I am at a complete loss now. I've tried everything, and my MGB is still
not running right. Last night I installed a new timing chain and tensioner
only to find that the car still exhibited the exact same symptoms as
previously. The old chain had stretched some and the tensioner pad was
very shot, so it needed to be replaced anyway, but even though the timing
no longer bounces around like crazy, the car still runs crappy. I need
your help!
A little history is in order for those who haven't been following my car's
saga this summer. This is a '74 MGB roadster with a '69 engine in it.
After running flawlessly for over a year, problems started in the beginnning
of June when I drove from here to Columbus, OH (~75 mi each way) for my
first ever autocross. The car was running fine, but I hit a pothole on
I-70 (hard to believe, I know) and my muffler got knocked off. I got it
jury rigged back into place and drove the autox. After running fine for my
first couple runs, it began to miss and backfire under hard acceleration.
It ran fine on the drive home, though.
It continued to run fine for about a week or two and in the meantime I
replaced the two part muffler with a pipe and a cherry bomb. It still ran
fine, though it occaissionally would miss and backfire when cold. Then
I noticed I was losing coolant out the side of the head. Off came the head,
on came a new gasket. Problem fixed, car ran great for about 10 miles,
then the backfire problem got worse than ever.
I swapped distributors. No real change. I swapped coils. No real change.
I put in new plugs. Some improvement, but not a lot. I looked at the
compression and it seemed okay three ~160psi, one around 170psi. I
rebuilt the carb (a Weber 45 DCOE 9, jetted 130 main 170 air correction,
I think.) This helped a little too, but the problem persisted. It was
suggested that my timing chain might be bad and since you could see my
timing bounce all over the place when the engine was revved, this seemed
logical. So I took it all apart and last night got the new timing chain
installed. The car started after a few tries, but ran poorly. I turned the
distributor until it ran smoothly. With it advanced ALL THE WAY, it idles
GREAT (if a little fast) and the timing is nice and steady, even when
revving the engine (at least with it in neutral.) But when driven it
runs the same as before, missing and backfiring through the carb under
acceleration and backfiring through the tailpipe LOUDLY when deccelerating
with engine braking.
So SOL experts, what could my problem be? Tonight I plan to retorque the
head (I know you're supposed to drive five hundred miles, but ...) and
adjust the valves again and hope that solves my problem, but I have very
little faith it will. Any ideas, thoughts, comments would be GREATLY
appreciated, as I am at the end of my rope.
Driven to distraction in Dayton,
Bob Jones
bobj@meaddata.com "So that's why they say driving an MG is like
Mead Data Central driving around throwing $20 bills out the window."
Dayton, Ohio
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