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2-stroke performance tips, Motocross race engines, ceramic coated pistons, porting, boring, complete engine service, Motorcycles for sale.
The following Hop - up Tips are for reference only. All work should
be performed by experienced mechanics only.
We are not responsible for any work performed outside of our shop.
Due to the nature of racing engines any alterations to factory specs can decrease the life of the engine.
Never attempt to increase the performance of any engine unless it is in excellent mechanical condition.
The best time to do performance increases is at the time of a rebuild.
Before buying any parts or doing any modification you need to determine exactly what you want from your engine.
See tuning guide
Starting with the ones that are free and easy
- Clean the air filter - Sounds stupid, but you can be sure there
are a lot of bikes at the races with expensive racing parts and a dirty
air filter. The difference in power between a dirty and clean filter
is probably more than the difference in power between a stock and aftermarket
pipe. The amount of air an engine breathes is directly proportional
to the amount of horsepower it makes. Some bikes will benefit from enlarging
the air passages in the air box, or even cutting more openings. Be careful
not to cut openings that will allow mud to get splashed onto the filter.
- Less Weight - A Titanium bolt kit costs about $800. and will
knock off about 1 pound. Or you could get the same weight savings from
running 20 ounces less gas in your tank. If your running scrambles or
enduros you need a full tank to avoid making more pit stops, but for
motocross there's no reason to fill up for a 15 minute moto. Time the
moto's where you race then keep track of how much gas you use on practice
day for that amount of time. The difference in weight between a full
tank and enough to run one moto will probably be about 10 pounds. Reducing
weight at the fuel tank makes the bike less top heavy also.
- Cool Fuel - Keep your fuel can in the shade, better yet, pack
your fuel can in ice. (You can use the empty cooler since you and your
friends drank all the beer the night before). As fuel vaporizes in the
carburetor it has a cooling effect on the incoming air. Cooler air is
denser and has more oxygen, the cooler the fuel is when it vaporizes
the cooler the air will be and the more power it will make, plus the
engine will run cooler also. In drag racing it is common practice to
run the fuel line through a canister full of ice. Also the fastest drag
race times are run on cold days because of the denser air.
- Race Coolant - Racing coolants are more efficient than the
standard 50/50 mix of antifreeze and water. There is an alternative
to expensive racing coolant. Straight water cools better than antifreeze,
but it does boil at a lower temperature, and it doesn't protect the
aluminum and magnesium from corrosion. Use a mixture of 80/20 distilled
water to antifreeze (do not use tap water because the minerals in it
cause corrosion) and add Nalco to prevent corrosion. If Nalco is not
available at your local auto parts store then check at a truck parts
dealer, it is used commonly in trucks to prevent corrosion (follow the
instructions for how much to add per gallon). This mixture will cool
better than 50/50 and still protect from boil over and corrosion. You
can also add a "wetting agent" such as "Red Line". Wetting agents cause
the coolant to flow closer to the metal, they have the opposite effect
that wax has on water (beading).
- Pipes An aftermarket pipe is one of the most popular performance
modifications. When choosing a pipe be sure to keep in mind that although
some pipes can increase power all through the powerband, in most cases
the power is just moved from one rpm range to another. A top end pipe
will usually sacrifice low or mid range power in order to get more top
end, and a low end pipe will usually sacrifice top end power. Compare
dyno charts for different pipes to determine which pipe will give you
power where you need it.
Check the inside of the pipe for carbon build up or rough weld's at
the end where it attaches to the head. Remove rough welds with a die
grinder then polish with a sanding wheel. Polishing this area of the
pipe is like polishing the exhaust port. Polishing will increase power
and help prevent carbon buildup.
Make sure there are no leaks where the pipe attaches to the head. Leaks
are annoying and they cause a lose of power. Replace the O-ring, if
it still leaks apply silicone sealer around the pipe flange. For more
about pipes click here--->. How
expansion chambers work
- Reeds Reed valves also are designed to improve power at certain
RPM ranges. Stiffer reeds are for top-end power (less floating at high
RPM's) and softer reeds are for low-end (open easier and breathe better
at low end ). You can replace the reed pedals only or replace the entire
reed cage. I recommend replacing the entire reed cage. Most stock and
replacement reeds are made of carbon fiber. Older bikes had fiberglass
or steel reeds. Carbon fiber reeds can increase power in low and top
end because the lighter material can open and close faster without the
high tension needed to prevent floating with steel or fiberglass. Make
sure that the reed valves are closing completely, you will see light
through the reed cage if the reeds are not closing completely
- Ceramic Coated Piston - Thermal coating the piston dome and
cylinder head helps keep the heat in the cylinder where horsepower is
made. The thermal barrier also makes the piston run cooler for longer
piston life and less chance of seizing or burning a piston. Ceramic
coated pistons have been in use for years, in drag racing, snowmobile
racing, circle track and even NASCAR. All motors benefit from Ceramic
coating the piston, head and valves, but 2 stroke motors gain the most.
