>From: "Chris" sorry.spam.RemoveThis@problems.com
>What are the general principles ?
>What would be the wise first move ?
There's a good CV carb tuning guide at <a style='text-decoration: underline;' href="http://factorypro.com/tech/carbtun.html" target="_blank">http://factorypro.com/tech/carbtun.html</a>
But remember that factorypro is trying to teach you about *performance* tuning,
and many riders who install K&N
oval separate filters are actually doing it for styling because they have seen
somebody else's motorcycle with K&N's and thought it looked "kewl", or they
removed
an ugly plastic airbox to improve the appearance of their motorcycle without
knowing what the airbox was actually for...
Or maybe the owner just bought the K&N filters because they were cheaper than
the original equipment filters, who knows for sure?
Airboxes actually help to improve the midrange torque curve of the engine, so
it's best to leave the airbox on the motorcycle, especially on a four-cylinder
engine with a 4-into-1 header...
>What should I be doing in the carbs ?
Learn to understand what the jet sizes mean. A #100 round main jet has a hole
in it that is exactly 1 millimeter in diameter. A #200 mainjet would have a
hole that is 2 millimeters in diameters. A #40 idle jet has a hole in it that
is 0.40 millimeters in diameter, etc...
Often a shade tree mechanic thinks that he has built a really radically
modified motor and that he needs to drastically increase fuel flow, so he runs
out and rashly buys a bunch of, say, #135 main jets to replace his #110
mainjets...
He thinks that the #135's will flow about 1/3 more fuel than the #110's, but he
is wrong, the larger jets will flow more than twice as much gas because of the
increase in area of the hole, according to the formula, area = pi times the
radius squared, so his engine winds up puffing out a lot of black soot when it
clears itself out, after stumbling a lot...
>What would be the wise first move ?
Learn all about how CV carbs work. They mostly run on the *idle jets* while you
are cruising down the road with the throttle open about 1/8th of a turn.
There's no point in screwing around with main jets or raising and lowering the
needles if the engine is rarely run with enough throttle to get a lot of fuel
flowing the the main jets and past the needles...
>Up one mainjet size ?
Maybe you might want to go up one or two mainjet sizes after you see what
effect you get out of turning the idle screws out about 1 or 2 turns after
drilling out the EPA plugs that are supposed to keep you from "tampering" with
your carbs...
>Needle up .... needle down ?
CV carburetor needles are often rather short and fat and don't taper much, so
moving the needles up to richen the mixture doesn't do a lot...
And, a lot of needles don't even have any other slots to move the clips into in
order to raise them, you have to find some small washers to put under the
needle clips to raise them at all...
Remember that a CV carb has a diaphragm which raises the slide according to the
vacuum present in the carb, and when you whack the throttle wide open, the
vacuum will decrease momentarily and the slide will go down instead of up, so
you don't get the expected increase in fuel flow past the needle, it has to
come through the idle jets instead...
>I assume that with just the K&N kit , the bike will be running far too lean
Maybe...
Learn to really *read* your spark plugs and train your ear to hear pinging
caused by mixture leaness...
Pinging sounds like you have a loose valve, and you hear the tinkling sound of
pinging when the engine is really hot, but not when the engine is cold. Loose
valves would be really noisy when the engine is cold...
If your spark plugs show little black specks like pepper burned onto the nose
of the insulator, that is the result of preignition cause by leaness, or
advanced ignition timing or the wrong octane fuel...
If you look down the spark plug holes of an engine that has been pinging, you
might see a bare aluminum spot directly under the spark plug where the carbon
has been actually consumed as fuel...
If you see shiny little aluminum balls melted onto the insulators of your
plugs, the fire in your cylinders is so hot, it is melting the tops of your
pistons...
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