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Old 02-23-2009, 07:33 AM   #1
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Default Buttom End tunning

How do you set your bottum end, or make sure its set correctly?? There are several ways ive heard of.. the clear it out, wait a few seconds for the motor to settle down then pinch the fuel line about a inch from the inlet and it should rev up after a count of 3, or when driving the car, after clearing it out on the straight, stop the car.. let the motor settle for a about 3 sec then count 5 and pull the trigger to make sure she pulls away clean and barely sputter.. There is also the theory of when you clear out the motor, if the idle hangs for several second, its to fat, keep leanning it until the idle stay high for about 10 plus seconds, then drop the idle...
My motor runs good, but im trying to find the best way to tune the bottum end to get the most out of my motor
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Old 02-23-2009, 07:39 AM   #2
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Paris Racing Products
Engine Tuning Tech Tips
Ron Paris Racing: 4254 Independence St. Chino, California 91710 U.S.A.
Phone: 909-4651189 / Fax: 909-4650089
E mail rparis@parisracing.com / World wide Web:
December 30, 1999 Tuning tech: carb Needle balance
We get dozens of tuning questions from around the world at Paris racing
daily, The number one questions is, were do I set my needles on the
Unfortunately there is no such thing as a definitive universal setting
for any engine!
Every application will have it’s own unique requirements, even two
IDENTICAL set ups can and most likely will have at least slightly
Please see tech tips following the article below [from our web site]
I would like to address what seems to be the # 1 mistake we encounter
in engine tuning:
Carburetor Needle balance:
It has come to our attention some racers are making the mistake of
setting the idle speed opening to wide [high idle] and setting the
end too rich!
This will give a false normal idle speed even though the speed is set
to high because it “loads up” the engine with excess fuel causing
the idle to be lower than set! The end result is a very unstable idling
engine that surges and may cut out as full throttle is applied because
the over rich bottom end can disguise a too lean TOP end setting!!!
Let’s address this a little more in depth! Idle speed opining set too
wide: It is possible too set the idle screw adjustment in to far but yet
the idle speed is not high! Even though the air regulation [carb barrel
or slide] may be set to a position that would normally equal a vary
fast idle, the idle is low because the low speed mixture adjustment is
set so rich that the engine loads up with excess fuel and the engine
goes into what’s commonly called a four cycle idle. One tell tail sign
of this is if after reving up the completely warmed up engine it tends
to idle fast for a few seconds then drops to lower idle speed. [Here we
go again with the written sound effects :-)] Something like
da..da..da..da..da..da..da..da then it drops to da….da….da….da
[if it were sheet music it would be like dropping from 8 beats per
measure to 4 beats per measure] If you start leaning the bottom end a
little at a time [then repeat the reving up and idle test] and it takes
longer before the idle drops your going in the right direction!
Eventually as you keep leaning the bottom the idle will stay to high,
now it is time to lower the idle to were it belongs by re adjusting the
idle screw! CAUTION!!!! Now that you have the idle set correctly the top
end may be too lean!!! Keep in mind the fuel does not directly enter the
cylinder area like a 4 stroke engine, it enters the crankcase area
first then is transferred or pumped up to the cylinder area by the
piston movement. Simply put, the crank case volume can hold much more
capacity than the cylinder so it takes some time to burn off the
residual fuel. In other words if the bottom end is to rich the engine
will be supplied by this residual fuel briefly and depending on the
demand you may be actually be experiencing a lean condition on the top
end that can range from: 1. Seems to run well but engine life is short
2. Seems to run well but car continues to get hotter the longer you run
to the point of overheat! 3. Seems to run ok on the bottom but sputters
starves or strains to gain rpm 4. Seems to run ok on the bottom but
when I give full throttle it cuts out or stalls [An overly rich top end
can act the same as 3 & 4 but excessive smoke and oil are usually
present with a distinct blubbering sound] There is no reason for an
engine to continually get hotter unless the tune is wrong [classic #2.
symptom] or there is a mechanical problem causing more load or drag on
the engine as the run continues. Exception Note: if the weather or track
conditions change DRAMATICLY. {Examples} A light drizzle starts and the
off road track goes from a very dry loose to high traction condition,
or during a race a rapid weather front like a ten degree change! It is
very important to fully warm up your engine, clutch and chassis before
making finale adjustments. The chassis in most applications also works
like a heat sink to the engine so it is important to fully saturate the
chassis!!! I like to start the engine at least 3 or 4 minutes before our
qualifier to get some heat in the engine. [Operate the throttle by hand
until you have radio frequency clearance] It still takes at least 2 to 3
minutes of hard running on the track to fully saturate the chassis!
