Concerning an MGA carb not responding to adjustment. I had this problem
and it turned out to be caused by the jet on the rear carb hanging up after
the enrichment device (it isn't a choke per se) was used. The jet on an H4
is a tube with a yoke on the bottom end. The tube slides up and down
inside cork glands for adjustment and for enrichment. Under normal
conditions, the enrichment lever, which is attached to the yoke on the
bottom, holds the jet tube up into the carb body using spring tension from
the enrichment control spring. The mixture adjustment nut acts as the stop
for the jet. So, for the adjustment nut to work, the jet has to slide
freely in the gland and the enrichment control lever / spring has to hold
the jet up against the mixture adjustment nut. Try reaching under your
rear carb and pushing up on the jet tube yoke. The A's jet moved up when
forced and the engine immediately ran different. I ended up taking the
area apart and reassembling it so that the jet slides freely. I didn't
have new cork glands at the time so now my back carb weeps ever so
slightly. I have new corks now and I will fix it as soon as I get the urge
to sacrifice some hand skin to MOWOG.
Why do rich mixtures run cooler? I don't remember but the fact is that
they do. Don't look a gift horse in the mouth. I think it has something
to do with the speed of combustion controlling maximum pressure and, hence,
maximum heat conduction as much as the actual peak temperatures althought
exhaust gas temp drops when the mixture is rich.
On that subject, I leaned the A another flat this week. The idle is more
stable and you do have to use the choke to start it. It is also slightly
cold blooded now- doesn't like accelerating until fairly warm. It may be
just my imagination but I also think that it doesn't pull quite as hard.
It seems to run about 10 F warmer although it is hard to make direct
comparisons there. I will leave it like this for a while and see if I like
it. I may go back one flat. I definately won't go any leaner.
On the subject of MG performance, after reading what has been posted here
and written elsewhere, it seems to me that the real issue is the MGA / MGB
have their components pretty well matched, performance wise. What does
this mean? It means that there isn't a 20 hp magic fix like you see on
some cars where one component is holding the rest back. When improving MG
performance, you here about the 5-10 easy HP but after that it is a lot of
"changing this is useless unless you change that" type of talk. This means
that real performance gains tend to be expensive since you have improve the
entire system. On an A, the best approach to better performance is
probably a 3 bearing B engine. On B's it doesn't sound like there is an
easy solution. Personally, I have been toying with the idea of renting
some chassis dyno time to "supertune" the A- after I really undersand how
it is working now and get it all right. I expect that just getting what
you already have tuned for maximum performance would be the biggest help.
Regards,
Bill Eastman.
61 MGA tuned by ear by a person who is tone deaf
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