I'm not as familiar with Webers as I am with Mikunis, but I'm getting there
as I play with mine. The idle jet probably won't make any difference that
the idle air screw can't adjust for, and it certainly won't effect
performance. Increasing the air jet size has the same effect as decreasing
the main jet but it seems to have most effect at 1/2 to 3/4 throttle. I
cured a rich popping on feathered throttle by increasing the air jet size
and decreasing the main jet. You do still have to check full throttle
mixture anytime you change either main or air jet.
I like the tunability of the Webers, but they sure have a lot of gilhickeys
to fiddle with. The good news is you can get them spot on for any engine.
The bad news is that you'll have a fortune in small brass bits by the time
you do. Concentrate on getting the full throttle mixture right, that's where
you spend most of the time in a racecar--on or off. If the engine is grossly
rich or lean, change both the main and the air jet (main sizes go up to
richen, air jets sizes go down to richen). Most weber side drafts I have
seen have the main and air jet reasonably close together in numeric size--in
other words, something like main 115, air 150 vs. main 200, air 50. I don't
know if that's universally true, it's just an observation.
I've bought every book I can find on webers and find them universally poor.
they describe the carbs throughly, but give little information about tuning.
[This message was delayed as it was in HTML format and needed to wait
for me to deal with it manually. mjb.]
|