To Solve a Mechanical Mystery

Last September, members of the Bay State MGA Club met at Fitzwilliam, New Hampshire to caravan to the British Invasion at Stowe, VT. Hurricane Irene had made several of the usual back roads routes up impassable, so we adventured north through Keene and up to West Lebanon where we stopped for lunch at the 7 Barrels Brew Pub. It started raining just north of Keene, and turned into a very wet ride even with the tops up and side curtains in.

Our group continued up VT Route 14 where in several places flooding from the White River had damaged the roadway, but it had been filled in with dirt and stones and was passable. We noticed a lot of damage along the way, but it appeared that those resilient Vermonters were recovering. No problems with any of the cars, they were all running strong, although some complained they had trouble keeping up with me (my MGA has an MGB motor in it). We made it safely to our rented vacation house up a very steep hill that overlooks the ski slopes of Mt Mansfield.

When I started the MGA the next day, it seemed kind of cold blooded. I coasted down the long steep hill to Route 108, but on any inclines the engine had no power. I pulled into a Shell station in Stowe to investigate what might be wrong.

I could get the car up to 40 miles per hour, but acceleration was painfully slow. It seemed to run fine at idle as long as there was no load on the engine. The mechanics at the Shell garage were very helpful and provided lots of advice and tools as needed to investigate the problem. It was a real puzzle why the car ran beautifully one day and would hardly run the next.

I changed all the plugs, the cap, rotor, points and the coil (with spares I carry in the car). While changing the points I found the internal grounding wire to the moveable plate that the points attach to was nearly severed, so, we made a replacement. I had also noticed that the cap was burned by each contact indicating that the timing may be off. After checking, though, the timing seemed to be reasonable. Since we did all these things and it did not change the symptoms, I sought more advice. I limped the car over to the Golden Eagle Resort where some of my British car friends were staying.

We pulled out the distributor and looked at the weights. With the mounting plate off I noticed that the plate that holds the points was moving back and forth (no spring from the vacuum advance to hold it in place). This is a problem because the timing will always be changing, so, I got a piece of wire and twisted it around the stub for the spring and locked it in place. Also, I noticed that the weights were very “sticky.” They could go out, but not return back to base position. I decided to see if I could find another distributor with the parts vendors on the show field since this one obviously had some issues. Sam at Brit Bits (a Moss distributer) had an aftermarket reproduction of the 45D Lucas distributor. It turned out that the replacement distributor drive dog was 180 degrees off from where it should be, so, I had to switch the position of #1 cylinder wire with that of #4 and go through the firing sequence from there. I also verified static timing to ensure nothing had been changed while replacing the distributer by using a test light across the points and the timing mark on the damper pulley.

Well, the engine idled and revved great, but as soon as a load was put on it, it behaved exactly the same way! At this point I was at my wit’s end. I still believed it was something on the electrical side of the engine rather than fuel related. I took the car back to the Stowe Garage and dropped it off and hoped the mechanic would have better success.

On the field at the 2011 British Invasion in Stowe, Vermont.

By the next morning the mechanic had already gone through checking the spark plug gap, points gap, timing, etc and set them to 1959 MGA specs (which is not quite right since it is a 1970s MGB engine and ignition), but the problem remained. I have a Weber DCOE 45 carburetor on the engine. The mechanic decided to examine all the jets in the carburetor. He kept feeling in the rear barrel and saying it felt “wet” (with fuel), but I checked it and it looked normal to me. Then I felt inside the front barrel and I could feel something moving inside which was not happening on the rear barrel. We pulled the intake manifold with the carb off the head and tipped it up so that we could look inside the barrels. We discovered that a lock tab had not done its job in keeping the main jet (which centers the flow of fuel into the middle of the venturi) in place and the jet was revolving and moving in and out, sometime blocking all fuel from number 1 and 2 cylinders and sometimes allowing fuel to flow freely into the barrel, but not in the center to be mixed properly with the air.

This was our “Ah Ha!” moment.

Since this is a metric carb it was going to be difficult to get the right part on short notice. The mechanic took the same bolt from the rear barrel and went to match it with something that they might have around. It turns out that a brake bleeder screw was a perfect thread match. He had to modify the end that goes into the carb so that it would go into the venturi part and lock it in place. He was able to grind it down so that it would fit in. Our next concern was how to lock it in place so that it would not vibrate out like that last one. We reused the lock tab, but also, he took a tire valve cap and cut off the end and it threaded onto the bleeder like a lock-nut and so, it looked like we were in business.

We bolted the carb back onto the engine and fired it up and it was running smoothly. He took it out for a spin and it ran great, he said. I hopped in and drove out of the station. I revved to 4000 RPMs in first and shifted into second. Ran it up to 4000 RPMs in second and shifted into third gear. Then as I accelerated the engine began to falter and the symptom was back! I limped the car back to the garage and gave the mechanic a thumbs down. We popped the bonnet again and almost immediately the mechanic turned around and walked away. He came back smiling and with a bolt in his hand—the one he had removed the bolt from the rear barrel and had not put it back in. We were so excited about the front barrel fix, he had forgotten!

With the bolt in place the car ran great. The engine “pinged” a little under heavy load (even though I was running premium fuel.) But, this was almost expected with having all the timing and gaps set to 1959 standards. I was willing to live with this slight problem until I got back home and made the proper adjustments. So, I paid my bill (three and a half hours of labor) and enjoyed the rest of the day at the show grounds sharing the causes and effects with many of my MG friends who had been making suggestions along the way.

It is amazing that these old cars continue to perform at all, but with just a few tools and spare parts they take us all over the place. With simple preventive maintenance they continue to provide great driving experiences and remain a thing of beauty for everyone to behold.

Safety Fast,
Jack Horner, President, Bay State MGA Club

If you’re interested in the MGA or would like to learn more about our club, visit our website at: www.bsmgac.org.