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MG MGB Technical - Need Help! Engines Runs Rough!

Ok. I am lost on this one.

New Early Camshaft. Lined up with dots. #1 and #2 valves closed (Has Clearance, TDC mark on Pulley lines up with TDC mark on timing cover. Distributor rotor points to #1 spark plug or at the 2 o'clock position. Plugs at 1,3,4,2 counter clockwise.

This all seems correct. If I was one tooth off would not the timing mark on the pulley also be off and not match the TDC mark on timing cover?

Took carburetor off and clean it all up. Basically brand new with only 1000 miles on it. This all seems ok.

Distributor was rebuilt by John Twist with Pertronics electronic ignition. I checked and all 4 spark plugs have spark.

Now when I start the engine I can get it started but I can't keep an idle. If I keep it at a high rpm I can keep it going but soon as I let off the gas it will slowly die down and not hold an idle. The engine really shakes and is not smooth running.

Did everything that I could think of and lost right now with ideas. I keep thinking that maybe I am one tooth off but everything seems to line up. Any help much appreciated.

Regards, Ray
Ray 1977mgb

Ray; Try leaving the distributer loose enough so that you can still move it by hand when the engine is running. Have someone start the engine and then hand time it . You may find it works better that way until you can put a timing light on it while it is running,
Sandy
Hudson Florida
Sandy Sanders

Sandy,

Tried that already and it's still loose while I try to figure out what is wrong.

Here is another hint or clue. When I use the timing light on the #1 spark plug at 1000 rpm the light barely works or flashes. If I raise the rpm to 3000 than the timing light seems to work. Is this a hint of something with the #1 spark plug?

Thanks, Ray
Ray 1977mgb

"Is this a hint of something with the #1 spark plug" More likely something with the distributor cap, rotor, wires or even the condenser (yes, I know it's new - that is most failures occure with condensers).
David DuBois

David,

I read one post that if the timing was off by one tooth this caused the timing gun not to work properly. No real answer if it does. I tried a new distributor, cap, rotor, and wires. Need to try new spark plugs next.

Thanks Ray
Ray 1977mgb

Fixed. Something so simple I just never thought of. Changed the spark plugs and it works fine again. Still can't beleive it was that easy.

Thanks Ray
Ray 1977mgb

Ray. Yes, sometimes it can be that simple.

As to your timing light question, no, what you heard was not correct. The timing light is activated by the spark bridging the gap between center and side electrodes. If there is a spark, you will have a flash of light from the timing light. That is why it makes a good diagnostic tool. Remember the pattern of flashes you describe--weak/intermittent at idle and stronger at higher engine rpms?

This was, in reality, a weak/intermittent spark all the time. At the higher engine rpms, the timing light was being triggered more frequently so it seemed as if you had a stronger spark because you had more flashes per minute than at idle.

You are not limited to using the timing light only attached to the number one cylinder. Moving the timing light connection between the cylinders, while flashing the light onto the inner fender or engine block, will allow you to make a rather coarse judgment about how well the cylinders are firing as compared to the other cylinders.

Glad you got it sorted and that it was only a minor problem. Hate it when my MGs are not running properly and I cannot figure out what the problem is. Life is so much happier when the problem is found and corrected.

Les
Les Bengtson

Les,

Thanks for your excellent information on timing lights. I am going to save your post for future information.

Ray
Ray 1977mgb

This thread was discussed on 21/01/2008

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