Sunday I decided that I should check the timing on my 73 MGB GT. I found
the timing to be at 10 degrees AFTER TDC. So I checked the manual and it
says for a 18V engine with a 25D distributor, the timing should be at 13
degrees BTDC. I adjust the dizzy to 13 and of course the car now barely
runs because the carbs were setup to work at 10 degrees ATDC and are way out
of whack. I mean the idle screws were completely backed off and the jets
were all the way down. So I adjust the jets and idle by the book and had
the car idling around 800 rpm. The car is running smoother than ever
before. Take it for a spin and it is pinging under any type of load. Ah,
unleaded gas and lower octane fuel! So I backed the timing off to about 7
degrees BTDC. Take it for another spin and the pinging is gone but is
replaced by a bit of backfiring when I lift my foot off the gas pedal. I
checked my plugs and they are a nice brown colour so my mixture is about
right. It is also not idling very well, but I am guessing that it is just
an adjustment of the idle screws due to adjusting the timing again.
The question is what should the timing be for my car given that we don't
have leaded gas? Also, any suggestions as to what is causing the car to
backfire?
Mark Jones
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