Hi All,
I normally ask the list a lot of questions, but this time I hope I can
save someone some major aggravation.
In the year or so that I've had my 74 TR6, I could never get the idle
from running somewhat rough, or uneven. I checked the hoses, the carbs,
the timing, etc. I soon thought it was just normal for the car.
This week, by accident, I finally discovered the problem to be a
defective anti run-on valve.
With the engine running, this valve is not energized which is normal.
The unit should only energize when the ignition is switched off and the
oil pressure still registers for a second, or two. Once the oil
pressure falls, the unit de-energizes.
But did you know, that in addition to the valve at the bottom of the
unit, the one you can push up with your finger, there is also one inside
the unit. If you look carefully at a cross sectional diagram, you'll
see it. This "second" valve should hold a vacuum at all times except
when the anti run-on valve energizes.
To see if yours is working correctly, start you engine and let it idle.
Pull the hose, from the canister, that goes to the intake manifold. You
should see a noticeable change in the idle which indicates it's working
fine.
If you see no change in idle, put your finger on the end of the hose.
You should feel a suction/vacuum and your engine will idle much better.
What you have just discovered is a major vacuum leak caused by a faulty
valve within the anti run-on valve unit.
To fix the problem, either replace the anti run-on valve, or just cap
the end of the hose that you pulled off the canister and disconnect the
wiring to the unit. Unless your car diesels when you switch off the
ignition, the anti run-on valve is not necessary.
I'd be interested to see if others find the same problem.
Regards,
Bill
Atlanta
74 TR6
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