The exhaust valve is the hottest part in a 4 stroke motor and the most
likely part to fail. In a 2 stroke the piston and exhaust port do the
job of the exhaust valve, that's why 2 strokes are so prone to piston
burning and seizing where 4 strokes are prone to burning exhaust valves.
The ceramic/metalic compound protects the piston in 2 ways. It has a
higher melting point and since it does not conduct heat as well as aluminum
it acts as a thermal barrier (insulator). More heat in the combustion
chamber will generate more horsepower.
- Compression - Increasing compression will gain power all through
the powerband. The head can be resurfaced to remove material which will
increase compression. Measurements must be taken to determine piston
to head clearance before removing material. Higher compression will
raise cylinder pressure and temperature. Too much compression will cause
overheating, detonation and possible piston failure. C.C. the head before
and after machining to determine the compression ratio. See C.C.
ing the head.
- Squishbands - The area of the head where the piston to head
clearance is the closest is called the "squish band". As the piston
approaches T.D.C. the fuel/air mixture is "squished" out of this area
and toward the center of the combustion chamber. The turbulance caused
by the squish band causes the fuel/air mixture to mix with the unburnt
exhaust gases and burn more efficiently. By decreasing this clearance
the squish band can be made more efficient. The minimum clearance for
most bikes is .020" To check the clearance remove the head and place
a 1/4" long piece of solder on the outer edge of the piston (above the
wrist pin and on both sides, to keep even pressure and to avoid piston
"rocking" in the cylinder) , apply some grease to keep it in place.
Install the head and turn the engine over by hand using a wrench on
the flywheel bolt. Remove the head then measure the solder with a micrometer.
Surface the head to remove enough material to bring this clearance closer
or to a minimum of .020" Be sure not to remove too much material or
the compression will be too high and could cause engine damage. In most
cases you will only remove .010" to .040". Do not remove more than .040"
unless you C.C. the head before machining, then machine the combustion
area of the head to bring the head volume back to stock.
- "C.C. ing the head" is done by placing a piece of Plexiglas
over the head (Drill a small hole in the Plexiglas). Put grease or vaseline
on the head gasket surface to prevent leaks. Use a syringe (or any measuring
device marked in c.c.'s) and fill the head chamber with water. (don't
forget to put a spark plug in the head)! This will give you the stock
volume of the head. Mill the head to the desired squish band thickness
then open up the combustion chamber to bring the compression back down
to the stock or preferred c.c.'s.
- Power valves - Power valve to piston clearance can be reduced,
which will increase the effect of the power valve, which increases low-end
power. There are many different power valve designs and each has a slightly
different area to modify to change the clearance. Check the factory
recommended clearance. You can decrease this clearance from factory
specs but it will require periodic checks to be sure wear in the linkage
does not bring the valve in contact with the piston.
- Porting-Back in the 70's "Porting" actually meant grinding
the ports larger. This also changes the port timing. Making the ports
wider does not change the port timing but grinding the top of the exhaust
or transfer ports does. Altering the port timing changes the RPM were
the powerband occurs. Intake ports were increased in diameter, combined
with a larger carb. On piston port motors the intake timing was altered
by removing material from the bottom of the piston skirt or grinding
material from the bottom of the intake port. Exhaust ports were widened
and exhaust timing altered by grinding on the top of the exhaust port.
These changes improved top end power at the expense of low end power.
On modern moto-cross bikes the factory has done a real good job of determining
the size and location of the ports. They have spend a lot of time with
high tech equipment: dynamometers, flow benches etc. There's little
chance of improving the stock port timing by experimenting, since altering
the port timing usually requires altering many other specs to work properly
with the new port timing such as: Pipe dimensions, ignition timing,
carb jetting, compression ratio etc. Since the factory mass produces
the motors, they don't have time to smooth out the port surfaces or
to make sure the ports are located exactly where maximum performance
is reached. Today most "cylinder porting" jobs consist of just
cleaning up the casting flaws in the stock cylinder. Some other porting
mods are: "Case matching the ports" which involves matching the
transfer ports in the cylinder with the transfer port cutouts in the
engine cases (This requires completely disassembling the bottom end).
