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Date:         Mon, 02 Oct 95 11:07:27 PDT
Sender:       Vanagon Mailing List <vanagon@vanagon.com>
From:         Nick Pace <nickpace@rand.org>
Subject:      VW-'71 BUS-1600 DP-DISTRIBUTOR ADVANCE CURVES-QUESTION

I know this has been hashed over time and time again but I have to get something straight in my head and soon. I have a '71 VW Bus with a newly rebuilt stock 1600 dual port engine. At idle, everything checks out just fine but going up hills and throughout all phases of acceleration something is just not "right". It's just a hint of hesitation that perhaps is all in my head (while my van was down for a month, I drove a friend's econobox and got used to zippy little cars). I don't seem to have any vacuum leaks (though I haven't checked all the way to the brake servo), I made sure the carb jets are clean (a 34PICT3), valves are adjusted AOK, plugs are new and gapped, etc., etc., but there is a feeling that I don't like. On the other hand, while I've been driving a 1600 Bus for 25 years, I occasionally get paranoid about performance even if there is nothing wrong. Additionally, I just put in a rebuilt long block so this might be a function of the breaking in process or something is funky with the rebuild (though I now have about 400 miles on it and it should have worked itself out by now).

Anyway, I eliminated most of the easy stuff and now want to check the distributor. I have a "stock" dist with vacuum advance & retard. I say "stock" since I think it is really from a 73ish bug based on the way the condensor mounts on it. Most importantly, it passes the California smog inspection so I haven't messed with it. Unfortunately, I couldn't read the serial numbers this morning before writing this novel since it they face forward. What I am wondering now about is whether I'm getting the right advance at high RPMs. I checked the shop manual and it gives the advance curves for centrifugal and vacuum distributors at various points. Unfortunately, the vacuum distributors like mine are rated in terms of mm Hg. rather than RPM. When I did my long block, I put on one of those cool and shiny crankshaft pullys, stock size, with the degrees marked all the way around. I'm assuming that I can check the advance using a normal timing light (without one of those dial-in features) simply by opening the throttle and seeing where the pully lines up with the timing mark on the crankcase.

Anyway, in the back of my mind, I remembered that 27 degrees advance at 3 grand RPM was about right (I know that is not exactly correct but it's the right order of magnitude). The manual figures for most of the centrifugal distributors show **about** 9 to 14 degrees advance at 1600 and 21 to degrees advance at 3400. When I checked my distributor I got these numbers (yes, I know that the idle settings are not exactly up to specs but it shouldn't affect the higher RPM settings):

RPM TIMING DWELL 850 2 ATDC 51 1500 24 BTDC 50 2000 32 BTDC 48 2500 36 BTDC 47 3000 44 BTDC 46

Do the timing advance figures seem high to you? What should they be for a vacuum advance & retard distributor? If they are wrong, could they be the source of the subtly wrong feelings I get when zipping along?

As always, thanks for any advice,

Nick

------------- Nicholas Michael Pace RAND 1700 Main St., Santa Monica, CA 90407 Nick_Pace@rand.org voice:310-393-0411 ext. 6176 fax:310-393-4818


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