Hi Scott,
>
> ~ 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.
It does go on for a bit longer ...
>
> 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).
The mixture is rather rich at the moment... I also took the B to one of them
'computer tuneup
places' and the chap there stuck this probe in the exhaust to measure what was
coming out and
he showed me that there were 1500 parts of unburnt fuel in a million. He also
said it should
be more like 200 parts in a million. Dunno how much this is true, for this type
of car etc...
>
> Second: did you remember to set the timing with the vacuum line
> disconnected?
Yes ..
> 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?
Yes, I drained it a couple of weeks ago, and filled it with Castrol
coolant/rust inhibitor
with a ratio of 30/70, so I'd better increase the ratio when I get home this
evening.
> 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
> Mine is a 67 mark 1.
>
> 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
>
One mechanic who works only on MG's said that the I should also check the
compression and that
150lbs or less I should be ok. 150-170 would cause some run-on, but can be
fixed .. 170lbs +
would definitely cause runon.. How does this affect the above ??
Thanks again for the info .. shall try a complete re-check of all the timing,
float bowl levels
mixture, etc ...
--
hiran.
_--_|\ Hiran Wijetilaka email: hiran@ee.uts.EDU.AU
/ \ Computer Systems Engineering voice: +61 2 330 2372
\_.--._/ University of Technology, Sydney fax: +61 2 330 2435
v PO Box 123, Broadway, NSW 2007, Australia.
If it doesn't smell, it isn't multimedia !
|