Easily enough. Water vapor discharge is at its highest when the engine is
warming up. Most cars produce so much water vapor that it condenses in the
exhaust and is blown out the tailpipe during the warm-up period as liquid water.
If that combines with carbon deposits and/or oil deposits already built up in
the exhaust, it will produce a blackish liquid discharge. Given that you have a
fresh motor and than most fresh motors tend to burn a bit of oil until the rings
fully seat, I'd lay odds there is an oil buildup in your exhaust and that that
with perhaps a bit of carbon (which is normal in an exhaust) is combining with
the water discharge to produce your black liquid discharge. Mind you, I am
making no claims as to the mixture of your carbs. They may well be too rich, at
least at one or more rpm ranges and/or phases of operation (BTW, it is possible
to have carbs set up so they are both rich *and* lean, depending on the rpm and
operating phase), and that could be the cause of additional carbon deposits
which would then mix with the normal water discharge to make a black liquid
discharge. However neither that black liquid discharge, nor the mileage can be
used to determine if, where, and when your carbs are running rich. And you need
to know that in order to be able to make adjustments to the mixture. Otherwise
you are like a blind man with heavy gloves on trying to find a microdot. It can
be done, but it's going to involve a lot of luck and time. Most folks give up in
disgust long before they ever get there, which is why so many people end up
being unhappy with their sidedraft conversions on most cars. 2000 owners get a
big help from the fact that the factory spent a bunch of time sorting out the
2000 Solex setup. Even though the specific jetting from that setup may not be
spot on for most modified Roadsters, it gets them close enough they can usually
make the car run well enough.
As for Ron's question about a process for tuning the timing. Yes there is a
process. Due to the relationship between mixture and timing, you may need to
repeat the process after you do any carb rejetting. The procedure lets you
determine the maximum advance under full load that your engine can stand at all
rpms from idle to red line. Because it is determining when the engine will ping,
the mixture, temperature, load, and other factors come into play. Therefore you
want to ensure that there are no pre-existing problems that will mess up the
readings. For example, a clogged or inadequate radiator will cause the head to
run hotter and that will alter the point at which the engine starts to ping. So
you need to sort out all the problems that might affect the results first. You
also need to perform the test with the engine at operating temp and with the
type of gas you plan to use. Even the type of oil you use may have an effect.
BTW this is the sort of thing engine dynos are most often used for, the process
is slightly different on an engine dyno, but this is one of the things they do
to optimize an engine on a dyno. Engine dynos are much better suited for this
sort of thing than they are for comparing one engine to another.
Here's the way it goes. First remove the distributor and tear it apart. Replace
any worn parts and ensure it is in tip top shape. Next lock the mechanical
advance and the vacuum advance mechanisms down so they are at minimum (where
they rest when the engine is not running) and can not move at all (this needs to
be done well as you will be reinstalling the distributor this way and running it
up to red line repeatedly, you do not want things to blow apart while you are
doing this). Then you powertime the distributor at 500 rpm increments. (This is
where this process gets scary for most, you need to find a way to load the
engine so that it is running steadily at a given rpm at WOT, obviously a chassis
dyno would be best but this can get to be expensive, however most DIY
alternatives are pretty scary). Powertiming is a process of setting the timing
to the maximum it can be set to without any indication of pinging under heavy
load (or with just the slightest pinging under abnormally heavy load). You load
the engine so that it can just hold its speed at WOT, then you advance the
timing until you hear pinging, then you back it off until the pinging goes away
(I usually back it off another degree just to be safe). Do this every 500 rpm
from idle to redline and plot the rpm and timing as you go so that you build up
a maximum advance curve. Then have your distributor advance recurved to match
the plot. Now go test it in the real world and note any time you hear pinging.
If there are times, you will need to check the mixture at that point to ensure
that a transitory lean condition is not causing the pinging, if the mixture is
okay then you have to recurve the distributor or dial back the initial advance
until the pinging goes away.
BTW I find it beneficial to delay onset of the mechanical advance until at least
a few hundred rpm above idle, so that the advance mechanism can not affect idle
speed. This involves adding more preload to the springs so that the advance is
delayed, reducing the amount of total mechanical advance that can be added, and
then setting the idle with more initial advance. This doesn't change the curve
in the 2000 and up rpm ranges, it just flattens it out at idle and prevents
fluctuation in idle speed from being magnified by the resulting fluctuations in
timing.
Having said all that, I do not recommend any of this for any but the most die
hard power junkies. Or folks with a fair amount of experience.
Gerardo Magana wrote:
>
> Ok, good points, but how do you explain the black liquid stuff spraying from
> my exhaust?? What could be possibly causing this. I have a new engine and
> have driven it easy and not hard as it is going through the break in period.
> Maybe you can convince Elayne that you need to come to Modesto to look at
> this, hehe.
> Gerardo Magana
> ----- Original Message -----
> From: Ronnie Day <ronday@home.com>
> To: Marc Sayer <marcsayer@home.com>; Roadster List
> <datsun-roadsters@autox.team.net>
> Sent: Friday, July 20, 2001 4:15 PM
> Subject: Re: Solex, running rich??
>
> > Good points, Marc. Now..., how do you cross relate those two aspects, the
> > ignition and the mixture? I know the basic process of tuning the
> Solex/Weber
> > types from the idle circuits up through the RPM range, but can you go
> > through a similar, somewhat independent, process and optimize the timing?
> Or
> > at least can most of us who don't have a chassis dyno and exhaust gas
> > analyzer in the garage? It's times like this that make the new digital
> > engine management systems attractive. Just plug in your laptop and map the
> > fuel and ignition curves.
> >
> > BTW, I haven't forgotten the step by step Solex/Weber tuning guide that I
> > mentioned some time ago. I'm digging around for some info I know I have on
> > starting points for jetting, so I can include it, too. I put it in one of
> > those places so safe now I can't find it! Doh! I need to order Hammill's
> > books on Webers and SUs anyway. Maybe I can convince Elayne I really need
> > them now.
> >
> > Ron
> >
> > Ronnie Day
> > ronday@home.com
> > Dallas/Ft. Worth
> > '71 510 2-dr (Prepared Class Autocrosser)
> > '73 510 2-dr (Street Toy)
--
Marc Sayer
82 280ZXT
71 510 2.5 Trans Am vintage racer
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