QuestionI bought my 74-1/2 B 22 years ago and it still has the weber downdraft mod it came with. I've always been able to get her started and running smoothly every season, so I haven't yet broken into the engine; but I have done a minor carb rebuild last summer when the float ruptured and lost it's "floating" qualities. Last fall, after having driven to a friend's house, it started fine, but when I attempted to accelerate onto the main road, it stalled, bucked, and quit. It re-started immediately, yet repeatedly stalled when I put any sort of load on the motor. I towed her home, pickled her for the winter, and now I'm trying to trouble-shoot. This Spring it still starts and idles fine, and sometimes accelerates OK, but usually balks above idle. The fuel filter has fuel flowing through it, although it doesn't seem to be much, air filter has been cleaned ( and even removed, with little improvement) and the fuel pump is clicking. I'm thinking there might be a partially clogged fuel line, or something is amiss in the carb. Where would you suggest I concentrate my efforts?
AnswerWell, my best advice would be to take it off and throw it away. The early MGB SU HS4 side bowl design carb is far superior to the Weber and despite the associated problems they are the best for the car and offer superior performance and exceptional service when adjusted properly.
As far as the Weber goes, Take the choke pod off, hang it off to the side and warm it up. Take it for a spin, see if that helps. Stick a finger in the inside of the tailpipe and note any soot. Fluffy soot indicates a rich condition which also points to possible choke. Remove the fuel line and blow through it with compressed air. Another thing that is a Weber unique problem is a leaking accelerator valve that causes air bubbles that spontaneously purge themselves and return to normal operation for brief periods. Check all vacuum lines and replace any dodgy lines. Remove the distributor cap, remove the vacuum line from the carburetor end of the vacuum advance and suck on it while watching the breaker plate. See if the advance is moving the plate or if it is just drawing air. Turn the rotor with your fingers, it should turn a little and when released, spring back to its normal position. If it is equipped with an early distributor you can have the dwell checked. Remove the spark plugs, white or tan insulators indicate a lean or normal running condition, black indicates rich. With all that done you can go on to rebuilding the carburetor if you find that it suffers from an excessively lean or rich condition. The problems you are experiencing sound more like ignition than carburetion but it is impossible to tell without seeing the car in person and laying hands on the matter. Don't jump straight to replacing ignition components on my gut, run through the tests and if you are unable to find a problem in any of the other systems "and the plugs look good" look to ignition components such as the amplifier and ballast resistor.
Any questions feel free to ask.
John
