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While waiting for the Grandkids to arrive for Christmas, I found this in my “new” book How to Hot Rod Volkswagen Engines book. I thought that it was particularly interesting since most of us are aware of the #3 cylinder running hot and many run the Bosch aftermarket (centrifugal only) advance distributer. I changed from the Bosch almost immediately after buying my TD due to stumbling, not overheating. But read:“Don’t be surprised when you run one of these (aftermarket) distributors on a distributor machine and find that one of the cylinders fires 2 degrees (distributor) retarded. Because these distributors were designed specifically for the VW-type engine, the #3 cylinder fires 4 crankshaft degrees later than the other cylinders to temperature compensate it for its tendency to run hotter. It runs hotter because the stock oil cooler blocks air to that cylinder. This is the reason why the service manuals make such a big point of insisting that you time the engine onb #1 cylinder with the distributor in a specific position to fire #1 cylinder. It is also why you should install the spark plug cables correctly in the distributor cap exactly as they come from Wolfsburd. You cannot wire the distributor in just any position even though you use the correct firing order – regardless of your past experience with other cars.”I’ve got to admit that my past experience caused me to wonder why they make such a point of distributor position. I ignored it since, – “I knew better.”
….and who knew that the distributor was designed to fire #3 late? Certainly not me, with all my experience! 😮 “Experience is what you get just after you need it”In a related note:If you are running a 34-pict-3 carb. and a centrifugal advance distributer, you’ll notice a “dead spot” when trying to accellerate. A 34-pict-3 is designed for use with a vaccum advanced distributer and the carb sucks too much air with its side vaccum port “capped off” creating a lean mixture until the centrifugal dissy can catch up to adjust the timing.To alieveiate this problem (short of replacing the dissy) is to remove the carb, take off the bottom throttle plate and brazzing over the 1/8 inch hole in the plate. (the hole provides the extra vaccum for the vaccum advance).You will also need to advance your timimg slightly to compensate for the centrifugal “delay” on accelleration. Do NOT advance it too far!!! It will run like a raped ape, but will burn up the pictons!!!Another problem (especially with kit cars) is that the stock VW oil bath air cleaner is replaced with a filter breather. This increases the amount of air introduced into the air/fuel mixture, and decreases power. these babies were designed to breath thru oil!Hope this helpsSTG-inc.2012-12-25 13:12:53
Thanks for the help, but, I really don’t have a problem. I went back to stock vacuum only immediately upon purchasing my TD. My post was to tell those who might be interested that the VW factory distributor cam is not asymmetrical and allows #3 to intentionally fire late. My guess is that none of the aftermarket distributors do this.
Royal2012-12-25 15:06:05Sorry… I miss read the meaning of the post. When I read “Stumbling”, I assumed you had the issue I spoke of above… Oops!
No problem.
I bought the book because I have been contemplating dual carbs. Fisher, the author, says that a single double barrel carb would be better than duals. It is a mute point anyway because I just discovered that I do not have the clearances required for dual carbs under my engine cover. I’m still trying to get smart on these single port engines. Trying to find a single port manifold with a Holley Bug Spray now.I can tell that you are one who’s posts I will be watching carefully – I love learning.Roy – I wonder that since VW moved to the “Doghouse ” oil cooler if they went back and reset the timing for No. 3 cylinder. Does it mention that in your book?
Doug – I’ve always used the oil bath filters. On my Ghia I used a 36HP oil bath filter on each carb and plan on doing the same with my 34PICT3 carb with the butterfly hole brazed. They come up fairly frequently on eBay and cleaned up and painted they look great.Allen Caron
VW based 53MGTD - "MoneyPenny"
"If one thing matters, everything matters" - from the book The ShackAllen,
It would seem logical that they would have taken the fudge factor out of #3 lobe on the dist cam if the engine has a doghouse cooler. But, I have seen no mention of it. Yet. I just got the book this morning and am doing a quick read through. Then I will do a study through (which takes longer) over the next couple of days. I happened across this fact which caught my eye.I suppose if you had a degree wheel, you could see a 4 degree retard on #3 at idle, since the retard is mechanical and fixed at 4 degrees throughout the rpm range. Set the timing and without changing anything else, move the timing light pickup to #3. If I run across any more words of wisdom in the book, I’ll try and pass them along.So far, this seems like a good book with lots of do’s and don’ts and alternative suggestions on how to accomplish whatever it is you are wanting to do.. My book is the version which covers all engines through 1971. I also have Bentley, Chiltons, Haynes, Purvis and Muir. There is very little that I have not found in Rob and Daves VW pages here on the internet, and that plus Muir’ Idiot book and perhaps this Fisher book should be required reading.Let me apologize to all you old VW types who know all this stuff. I had been away from VW’s for more than 40 years, have just come back and this stuff is “new” to me. The Fisher book has been around for 40 years, so this is certainly not new.Royal2012-12-25 18:14:22
For my engine builds I use Tom Wilson’s “How to Rebuild Your Volkswagen Air Cooled Engine”; 1987 edition.
Allen Caron
VW based 53MGTD - "MoneyPenny"
"If one thing matters, everything matters" - from the book The ShackI heard that number 3 retard story and believed it. As I have the old single relief, case, single port heads and the old school fan shroud I’m guessing I should have that timing quirk–but don’t know if I do. I am running a vaccuum dizzy with a 34 PICT 3 carb. And it’s not quite right. Pops a little on decel during normal operation and cracks like a rifle shot if I floor it and then get off it.
Ed, I just KNOW that you have checked all this out: http://www.vw-resource.com/backfiring.html. An exhaust leak (after you have set timing, valves, carbs) is most likely. You and I likely have the same engine and could only disprove that by taking your jugs off. I’m now a 1600cc on an old single port Hxxxx engine since earlier this year . Don’t I remember that you run Pertronix ignition? If so, then I doubt that your #3 is retarded. (but I could be wrong on that)
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