Keep ‘Em Running

I have been working as a professional mechanic since 1974, and my first job was at a Jaguar and Triumph dealership that had recently acquired the MG franchise. It was assumed that I might have some insight into keeping these cars running and performing properly. Many memories come to mind of these early years, and I will try to reflect on one of the better ones, if I may.

A very early lesson I learned was from an old-timer British born shop manager at the dealership I worked at in Rochester, NY. I had just spent an hour or so trying to get a 1974 MGB to idle down. It seemed that no matter what screw I tinkered with on those mysterious things called SU carbs, the idle would not come down lower than 1500 RPM. Very frustrated, I asked him for help, thinking he would just come over and show me what the problem was. Imagine my surprise when he merely started asking me some questions instead.

“Now mate, what do you suppose makes an engine run?”

(Me: still in a bit of a mood) “Well, what the heck do you mean?”

“What do you suppose makes an engine run?”

“Well, air and fuel”

“Ahh…then I guess it must be getting too much of those, don’t you think?”

“I guess.” I was starting to calm down a little and tried to think.

“Where do you suppose that air and fuel come from?”

“Well, from the carburetors.”

“Right you are mate.”

“Well I turned all the screws as far as they go.”

“Well, then maybe it’s time to remove the little blokes and take a look!”

And THAT is how I learned all about the throttle plates used on MGB HIF carbs that have spring loaded valves designed to lower the engine speed slowly for emissions control. When the springs lost tension over time, the valve would stay open, and the idle speed screws became useless. You could solder them up, or replace the throttle plates with new ones.

I ALSO learned a much more valuable lesson….how to slow down and think, and how to teach others how to diagnose! What a great lesson, and how I wish I could thank this man, who I initially thought was a bit of a pain.

Drivability issues are something we deal with in the shop every day. Patterns emerge, and a consistent approach to diagnosis is developed over the years. It starts like this:

Pay attention to the actual problem. Determine if it is intermittent, and when it occurs. Full time problems are the easiest to diagnose, since you can perform all the tests needed to arrive at the solution. You may need this information to get insight from a professional, or when you have to take the car into a shop.

As always, an engine needs S.S.B.B. That’s Suck, Squeeze, Bang, and Blow to the few that haven’t heard this one yet. This also helps to put the diagnostic tests in order. But first things first:

Electrical system condition. This means the battery must be fully charged, and the starter must be capable of “cranking” the engine over at a reasonable speed. Battery voltage test, load test, starter draw amperage: these are all done quickly and intuitively by an experienced technician. In other words, the audible cranking speed and rhythm will determine if he goes any further with these electrical tests.

Suck: This is actually a part of determining the condition of the carburetors, and intake manifold system. This is the intake stroke of the engine, and the air-fuel ratio is determined AFTER the following matters are addressed:

Squeeze: This is called compression. This is ALWAYS the first test that should be done. The results will indicate if one needs to go any further. An engine with low compression in one or more cylinders will never run right, no matter how many screws you turn, or parts you throw at it! Adjust the valves now and recheck the compression.

Bang: This is the ignition system. Here at the shop we use a modern Engine Analyzer that instantly reports on the condition of the points, condenser, coil, spark plugs, and ignition wires. When this equipment is not available, you simply have to trust your eyes. Remove the distributer. (I assume bending over the car for twenty minutes is not something that most people think is a lot of fun). Turn the shaft, and make sure the points are opening. The factory setting is .015, but almost any opening will produce a spark from the coil. Too little or too much of a gap merely reduces the coil available output. Grab the rotor, and turn it counter clockwise. It should move about 1/4 inch or so, and then spring back by itself. This indicates the general condition of the distributer advance. If it does not move at all, you will have no timing advance relative to engine speed, which will result in a noticeable loss of power.

Spark plugs should be cleaned and gapped, or replaced. Do NOT use Platinum spark plugs. They do not fire when showered with the rich mixtures found in carbureted engines, and in fact the Bosch Platinums are despised even by modern car technicians. Spark plug wires should be tested with an ohm meter. Typical resistance per inch of non-solid core wire (modern type) is anywhere from 1000 to 3000 ohms per inch. Solid core wire (what the MGA came with) of course should be close to 0 ohms, the resistance needed for radio frequency noise interference abatement coming from the angled spark plug connectors, which are typically 1000 to 5000 ohms. ALWAYS test these… even brand new ones. More common is corrosion inside the spark plug connector or the distributer cap if you are using the later MGB version. Pull the wires out and look for rust/corrosion. When using the original screw terminal caps, always use an ohmmeter to verify that you have successfully made connection with the wire with the piercing screw.