There is a series of restrictions to control fuel flow at different
throttle/air flow positions called needles These are the five basic
parts of the carb to concern yourself with: 1.The slide or barrel
[regulates the amount of air to enter the engine controlled by the
servo] It simply blocks off the airflow to the engine proportional to
how far it is open or closed. 2. The idle/air speed screw [sets the
absolute minimum air the barrel/slide can control to maintain idle
speed] It simply is an adjustment screw that comes in contact with the
side at the nearly closed/idle position. 3. The high speed needle
[regulates maximum fuel flow allowed to enter engine at any throttle
position] It simply is a tapered needle that screws into the fuel flow
orifice [an adjustable restriction] This maximum fuel flow ideally is
adjusted to the correct mixture ratio for the surrounding conditions at
WIDE OPEN THROTTLE or WOT There are two more devices’ the low speed or
minimum spray bar and the mid range needle that restrict or control the
fuel further at less than full throttle. 4. The low speed needle
[regulates fuel to engine at idle] The low speed adjustment simply
restricts the flow at idle speed. If you look down the bore of the carb
you will see a long tapered needle [except for Picco torque carbs] When
the carb barrel/slide is closed the larger part or diameter portion of
the long tapered needle is inserted into the spray bar, this is
what’s adjusted when you turn the low speed/minimum adjustment. It
literally moves either the tapered needle OR spray bar farther in or
out changing the restriction independent of the barrel/side position.
This leans [more restriction] or richens [less restriction] the flow
from the spray bar at idle. NOTE: some carbs the spray bar is moved and
others the needle assembly is moved, both have the same effect. 5. The
mid range needle [regulates fuel to engine after idle and before full
fuel position. Notice as you open and close the carb the tapered needle
[mentioned above in item 4.] enters into a small tube this is called
the spray bar/jet. This spray bar is were ALL the fuel enters the
airflow stream regulated by the high speed, mid range and idle/minimum
adjustments! Normally somewhere between ½ and ¾ throttle open position
the needle is completely out of the spray bar, This is what is called
full fuel position or FFP [at this point 100% of the mixture is
controlled by the high speed needle. On many carbs the low speed and
midrange are not independently adjustable so the mid rage is a factor
of the needle taper and is engineered by the factory. On some SLIDE
carbs there is both independent spray bar and mid range needle
adjustments. CAUTION: be very careful with these type carbs!!! You can
identify them easily because there are four adjusting screws!
{Continued on page 2} Page 1 One each for the: High speed/top end
[normally sticks up some what vertical] Idle/air speed [normally a much
smaller screw entering the carb at an angle] Low speed/minimum [located
in the end of the slide OR on the opposite end of the carb body]
Midrange [also located in the end of the slide OR on the opposite end
of the carb body] Note: if there are adjustments on both the slide and
the carb body one is an adjustable mid range and the other the low
speed!!! Check with the engine manufacture before attempting to adjust
these types of carbs! It is very important not to use the mid screw to
adjust the low end by mistake; it is very easy to get the carb way out
of sync. Normally I recommend not attempting to adjust the mid range
even if your carb is so equipped, the gains are VERY small and mostly
limited to minute midrange drivability/economy changes that only the
most sophisticated driver will recognize! The negative is a carb that
is so screwed up only an expert can get it back in tune! Please note
the above descriptions will apply to 99% of the modern car carbs being
manufactured as of this writing with the exception of the Picco TORQUE
carb that use’s no mid range needle at all. It utilizes a fuel
management ramp built into the slide; the carb also has two completely
independent fuel delivery spray bars/jets. I wish I could tell every one
exactly how to tune their engine but I cannot! My hope with this
article is if I can help racers to more understand How your carb works,
all the other instructions and guides will make more sense! Best
Regards, Ron Paris Engine Tuning Tech Tips From Our Web Site: Should I
seal the carb with silicone? Many racers find this a must! [Particularly
in off road] Here are a few tips. 1} Be sure to use ONLY non-volatile
silicone [it should say oxygen sensor safe on the tube!] you can find
it at any auto parts store. 2} Use sparingly, apply a thin bead on the
carb neck just below the main carb body [even if there is an o-ring
present. Do not put it in the engine case bore or all around the carb
neck. [That would glue the carb into the engine for good!] You just
want a thin bead to squish out from between the engine case and carb
body just as you fully insert the carb. 3} After positioning the carb
were you want it tighten the pinch bolt assembly that holds the carb
very snug! Then add a dab of silicone to both ends of the pinch bolt
assembly. 4} Let fully cure before staring engine. Optimal carburetor
settings: There is no such thing with any size or brand engine that has
a predetermined optimal carb. Setting! If there were, all engines would
come without adjustments. There are many variables that must be taken
into consideration. Glow plug, fuel type and nitro, manifold type and
length, pipe type and were the pressure filing is, clutch adjustment,
gear ratios, tire size, ambient humidity, temperature and altitude etc,
etc, etc. The point I'm trying to make is no one can tell you were to
“set the Carb” only some one they’re with you can fine-tune it!
