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MGB MGB laying low

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MattP

MattP

Jedi Knight
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My 77 B has the running-on problem, just last night I found the tip on MOSS to fix it, but too late unfourtunately. I got home this morning after work at about 6am. After shoving it into first gear and setting the parking brake, I didn't wait for it to stop dieseling. The result was loud backfire that had to wake half the neighbors. Like gas in an elevator, I looked for someone to blame, I was the only thing in the area. I nearly got out and lay down in the grass acting like I'd been shot, but finally settled for skulking inside.

Later after taking out the trash, I died laughing thinking of the fictional nosy neighbor peeking a while after hearing a gunshot, and then seeing me carrying trashbags to the curb.

I'll be tuning and moving a diode this weekend without fail.
 
I had an old Jeep Cherokee that did that. If you only drove a short distance (like I did for the job I had when I got it) it would diesel and give a "pud" out of the pipe. But then I showed up for the firt day of work at a major plant, up on the side of a hill about 25 miles from my house.
I haden't driven it that far in quite some time, and when I got there I forgot to dump the clutch to prevent the run-on. So it backfired with the report of a howitzer, echoing across the vally, and sending several other people, also arriving to work, either jumping, ducking, or running for dear life.
I was sure plant security was on thier way, and I proceeded to slouch in my seat, barely peeking out the window for several minutes till the coast was clear.
I think it was funny now, but at the time.....
I loved that junk, I mean Jeep.
 
We've had a similar problem over the past 20 or so years! Our 1984 Camaro(retired as the daily driver 2 weeks ago) has a VERY loud magnaflow exhaust system and the way our house is situated our "friendly" neighbor's bedroom window is right above our driveway....Well every morning at 6am sharp for the past 21 years that Camaro has started with a loud rumble(gets worse as the temperature get colder because the auto-choke makes it run rich). that poor neighbor has been waking to that for a very long time!..........LMAO.......he must have been extremely excited when we bought the almost scilent XK8.

Zack
 
Matt P.
Had the same problem with my '77MGB for years. Finally I said enough. I checked the wiring diagram and discovered that the ignition coil/points were getting feed back through the ignition light. This light is connected to the ignition switch [white wire] and the alternator stator coil [brown / yellow wire]. Turn on the ignition and the stator coil serves as a ground for the light - making it light up. Start the engine and as soon as the alternator starts producing current the light then has positive polarity on both terminals [the light is isolated from the body groung] and the light goes out. The problem was when I shut off the ignition the coil/points were still receiving positive current back through this ignition light allowing the engine to continue to run until the RPM dropped and the alternator producing speed and then the current would stop flowing and the engine would stop, sometimes with a dieseling sigh or with a backfire.
Solution - I cut the wire [white] running from the ignition switch to the ignition light and installed a diode to prevent the feed back, now the engine stops dead when I turn off the key, and the ignition light continues to work as designed.

Regards, Bob
 
My 79B was running on and backfiring consistently until I realized that the hose from the anti-runon valve was disconnected. It was actually just hanging down near the engine and since I haven't had this car that long, I just assumed it was connected. I bought a new hose at ACE and connected it to the intake manifold and haven't experienced runon or backfiring since.
Erik
 
The MGB LE was backfiring and running on when we got it....replaced the coil and no run-on or backfiring since.
 
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