| I would like to cover a
problem I would often come across while I was tuning MGs at European Sports Cars - not
being able to control a very high engine idle speed. Many things can cause a high uncontrollable idle speed, I will
cover some of the things I found. One would be worn or broken by-pass valves in the carb
butterflies, or worn butterflies and butterfly shafts, always look for vacuum leaks around
the carb and manifold.
Another problem I found was the
distributor vacuum unit, especially on the late model 1500cc Midget. This vacuum unit is a
vacuum retard unit and would hold the ignition timing at 2 degrees after top dead center,
if the unit failed, the timing would advance thus changing the idle speed.
On the 1973-1974 MGB you must have the
absolutely correct distributor vacuum unit. As I found many of these model cars with the
wrong vacuum unit fitted, which allowed too much vacuum advancement which in turn
increased engine idle speed.
I think I’ve touched the tip of the
iceberg in this article, but I hope this has helped at least some of our members.
Paul Lewis |
