Tech Tips: Spring 1995

I enjoy getting your newsletter very much and when it arrives I devour it cover to cover! I especially enjoy the Tech Tips and Under the Bonnet features and get a lot of useful information from them. Owning a 1976 MG Midget can be quite a challenge at times!

Recently every 50 miles or so, I had to top up the dashpot with oil, and this got to be a pain after a while. The Midget has a Zenith CD 150 carburetor which has been rebuilt. This carb has an adjustable metering needle that adjusts using a special tool. To adjust the needle, there is an adjustment screw at the bottom of the dashpot and this screw has an O ring that is supposed to keep the oil in.

After taking the top off the carburetor, I removed the air valve from it, and, holding the air valve upright, I filled it with oil. Placing the damper in the dashpot and looking at the bottom around the metering needle seat, I pressed the damper assembly down. Oil would leak out every time I pushed the damper down! The next problem would be to get the adjusting screw out of the dashpot.

Looking at the diagram of the carburetor, I noticed there was a retaining ring holding the screw in. Trying to pry it out from the top was not the way to do it! The only way was to push it from the bottom. So I removed the needle, and after pouring out the remaining oil, started to look around for a rod or something that would work. Having no rod but having a nice set of nut drivers, I tried these, and finding one that was a fairly good fit, I began to press the screw out along with the retaining ring. Checking the O ring on the adjusting screw, I found it was hard and worn after some 18 years and needed replacing.

I had a set of O rings, and, selecting one that fitted, I replaced the screw and retaining ring in the dashpot. I pressed everything back into place with the nut driver, making sure the O ring was snug and sealing the screw. Finally checking that it was easily adjustable, I reassembled the carburetor and it hasn’t leaked since! The Midget does not now miss on acceleration, and it’s also nice not to have to get out of the car every 50 miles or so to top up the dashpot!

—Chris Lutz, York Haven, PA.

Earlier this year, both the fuel and temperature gauges on my 1978 MGB went “flop.” I followed the suggestions offered in your MGB Catalog, version 4.2, page 65, to no avail. Using your recommendations, the gauges tested okay. Replacement of the temperature sending unit yielded no improvement. I decided to replace the voltage stabilizer, and since installing it (what a pain!) the gauges appear to function properly.

May I suggest that you add the voltage stabilizer as a possible cause of fuel and temperature gauge malfunction (at least if they go at the same time). I noticed that the new stabilizer showed a resistance of 3.17 megohms between the two lugs. The old one had electrical continuity which indicated a short or similar malady.

Can I, in closing, suggest that the item listed as the ballast resistor in the MGB catalog be amended? This item is actually the drive resistor for the coil.

—Robert Galli, Des Plaines, IL.

Some of our NAMGAR members have had a heck of a time getting a good gasket seal when changing out the gas tank sending unit on our MGAs. Troublesome gasket leaks can occur at the main gasket, at the smaller rectangular gasket on the front of the unit, and at the electrical connection stud at the bottom of the unit. The rubber gasket that currently comes with replacement units has a tendency to squeeze out after a short exposure to gasoline and can present you with a real gusher!

Our fix is to make or buy cork gaskets to replace the rubber ones and to liberally apply Hylomar Hi-Temp gasket dressing to all surfaces. This stuff is gasoline-resistant and withstands the tests of time. It can also be used successfully at metal-to-metal connections where a small gasoline leak is a problem, such as the fuel pump filter access nut.

Without using “S19” or something similar that works as well, you could easily find yourself with the garage floor covered in gas after changing a sending unit. Highly dangerous—’nuff said!

—Don Holle. Albuquerque. NM, Registrar of the North American MGA Register.

Many owners of American collector cars will routinely pour in a small quantity of light oil into the running engine (via the carburetor) just prior to shutting down for the winter. This is done to provide the interior cylinder walls and valve surfaces with a protective oil coating during storage. While I’ve found this practice to be useful, it is necessarily quite difficult with the side draft carburetors some of our British cars use, including the Strombergs on my TR6.

Fortunately, the marine industry has developed a product specifically for this purpose. Available in most any marine supply shop under several brand names, it comes in a spray can and is known as Fogging Oil. This material can be sprayed into the carburetor for the same desired effect and is sprayed into the engine until a blue exhaust smoke is noted, at which stage the engine is shut down with the oil spray continuing. Naturally, all of this material is burnt off immediately the engine is restarted come spring.

—David Waldorf, Coraopolis, PA.