On Wed, 21 Jun 1995, W. Ray Gibbons wrote:
>
> One book shows a notched scale that projects out from the timing chain
> cover toward the harmonic balancer. Where is it supposed to be? I
> cleaned off the cover, and can find nothing attached to it or pressed into
> it. Is it on the top? Which side? I cannot find *anything*. I put the
> timing light on, could see the mark on the harmonic balancer (it was at
> about 10 o clock as you face the front of the engine) but no sign of a
> scale anywhere near.
>
This is about the right place for 10-15 degrees BTDC on my 18V engine.
There were engines where the indexing comb was on the bottom side of the
balancer too, I think.
> Question 2: With the engine idling at an indicated 1200 rpm, revving the
> engine does little to the position of the balancer timing mark. It is
> hard to say what disconnecting or reconnecting the vacuum advance does to
> the timing mark--not a lot, I think. I tried turning the vernier adjust,
> and it was frozen. Does it sound as if the centrifugal and vacuum
> advances are not free? Good grief! When I pull the vacuum line off the
> vacuum advance, the engine speeds up noticably. I assume it is running
> very rich, but if I try to lean out the carbs it runs worse.
>
OK... pull the vacuum line off the advance and PLUG IT.... does the idle
drop back to 1200? If so, you are right about the rich/lean business..
Otherwise your timing is either very screwy or you have a vacuum retard.
Turn the engine off and connect the vacuum line back to the distributor,
and disconnect from the carb or intake manifold (by the way, which is it
connected to now?)
Take the distributor cap off and try to twist the rotor. It should give
about 20 degrees in one direction. If it doesn't, then your centrifugal
advance is frozen/jammed. Drip some oil in the shaft per the shop manual
and twist on it some more (gently.. you should be able to move it fairly
easily with one hand, but not easily with two fingers). I had the
advance rust up on me and this freed it (temporarily). I did end up
rebuilding/greasing the distributor.
OK, take the hose connected to the distributor and suck on it (yuck). It
will act in one of the following ways.
1) You can suck all day and nothing happens... you don't even form a vacuum.
2) You can suck gently and the breaker plate moves
a) In the direction you were able to twist the rotor or
b) in the opposite direction
3) You can suck hard, about at the limit of a straw stuck in the bottom
of a thick milkshake, and the breaker plate moves in direction a) or b).
4) You can suck hard and nothing moves.
#1 means a punctured diaphram or bad hose. Replace advance/retard.
#4 means a frozen advance/retard mechanism or breaker plate.
#2 means you have an advance/retard which should be attached to the
carburetor (venturi) vacuum. It will be slammed all the way to one
stop if the vacuum hose is attached to manifold vacuum. It may also
show up as a vacuum leak under that condition.
#3 means you have an advance/retard which should be attached to the
manifold vacuum. It will show little or no response if attached to
the carburetor (venturi) vacuum.
I >think< direction a) is retard and direction b) is advance. I hope
someone will correct me on that.
Over the years some Britcars switched from vacuum advance to vacuum
retard (some had both at the same time) so it can be quite confusing.
> Question 3: the books say to balance the carbs, then to adjust the jets
> of the two carbs in the same direction simultaneously, one flat at a time,
> seeking the fastest idle. But what if the mixtures of the two carbs were
> radically off to start with? Say one was lean and the other rich. As you
> make both richer, one gets righter and the other wronger, or vice versa.
> What do you do then? Is the only approach to bring both jets up to the
> bridge, lower each 12 flats, and start over?
>
As confusing as this whole mess is, you better go 12 flats (the key of
Q, a favorite of Bela Bartok) and start over. This will get you close
enough to fix the distributor.
1) "zero" the carbs (as you describe in Q3)
2) Check the centrifugal advance as above.
3) figure out whether the vacuum unit is designed for manifold or venturi
vacuum, and connect it to the proper source. Make sure there are no
other vacuum leaks.
4) After you get a reasonable response in terms of timing to throttle
advance, take it for a drive. Listen for pinging (to far advanced) or
sluggishness and heat (to far retarded). Adjust accordingly.
5) Now, if you must, mess with the carbs.
John M. Trindle | jtrindle@tsquare.com | Tidewater Sports Car Club
'73 MGB DSP | '69 Spitfire E Stock | '88 RX-7 C Stock
Home Page: http://www.widomaker.com/~trindle
"Gerrold's Laws of Infernal Dynamics:
1. An object in motion will be heading in the wrong direction.
2. An object at rest will be in the wrong place."
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