Hi all,
My 1975 MGB is running, in general, really well. Probably the best since I
bought the car, considering I've replaced crimped air filters with K&N's,
replaced a faulty fuel tank, pump, and filter, new spark plugs, wires,
distributor cap and rotor, etc. I worked with Chris Kotting to adjust the
valve clearance, distributor point gap, dwell, and timing, and things are
generally great.
Now when I start the car, until it is clear up to Normal temp, I will get
poofs (backfires?) through the air filters. This happens occasionally at
speed, too, even when the car is warmed up. Fortunately it didn't happen
while in a local parade with a 6-year old on the hood, how embarrassing
would that have been? :-)
I've been told that this is because the mixture is too lean, the mixture is
too rich, and the timing is off. Well, even I know that the first two
options can't both be true. But I still don't understand dwell and timing
well enough to know if those would be the problem, or part of the problem.
If timing is the issue, what does retarding or advancing do? Or does one
just try it one way, and if the problem gets worse go the other way?
I've tried looking in the Archive, and working through various tuning
guides, but I need to work through with a human I guess. For example, how
does one measure the gap between points, when the two surfaces are curved?!?
I'm sure several of you can point out in a flash why I get poofs of smoke
through the carbs (twin SU's, not the stock ZS). The plugs seem to indicate
that the mixture is ok, although the tailpipe is black and the exhaust
smells bad. Also, in addition to the poofs, I get a gurgling sound from the
exhaust when, for example, gearing down to descend a steep hill. Reinacting
this sound really entertained the local AutoZoner...
Also, does anyone have a good Work Log template I can copy?
Thanks,
-Mark
Topless Smurf ('75 MGB):
http://www.bones.org/torch/photos/mgb/mark_mgb_1.html
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