[T3] Tight exhaust valves

[Dave Pallo]

[[[On the timing issue, I have a '72 and I follow the procedure in Bentley
(roughly: set idle, confirm throttle is closed by pulling 1 dist. hose and
observing timing mark, pull & plug both hoses, reset idle, time, re-connect
hoses, reset idle).  When I have both distributor hoses off to set the
timing, my engine always surges a bit, so the timing mark moves. I just get
it so the center of the swing is the proper timing and assume that is OK.

 

If anybody else has a '72 out there, do you experience this similar surging
at idle when both your distributor hoses are disconnected? It is maybe a
swing from 820-870 (so still within the 850 +/- 50), but enough to make the
timing mark move.]]]

 

Following the Bentley timing procedure is the right thing to do. It tells
you what to do (but not why), so if you follow the Bentley directions for 72
- you'll time it correctly.

 

.         For a 72, it is very important that the throttle plate fully
closes. This enables the vacuum retard port to have vacuum at idle (also
very important). A correctly adjusted throttle valve switch will not stop
the throttle plate from closing fully.

.         The idle speed screw does not provide a mechanical stop for the
plate (as in carbed engines), but instead allows a very small amount of air
into the IAD to control idle speed. This screw will not hold the throttle
plate open at all.

.         For a '72, the vacuum retard is what pulls the points plate back
AT IDLE and makes it possible to achieve the 850 rpm at idle. That is why we
have vacuum retard. If you are correctly timed at 5 degrees, and your vacuum
retard is not working - you more than likely won't be able to adjust the
idle speed screw enough to get the idle down to 850 rpm.

 

This are some reasons why you have to follow the Bentley. The '72 motor
needs to be timed at 850 without vacuum influence, but as soon as you
connect the vacuum lines; the points plate moves - and so will the timing
marks, and therefore the idle speed. That's why you are going back and forth
with setting idle speeds when setting the timing.

 

The surging you are seeing is not good for timing a motor - any motor,
regardless of year, FI or carbed. This is not a '72 thing. You are probably
correct in looking for any vacuum leaks, as that will cause surging. It's
probably not your golf tees, as we all use 'em ;-) 

 

And Thanx for the props, Bob! Experience is the best teacher, isn't it?

 

 

Dave Pallo

'72 Square ~ Elwood

Fairport, NY

 

 

 

 

 

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