Carb stuff
How many times do you hear that if you get a pipe or hi flow air filter you need to rejet your carbs? For starters, many of the hi flow air filters in an airbox don't flow as much as OEM filters in an airbox. Next little tidbit is that stock carbs usually have a rich main jet. What needs to be changed is the Idle speed mixture and the needle hieght (the float height should be fine). Carbs have basically 3 systems: the low speed, the mid, and wide open.
Low speed: this is also your idle circuit, it operates from idle until the throttle is just cracked open. (This is usually lean in stock settings for emissions), you can simply turn out a couple turns of the idle mix screw to clean this up.You can really feel this if it's out, when you roll on out of a corner at the apex or are cruising with the throttle just cracked ,it burbles and/or hesitates a little bit.
Mid: this is the bit that operates from 1/4 throttle to nearly full throttle. this is done with a tapered needle that is lifted out of the main jet exposing more of the opening the higher it is lifted. If you are lean in the mid range you take out the needle and move the circlip down one notch, then try again.
Full throttle: this is entirely the main jet's job, the needle is fully out of the way.If you feel the bike surging at high rpm then you may be too lean. The best way to tell is with a plug chop (go full throttle in top gear for 10 seconds and then cut the ignition and pull the clutch, then check the plug. not recommended practice downtown!)
If the plug has a whitish ash on the electrode it is very lean, if black it is rich. The perfect color should be a light chocolate on the porcelain part of the electrode (down in the hole) you can also get a rough estimate by looking at the exhaust pipe, if it is grey inside before the muffler you are about right, if you are grey at the tip of the exhaust you are pretty close.
For a color chart, go to the extreme bottom of this page. (it's worth it)
You can do a quick check of the idle and needle settings by slowly raising the rpms while the bike is parked, if there is any burbling or missing then that area needs to be richened or leaned.
For those poor buggers with fuel injection: go buy a laptop, a pc3, and go surf for maps! make sure you get a map that fits your exact pipe,air filter,velocity stack,airbox,and bike!
Octane schmoctane! guess what? most of the time lower octane fuel is actually better than high octane fuel! The higher the octane number the slower the burn. This is needed for high compression because the flame spreads quicker with more compression, and can work more like an explosion than a flame front and may blow away the protective gas layer on the piston causing the piston to burn. If you are going to take advantage of really high octane fuel you have to retard your spark timing to account for the slower flame spread. Lower octane burns quicker so if you have a larger motor this may be the best way to get a complete burn all the way across the wide piston. Basically for max power you want to use the lowest octane that you can get away with. This doesn't take in consideration any differences in the quality of the fuel
Speaking of velocity stacks, wanna know how they work? Every time the intake valve opens it gulps a block of air, if the stack is longer it takes longer to get the air into the combustion chamber, it works at low speed because the timing is right, as the timing speeds up the stack needs to get shorter.
Or to put it techy speak:
Shape
The exponential curve associated with the bell-mouth-shaped opening reduces
turbulence associated with air moving along the interior surface. As has already
been mentioned, this shape allows the air to flow more smoothly along the
boundary layer, which is defined as the transitional area between flowing
and stagnant air molecules.
So, the first thing learned is that the shape of the stack, when compared to a straight tube of similar length (this is important), has less turbulence, thus less kinetic energy loss, which ultimately means less horsepower loss to the rear wheel. The reason I mention ‘as compared to a straight tube’ is because no tube, or a similarly shaped shorter tube, will have less resistance to air flow.
Length
Air moves through the carburetors/throttle-bodies in ‘blocks’, rather
than a smooth continuum of flow. The reason for this is because of piston
and valve dynamics. When the intake valves open, the air accelerates through
the carburetor/throttle-body throat and flows into the combustion chamber.
The kinetic energy associated with the attained velocity helps to excite the
mix in the chamber, which then promotes more efficient combustion. When the
intake valve closes the air must then rapidly decelerate. This deceleration
creates a compression of the ‘blocked’ intake charge and manifests
itself as a pressurization, traveling at about the speed of sound, which then
moves back up the carburetor/throttle body throat, defined as the ‘front’
of a pressure wave. Once the wave-front reaches the end of the velocity stack,
rather than continuing out the stack and into the airbox, it ‘sees’
the end of the stack as a blocked path, and reverses it’s direction of
travel and moves back down the carburetor/throttle-body throat as a negative
pressure wave (vacuum wave). So as to aid the incoming charge, it would be
beneficial to time this vacuum ‘pulse’ so as to coincide with the
valve opening. The length of the velocity stack determines this coincidence.
In general, a relatively short stack aids high engine rpm performance and
a longer stack then aids lower rpm operation.
or, in fairyland, carbs work like this:
The basic secret of carb function is that inside each carb are
thousands of tiny gnomes; each with a small bucket. As you open the
throttle, more of these gnomes are allowed out of their house and into
the float bowl, where they fill the buckets and climb up the carb's
passages to the intake, where they empty their buckets into the air
stream.
But, if you don't ride the bike for a while, bad things can
happen.
Tiny bats take up residence in the chambers of the carb, and before
long the passages are plugged up with guano. This creates a gnome
traffic jam, and so not enough bucketfuls of fuel can get to the
engine. If it gets bad enough, the gnomes simply give up and go take
a nap. The engine won't run at all at this point. Sometimes you'll
have a single dedicated gnome still on the job, which is why the bike
will occasionally fire as the gnome tosses his lone bucket load down
the intake.
There has been some research into using tiny dwarves in modern
carbs.
