I have chased the cause of too much fuel exiting from the rear carburetor overflow of my AH100 for years. These are SU H4 carbs-very simple design, but must be done correctly to perform. So I find that the jet is out of center and piston is sticking up above the flat about 1/8″-that would allow fuel to run into throttle area and out overflow drain tube.
However you can never outguess an LBC. What was thought to be a carburetor leak or overflow turned out to be a fuel line fitting.
Issue was not the floats; not the needle valves; not too much fuel pressure; not cracked covers or bodies-it was a FUEL LINE LEAK. Discussed on the phone and solved by COCBCC club member Michael Meindorfer, whos comment was “it has to be external”.
Sure enough, the fuel line compression fitting just below the drain tube was shooting a tiny geyser directly onto the drain tube (location seen in photo) which then ran down the copper pipe to the ground! It appeared to be overflow. Somewhere in the 50s the pipe was altered and a fitting added that was not well done and let just a fine spray of fuel escape. Fuel line off the car to get replaced. Garage stinks of petrol but issue is solved…now I just have to crawl, with this old body, back under and fish the new fuel line back into position connecting the fuel pump to the flexible line (this is the hard part).Did it-no leaks! Crawled out and took the car off the jack stands. Done.
