Bruce,
Clearing the carbs, also called clearing the plugs, means to rev the engine
up after it has been idling for a while. High performance engines in
particular don't like to idle for long periods of time. The idle gets
lumpier and lumpier until the engine dies. I don't think that the carbs
are actually getting backed up. My guess would be that the rich, cool
mixture slightly fouls the plugs and increasing the rpm heats them up and
clears them, hence the second, less common name. Most LBC manuals
recommend reving the engine occasionally while setting the idle or to
"clear the carbs (plugs)."
As far as tuning a pair of SU's, I think that the most important first
step is to get the two carburators set the same. This is where standard
tuning procedures work great. The old "lift the dashpot" aproach will
probably give fairly consistent results for a good starting point.
Personally, I took my dashpots off and measured the position of the needles
and seats and set them at the same point for both carbs using a dial
calipers. I then lifted the dashpots to get them as close as I could.
After that, I am still fine tuning but I always adjust them both the same
amount. I just leaned them a flat two weeks ago because its warmer
outside. I am considering leaning them another flat now to improve the
idle. Read the plugs to judge the overall state of tune since you do not
want to go lean under power.
Regards,
Bill Eastman
61 MGA
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