The advantage is that unlike gnomes, dwarves are miners and can often
re-open a clogged passage. Unfortunately, dwarves have a natural fear
of earthquakes, as any miner should. In recent tests, the engine
vibrations caused the dwarves to evacuate the Harley Davidson test
vehicle and make a beeline for the nearest BMW dealership. Sadly,
BMW's are fuel injected and so the poor dwarves met an unfortunate end
in the rollers of a Bosch fuel pump.
Other carb problems can also occur. If the level of fuel in
the float
bowl rises too high, it will wipe out the Section 8 gnome housing in
the lower parts of the carb. The more affluent gnomes build their
homes in the diaphragm chamber, and so are unaffected. This is why
the bike is said to be "running rich".
If the fuel bowl level drops, then the gnomes have to walk farther
to
get a bucketful of fuel. This means less fuel gets to the engine.
Because the gnomes get quite a workout from this additional distance,
this condition is known as "running lean".
The use of the device known only as the 'choke' has finally
been
banned by PETG (People for the Ethical Treatment of Gnomes) and
replaced by a new carb circuit that simply allows more gnomes to carry
fuel at once when the engine needs to start or warm up. In the
interests of decorum, I prefer not to explain how the 'choke'
operated. You would rather not know anyway.
Eddie lawson came from the california flattracks to be a 4 time 500cc gp champion.He started roadracing a 250 before getting picked up by the kawasaki superbike team. He won the '81 and '82 AMA superbike championships before going to Europe to ride as Kenny Roberts' teammate on the Yamaha YZR500. He won the '84,'86,'88,and the'89 500cc world championships. He switched from Yamaha to Honda and won back to back championships(the only other rider to do that is Val Rossi) He then rode for Cagiva giving them their first win and several podiums. He also won the '85 and '93 Daytona 200s for Yamaha as well as the Suzuka 8 hour race
Spark plug color chart
Normal
Combustion deposits are slight and not heavy enough to cause any detrimental
effect on engine performance. Note the brown to greyish tan color, and minimal
amount of electrode erosion which clearly indicates the plug is in the correct
heat range and has been operating in a "healthy" engine.
Mechanical Damage
May be caused by a foreign object that has accidentally entered the combustion
chamber. When this condition is discovered, check the other cylinders to prevent
a recurrence, since it is possible for a small object to "travel"
from one cylinder to another where a large degree of valve overlap exists.
This condition may also be due to improper reach spark plugs that permit the
piston to touch or collide with the firing end.
Oil Fouled
Too much oil is entering the combustion chamber. This is often caused by piston
rings or cylinder walls that are badly worn. Oil may also be pulled into the
chamber because of excessive clearance in the valve stem guides. If the PCV
valve is plugged or inoperative it can cause a build-up of crankcase pressure
which can force oil and oil vapors past the rings and valve guides into the
combustion chamber.
Overheated
A clean, white insulator firing tip and/or excessive electrode erosion indicates
this spark plug condition. k This is often caused by over advanced ignition,
timing, poor engine cooling system efficiency (scale, stoppages, low level),
a very lean air/fuel mixture, or a leaking intake manifold. When these conditions
prevail, even a plug of the correct heat range will overheat.
Insulator Glazing
Glazing appears as a yellowish, varnish-like color. This condition indicates
that spark plug temperatures have risen suddenly during a hard, fast acceleration
period. As a result, normal combustion deposits do not have an opportunity
to "fluff-off" as they normally do. Instead, they melt to form a
conductive coating and misfire will occur.
Pre-Ignition
Usually one or a combination of several engine operating conditions are the
prime causes of pre-ignition. It may originate from glowing combustion chamber
deposits, hot spots in the combustion chamber due to poor control of engine
heat, cross-firing (electrical induction between spark plug wires), or the
plug heat range is too high for the engine or its operating conditions.
Gap Bridging
Rarely occurs in automotive engines, however, this condition is caused by
similar conditions that produce splash fouling. Combustion deposits thrown
loose may lodge between the electrodes, causing a dead short and misfire.
Fluffy materials that accumulate on the side electrode may melt to bridge
the gap when the engine is suddenly put under a heavy load.
Splash Fouled
Appears as "spotted" deposits on the firing tip of the insulator
and often occurs after a long delayed tune-up. By-products of combustion may
loosen suddenly when normal combustion temperatures are restored. During hard
acceleration these materials shed from the piston crown or valve heads, and
are thrown against the hot insulator surface.
Detonation
This form of abnormal combustion has fractured the insulator core nose of
the plug. The explosion that occurs in this situation apples extreme pressures
on internal engine components. Prime causes include ignition time advanced
too far, lean air/fuel mixtures, and insufficient octane rating of the gasoline.
Ash Fouled
A build-up of combustion deposits stemming primarily from the burning of oil
and/or fuel additives during normal combustion ... normally non-conductive.
When heavier deposits are allowed to accumulate over a longer mileage period,
they can "mask" the spark, resulting in a plug misfire condition.
Carbon Fouled
Soft, black, sooty deposits easily identify this plug condition. This is most
often caused by an over-rich, air/fuel mixture.
Check for a sticking choke, clogged air cleaner, or a carburetor problem -
float level high, defective needle or seat, etc.
This may also be attributed to weak ignition voltage, an inoperative preheating
system (carburetor intake air), or extremely low cylinder compression.
Worn
This plug has served its useful life and should be replaced. The voltage required
to fire the plug has approximately doubled and will continue to increase with
additional miles of travel. Even higher voltage requirements, as much as 100%
above normal, may occur when the engine is quickly accelerated. Poor engine
performance and a loss in fuel economy are traits of a worn spark
SOURCE: Champion Spark Plugs