For any of you following my previous message about my ignition timing, I have
some info that may be interesting to the whole group (and some that I am sure
is not). The previous problem was knocking at 4000 + rpm (according to my
inaccurate tach), with a well set (statically) ignition. The car is a 67
MGB.
First, I do (and have since I put in a rebuilt high compression engine) use
premium gas, 93 or 94 octane.
I changed the plugs. Had Bosch W7DC plugs (as should be), and I put in Bosh
Platinum WR7DP plugs (as specified by the bosch books for MGB 62-80). This
plug is also sold as number 4116. Picked them up at K-mart for $7.96 a set.
These are resistor plugs (hence the R before the 7) whereas originally the
plugs were not. By the way, my previous plugs had a lot of carbon deposits,
so, probably running rich / idle is high. For anyone reading the original
MGB drivers manual that says to use a Champion N3 spark plug for competition
(it is a colder plug) you can find them with motorcycle and snowmobile plugs.
I re-set the ignition by ear ... so, set it, drive, accelerate hard, listen
for knock, retard or advance as required, repeat ad nauseum. When I just got
rid of all the knocking, I checked the timing dynamically at about 700 rpm (I
did have to change the idle screws). The mark shows I am right at top dead
center (which is at least 6 degrees retarded according to the numerous books
I have). The car runs ok, but doesn't accelerate as well. I will run it this
way for a couple tanks of gas (once I re-check the carb balance), and see
what kind of mileage I get.
According to the owners manual idle should be 500 rpm, this seems low, I am
shooting for 600-700 now (it was previously about 1000).
I also checked my tachometer by using an instrument from work. It works by
putting a reflective strip of stuff on the front engine pulley, and shining
this frequency meter light at it. My tach really does read high, but it is
not consistant across the range. Maybe I'll adjust, or if someone knows how,
please let me know. I have already rewired for negative ground, so I do not
fear this kind of stuff.
Now I need to double check the carb balance, as I adjusted the idle screws,
but do not have an air flow meter thingy (I plan to pick one up this
weekend). Or maybe I'll take off the air filters and do this by ear too, I
was a musician in a previous life (some 5 yrs ago, not hundreds of years
ago).
Any comments or suggestions welcome!
Phil Bates
67 MGB
75 Jaguar XJ12C
52 MG TD replicar (VW)
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