And "degreeing the ports"or "port mapping". "Port mapping"
involves placing a degree wheel on the crankshaft, rotating the crank
to the exact port timing (stock or altered timing) and marking the cylinder
by spraying bluing dye and scribing a line on the cylinder at the top
of the piston. Then the ports are ground to the scribe line. If the
ports are already higher than the scribe marks then the base of the
cylinder with have to be machined to lower the ports. An easy way to
change port timing slightly is to use a thinner or thicker cylinder
base gasket. A thicker gasket will raise the ports which increases exhaust
port timing. This will give more top end and less low end. The same
thickness should be removed from the cylinder head to keep the compression
the same as stock. A thinner gasket will decrease exhaust timing which
will give less top end and more low and midrange power. Piston to head
clearance should be checked to be sure there is at least .020" inch
clearance. For piston to head clearance see Squishbands.
- Fuels- Some common misconceptions about race fuel are: 1.
It burns hotter and can cause your motor to overheat 2. It will
give your motor more power. 1. Race fuel is a high Octane fuel.
Octane is a reference number that tells how much heat the fuel will
withstand before detonating without a spark. Octane itself is a fuel
similar to gasoline, it was given a rating of 100 to use a reference
point to compare to gasoline. The amount of heat produced by a fuel
is measured in B.T.U.'s. All gasoline's produce about the same amount
of heat so race fuel will not cause your motor to overheat, in fact
in most cases it will run cooler (race gas has additives that increase
the cooling effect it has when it evaporates, like the cooling effect
rubbing alcohol has on your skin). If high octane fuel was more likely
to do engine damage they wouldn't use it in aircraft engines 2.
Every engine requires a slightly different minimum octane to operate
properly. If your motor requires 91 octane and your using 93 octane
then it probably wont gain much from 108 or 114 octane race fuel. Most
race fuels will require rejetting because the fuel carries more oxygen
than pump gas, without rejetting it's possible that your engine will
run leaner and produce less power. So why pay more for race gas? High
octane race gas allows you to build an engine with higher compression,
more spark advance or leaner fuel mixture, without detonating the fuel.
The power advantages of race fuel come mostly from these changes. The
higher oxygen content means you will run bigger carb jets to get the
correct fuel mixture. Your engine will burn more fuel because it has
more oxygen available to burn the fuel. Octane is just one of many specifications
of race fuel. The specs of race fuel are measured and adjusted to the
legal limits according to racing organizations. Every gallon is check
and will be the same every time you buy fuel (if the fuel is fresh).
Pump gas can vary greatly from one week to the next or from one station
to another, and they only check samples of pump gas from thousands of
gallons they produce. Different additives are added to pump gas according
to the time of year and location where it will be used. In winter they
add more alcohol to help remove moisture and they use additives to make
the gas evaporate better at low temperatures ("vapor temperature").
Gas that will be used in very hot climates is given additives to lower
"Vapor Pressure" to prevent "vapor lock". This is great for your car
(especially fuel injected cars that measure and adjust fuel mixture
electronically) but for a race bike it can alter your carb jetting from
one tank of gas to another. The main thing to remember is to check carb
jetting if you run race fuel, also remember if your going to go back
to pump gas you may have to switch the jets back. In most cases stock
2 strokes run well on premium pump gas with the proper carb jetting
and will gain little from race gas. Unless your building an all out
"race only" motor I suggest using premium pump gas or mixing one gallon
of race gas to 3 or 4 gallons of pump gas. Whichever you choose you
should use it consistently
- Carb Jetting -Each thing that you change will effect the carb
jetting. It is not possible to tell you exactly what jets to run. Carb
jetting is time consuming but dollar for dollar will pay off in performance
more than any part you can buy.
Here's some instructions for jetting a carb:
Start with the jetting already in the carb or to be safe on a rebuilt
motor or big bore kit start with about 2 sizes bigger on the main jet..
