The New England M.G. ‘T’ Register has a long history of providing its members with advice and technical expertise on the restoration and maintenance of our special cars. We present some of our favorite technical articles and tips here for members and visitors alike.
Trying to diagnose a Rough Idle?
ROUGH IDLE: Install a dwell tach. Set the tach to read your engine's number of cylinders. Run the engine to 1,500 rpm and watch the dwell (hook tach to negative side of ignition coil). If the dwell varies up and down past the specification for your engine, you can suspect a worn upper distributor bushing. Remove the distributor cap and rotor, grasp the shaft, and try to move is back and forth. Movement indicates a worn upper bushing that opens the points too soon or too late, or not long enough to get good secondary saturation.
Another pesky rough-idle problem can be caused by vacuum leaks. These can be tracked down by using a propane torch. Open the torch valve enough to hear the gas hissing – don't light it. With the engine running at idle, point the tip of the torch at possible vacuum trouble spots – inlet manifold gaskets, carb base gaskets, emission hoses. Move the torch slowly, and when you find the trouble the engine will smooth out and rpm rises.
PLUGS: When tuning-up your car, new or old, pay close attention to your spark plugs. Set the proper gap for your vehicle. Always make sure the electrodes line up. Most often, they do not, but they can be easily aligned with needle-nose pliers. Always adjust the bottom electrode to line up with the center electrode. Then, set the air gap to specs. When installing spark plugs in tight places, use a piece of 3/8 inch rubber hose about 4 inches long over the tip of the plug to help guide it to the head and start the threads. Never reuse a spark plug that has been dropped on the floor.
SPRAY TEST: Still have a miss? Fill and empty pump spray household cleaner dispenser with water and mist the engine with the water while it is running. A bad wire, cracked coil tower will let out a lightning bolt when the water hits it!
by Dennis Koons
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Disclaimer: All Tech Tips presented here are copyright of The New England M.G. ‘T’ Register. Be advised that every effort was made to verify the validity of each tip. But as in any free advice, it’s up to the user to judge the usefulness of each tip presented here.