Ignition system integrity is an absolute necessity BEFORE going to the carburetors and fuel system side of the engine. Of all the times I have heard, “I have tried everything I can think of to the carburetors, and the engine just won’t run any better,” the actual problem was in either the ignition side or the fuel delivery side.

Blow: This is the exhaust stroke. Exhaust systems can change running characteristics of an engine, but for the purpose of this discussion we are assuming a tight exhaust system with no leaks at all between the cylinder head and the inlet of the muffler. A large enough exhaust leak (such as a piece of gasket missing from the manifold) can cause the mixture to go very lean. A plugged muffler (think “Banana in the tailpipe”…ala Beverly Hills Cop ) can cause loss of power or maybe a no-start…but I actually doubt the no-start scenario. Running with no muffler (or just straight pipes) is dangerous for the engine and will lean the mixture out enough to cause damage on a street car.

This leads us to the most common problem facing any classic car owner today, and that is the fuel supply system condition. Modern fuel is NOT going to stay in usable condition longer than three or four months without some type of fuel stabilizer such as StarTron, or Stabil, to name just two. Fuels containing Ethanol offer their own unique challenges as well, the main one being that there is NO additive available to combat the negative effects of having Ethanol in your gas tank. You simply have to assume that a steel unlined gas tank will be coated with rust if is has been sitting around longer than four or five years with bad fuel in it. Just throw it away. New tanks are not that expensive.

If you want to use an internal coating on your old tank, use the three step process from POR15 and CAREFULLY follow directions without skipping any steps. If your old tank was coated internally years ago with what was available at the time, that coating will start coming off if there was any Ethanol fuel used. It is impossible to remove an old coating without cutting the tank open and scraping it out. Once again, just buy a new tank in most cases.

Keep your tank full, with Ethanol free fuel, and drive your car at least once a month for best results. Bad fuel will make the chokes stick, coat the metering needle and jet with a coating of goo, and do a host of other nasty things that will render the carbs useless. Old bad fuel will not burn correctly, causing another batch of wasted time trying to make the car run properly.

To repeat…the proper order of diagnosing a running problem is:

Correct battery voltage, good cranking speed, a working charging system.

Compression test to determine engine condition. At least 125-150 lbs. compression with a maximum deviation among cylinders of 15 percent. Adjust the valves.

Fuel quality and delivery test. Pressure and volume tests. 1 to 4 lbs. pressure and a delivery volume that looks like a steady stream, not a pulse. Make sure there is fuel in the float bowls.

Ignition system condition. Be aware of Black ignition rotors. In fact, just never use them! Be aware of new condensers. Do not replace an old one unless you are 100 percent sure that it is the problem…there are just too many poor quality units out there. If in doubt, change over to a Pertronix Ignitor. (I do not

recommend the Pertronix complete distributers due to quality issues at this time.) Set the timing to approximately 10 degrees before top dead center at idle speed to start with. Final fine adjusting will come later.

Once all of this is perfect, then start in with the carbs. I am not going to go into the carbs in this article. Many excellent articles are available on the Internet and in books. Look at a John Twist You-Tube video. Professionals like John do this intuitively, so don’t expect perfect results without practice and research. I will be happy to address my carburetor adjusting system in a future article.

Glenn Lenhard is an ASE Certified Master Technician with forty-two years experience working on European, Asian, French, and British cars. During the ‘80s as the owner of Bay Imports in St. Petersburg, Florida, he used to “repair Volvos so he could afford to work on MGs.”

Glenn and his wife, Gail, currently own and operate Glenn’s MG Repair in St. Petersburg. They have a staff of five mechanics, two body and paint specialists, and a full time Parts Manager. The business works on all British cars, but Glenn and Gail have a special place in their hearts for the MG make. They have owned the same MGA 1600 Mk II since 1974, and Glenn has restored it three times now, which shows how much use it gets. Gail gets to drive a 1966 MG 1100 when she gets bored with her modern car.

Thanks Glenn A. Lenhard for a great article! You can reach Glenn, and be sure to see the ad for his shop in MGA! magazine.