Always warm up the motor by riding it, do not warm up the motor by revving
the motor excessivly in neutral. On 2-strokes use a quallity synthetic
2-stroke racing oil and jet the carb with the same oil that you will
be using. On a new motor- Break the motor in for at least an hour. The
only thing you need to do for breakin is not over-heat or over-rev the
motor, wide open is ok for short periods, just normal riding. Start
out running it easy and progressively run it harder. A new piston will
run slightly hotter because it does not have any carbon to slow heat
transfer into the piston, also new rings will allow some blow-by which
causes the piston to run hotter. Do not add extra oil to the gas or
do anything different. Extra oil changes the fuel mixture. If you are
going to use race fuel, pump fuel or a mixture of the two use that fuel
while jetting the carb. Most race fuels contain more oxygen than pump
gas and will cause the motor to run lean. Jet the carb with the fuel
and oil you will normally run. Be sure you have a clean air filter,
the condition of the filter greatly effects the carb jetting. Do not
over-oil the filter excess oil will cause the motor to run too rich.
Try to jet the carb on a day when the weather is closest to the same
weather conditions when you are doing most of your riding or racing.
Find an area where you can run the bike or quad safely on a long straightaway.
#1. Start with a warm motor and install a clean spark plug (sometimes
a new plug is harder to read than a plug with some carbon on it)or just
remove the plug and take note of the color (black, gray, white). Start
the motor and run it at wide open throttle, run through several gears
at wide open, then pull in the clutch and hit the kill button. Remove
the plug and check the color, white is too lean and black is to rich,
(you want a light to dark shade of gray) The plug will usually be lighter
in color toward the center electrode and darker toward the outer edges.
This will give you a reading of the fuel mixture at wide open throttle
(main Jet). The idea is to let the motor run at wide open and avoid
part throttle or idleing which will change the plug reading. If the
plug is to white install a larger main jet, if its to dark install a
smaller main jet. Go back to #1. If the plug color is a light shade
of gray, its good. Dark at the outer edges is OK.
#2 Run the motor at part throttle (1/4 to 1/2) as much as possible,
try to avoid idling or wide open. Shut the motor off and pull the plug.
Check the plug color as in step #1, If the plug is to dark, lower the
needle (moving the clip up, lowers the needle) If the plug is to light,
raise the needle (moving the clip down, raises the needle) If you end
up with the clip at the top or bottom groove and still not jetted right
you might have to go to a different needle(richer-thinner or leaner-fatter).
Usually the stock will work
#3 Run the motor at a normal idle speed. Turn the air mixture screw
in until you can notice the RPM's going lower, back the screw out until
the RPM,s are highest, if you go to far out the screw will have no effect,
try to find the point where it idles the fastest but the screw is not
out so far that theres no effect. When you have the right setting, a
half turn in will slow the RPM but a half turn out will have little
or no effect. Now shut the motor off and turn the air screw in until
it stops (gently tighten so as not to damage the air screw seat) It
should take about one and a half to 2 turns. If it takes less than 1
½ turns the pilot jet (slow jet) is to small ( try a larger pilot
jet). more than 2 turns and the pilot jet is to big ( try a smaller
Some other indications of carb jetting are:
1. If the motor takes an excessively long time to warm up (hesitates
until it is hot) its a sign that its running lean. Also power may seam
to fade when it gets hot, and popping sound at high RPM's
2. If the motor runs good when its cold (very little hesitation at start
up) , its a sign that its running rich, after warm up the engine will
studder and run rough or load up and foul plugs often, when too rich
- check back later more tips will be added
Do you race MX, SX, enduro's, trail ride?
What is your riding ability, beginner, novice, "A" class rider or pro ?
Regardless of riding ability if you only trail and pleasure ride you probably should concentrate on modifications that improve rideability and that do not decrease reliability.
Increased low end power will make your bike easier to handle, less chance of stalling at lower rpm's and smoother power delivery.
If your a pro running Supercross, you will want to tune for maximum top end power.
Use this as a general guide to help determine what you should be tuning for.
Your weight, riding ability, bike size, and type of riding all have an effect
- Top-end Power - All pro's.
"A" class riders in 125 MX or SX.
some 250 "A" riders
- Mid and top end power - Pro and "A" class enduro's
"A" class riders in 250 MX, or SX.
"B" class 125's MX or SX.
some "B" class 250 riders
some "C" class 125 riders
- Mid-range power - "B" and "C" class enduro's
"B" class riders in 250 MX, or SX.
"C" class 125's MX or SX.
- Low end Power - Trail riding, beginner enduro or MX
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