~ Hi Folks,
~ Seems like the ol' B is not quite right after the tune-up and work on the
carbs (twin SU's)
~ The timing has been set to 10 degrees and the float levels to the appropriate
1/8". The
~ plugs have been correctly gapped along with the points (new plugs and points)
~ When the engine is warm (ie. operating temperature) and it is turned off it
runs-on. This
~ problem does not exist when the engine is cold .....
All together now: "They all do that. :-)"
Seriously: this is a known, um, "behavior" of B Series engines, at
least those made before 1972. The low-compression variants (18V with
8.0:1 CR) don't tend to run on; the earlier 8.8:1 versions are much
more likely to, particularly with low-octane gas. Most early Bs will
give a little stutter on shutoff; the question is how LONG they run
on. If it just sounds like a horse fluffing air through its lips once,
that's okay. If it goes on longer, you may want to take steps to
correct it.
First: get the mixture correct. Oddly, this is one place where you
may end up enriching it rather than leaning it out, as lean-running
tends to heat up the combustion chambers, causing worse run-on than
if you'd run it too rich (which you'd think would make it easier to
ignite, but doesn't because it's cooler).
Second: did you remember to set the timing with the vacuum line
disconnected? That's a common problem, and it ends up with your
timing too far advanced, sometimes by as much as 6 or 8 degrees,
depending on your model year. Cars too far advanced will also run
hotter, which adds to the problem.
Third: Have you recently refilled the cooling system? Be sure it's
been bled; Bs are less touchy about this than some cars, but you need
to run the engine with the radiator cap off till the thermostat opens,
then add coolant (preferably water) till it's full. You might try
flushing the system if you haven't lately, and remember that a higher
concentration of glycol actually *retains* heat; you want a mix of
glycol and water. The standard ratio is about 50-50 (it's actually
54:46 but I can never remember which is which :-), but if you want
to improve cooling, run as much as 4:1 water:glycol, or use a cooling
system enhancer like RedLine's Water Wetter (be sure to get the one
that has corrosion inhibitors and water-pump lubricants).
If you've already done all of this, well, old car's aren't new cars,
and an occasional shudder as you turn the car off is actually to be
expected from early high-compression MGBs --that's 1971 and earlier;
if your car is newer than that and does this, you may have faulty
emissions components or bad vacuum lines. Some model years -- Randy
must know, I've never needed to learn which ones -- have anti-run-on
valves which manipulate the fuel pressure to keep gas from being
sucked in once you turn off the key. If you have a real problem,
you can try retrofitting one of these valves. But my advice is to
learn to think of it as an endearing trait of a car from a different
time. :-)
--Scott "Like a spouse who uses a different toothpaste protocol" Fisher
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