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
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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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