought in 88 or so. Ran it for about a week now, all seems ok, maybe a little more bottom end oomph than the 009 but hard to quantify. The problem is I get alot of popping and backfire type noises going downhill at say 40 in third gear or 25 or so in 2nd. I took it to a local used parts place looking for maybe a dual vac dual advance (70's type) diz, to trade a 09 and this 68 for, and seek advice. they wanted 75$ for a dvda, too much! I realize I'm trying to get by on the cheap, I just don't know how much difference the svda's at air-cooled.net at 100$ or so will make a difference. The 009 is "good enough" like my cooling tin without flaps is "good enough", my 30mm carb adapted to a 34mm manifold is "good enough". buying used tires is "good enough". My question is what may be causing this backfiring type noise? keep in mind this doesn't happen with the 009, so its not exhaust leaks or other probs. does the svsa retard the spark too fast when the throttle is let off? does it not ? thanks for any and all answers, I enjoy the group and all who post.
Reply to
Cletus
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How did you time the 205T?

Using a timing light, does the spark seem stable or does it jump around?

Max

Reply to
Max Welton

BTW, you can look up the specifications of your distributor at

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Max

Reply to
Max Welton

Reply to
Cletus

yea i've read that page alot looking for specs

Reply to
Cletus

In general, I think you're barking up the wrong tree. A vacuum advance has to be very carefully chosen to work with the carb you have. Mech advances are pretty much carb independent.

The dual vacuum advance carbs generally had a mechanical advance, a vacuum advance and a vacuum retard. They really don't work at all except in the stock applications, unless you have just the right carb AND don't connect the vac retard.

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----------------------------------------------- Jim Adney snipped-for-privacy@vwtype3.org Madison, WI 53711 USA

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Reply to
Jim Adney

Popping on decel under load is retarded spark. Did you leave the dist clamp loose? How well does the shaft spin. An old dist out of the junk box may be gummed up, and the engine is trying to spin the dist to retard. If the shaft is tight, pull the spring on the bottom of the shaft, push out the pin, remove and clean the shaft, and tube. Oil with motor oil, make sure the oiler hole in the side of the tube is clean, re-assemble and test. pin under the spring on the bottom

Reply to
Michael Kelly

I think the correct setting for single vacuum single advance would be

7,5 degrees BTDC. Timing to TDC will have it too retarded when=20 no throttle idle and revs high.
Reply to
Olli Lammi

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