At 01:31 PM 6/21/95, W. Ray Gibbons wrote:
>
>Question 1: On the trail of the cause of the rough idle, I tried to check
>the timing last night, and there do not appear to be any timing marks on
>the timing chain cover. The engine is a 69 (I said earlier it was a 68,
>but the owner was wrong--it is an 18GH engine with a number under 8000).
>
>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.
>
My engine is also an 18GH series also. The scale is actually on the
bottom of the timing cover. If yours is there too, having the timing mark
at 10 o'clock begs all sorts of interesting questions. Like, why does it
run at all?
>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.
>
Put a little WD40 on the vernier. They tend to rust and freeze up.
Revving the engine should produce a significant timing change. Sounds like
you need to pull the distributor and take a look at its innards. Remove the
points plate and see if it moves freely. These get worn out and really
screw up the timing. While you have that out, check the advance weights
and springs which are underneath.
[BTW, does anyone know where to get replacement advance springs?]
The vacuum advance has a rubber diaphragm which seems to rot really
well. :-S Put a piece of hose on it and see if the advance moves when you
suck on the hose. If you hear a hissing sound and get a stream of air,
your diaphragm has rotted.
>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?
>
How are the throttle shafts? They should have no noticable wobble. If
they do, 1200 may be as low as you can go. The mixture can be set for each
carb individually. There is an excellent SU tuning guide on the FTP site.
I especially like its creative use of Guinness Stout.
Dave "Don't worry, B happy" Ambrose
----
David Ambrose, Proxima Corporation ambrose@prxm.com
Play it cool, play it cool, 50-50 fire and ice -- Joni Mitchell
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