are that the directions were not followed correctly. Ideal engine
temperature: First let me say that there is no IDEAL temperature for any
engine. There are many variables that affect it; Ambient temp, fuel type
and nitro content, altitude & barometric pressure, Pipe/manifold type
and setting, clutch setting, glow-plug, gear ratio, available traction,
How hard your driving, on road or off road Etc. Etc. All information is
based on the Paris/Exergin probe; it is the only probe designed for
model engines and has worldwide patented Emisivity compensation. We
tested dozens of devices before we started working with Exergin and
introduced infrared tuning to the model industry. All of the following
conditions MUST be met before any temperature can be considered
correct, the engine is assumed to be in good shape. 1} There must be a
visible trail of smoke when accelerating from EVERY corner. 2} The idle
is stable. 3} The glow plug wire stays somewhat shiny and the coil stays
round [UN-distorted] 4} The performance is good. Picco on road average
conditions 20 to 40% nitro 205 to 230 degrees f Picco off road average
conditions 20 to 30% nitro 215 to 250 degrees f Nova on road average
conditions 20 to 40% nitro 220 to 260 degrees f Nova off road average
conditions 20 to 30% nitro 230 to 270 degrees f How to “READ” your
glow plug: OS and Turbo glow plugs go gray sooner [easier] than McCoy
plugs; this is not necessarily bad. Actually when A new plug wire just
goes slightly gray after a 5 or 10 minute hard run it means your very
close to an optimal horsepower tune, but be careful the next step is
TOO LEAN! My rule of thumb. 1} Wire and surrounding bottom of plug wet,
with like new shiny wire = rich side of optimum power 85% 2} Wire and
surrounding bottom of plug starting to dry and wire starting to gray =
Very close to optimum power 95% 3} Wire and surrounding bottom of plug
dry, wire totally gray but not distorted optimum power 100% 4} Wire and
surrounding bottom of plug dry, wire distorted = slightly lean DANGER!
5} Wire and surrounding bottom of plug dry, wire broken and distorted
or burnt up = extremely lean possible engine damage! Note: You can only
“Read” your plug in a nearly new state [Wire like new and shiny] A
gray plug can still operate well. After it has totally gone gray,
performance can start to fall off. To test just put in a new plug and
if there is no difference in performance save the gray one or put it
back in. If your engine does not feel or run right tray a new plug
before making major tune changes Effects of changing manifold to pipe
length: Rule of thumb: Longer manifold = more bottom end torque. [At the
expense of some rpm] Shorter manifold = more top end rpm [at the expense
of some torque] BUT you can go to far with either direction causing the
engine to run erratic or HOT! You must keep it in the “sweet spot”
Bottom line: there is no set length for every engine or pipe,
experiment with the length to suit your driving style or track needs.
Does it mater were you put the pressure fitting in your pipe: If
you’re talking about a single chamber pipe like the Associated or
Paris AL12T no big deal. But if you’re talking a two-chamber pipe, and
you go from one chamber to the other you will have to re tune the
engine. Even then it is not a big deal once it is tuned for that
location there is little if any performance difference. [It is all
relative to available pressure Vs needle setting] I recommend tapping
into the first chamber on two chamber pipes [the intake side] were the
pipe is at its largest diameter. The second chamber has more constant
pressure but can be more difficult to tune in high altitude or fast
changing weather conditions {Countinued on page 3} Page 2 How to shut
off you engine and stop runaways: If the engine is out of control and at
high RPM DO NOT USE YOUR HAND on the flywheel! Some guy’s flip the
car over and stick the toe of their shoe on the flywheel! I have seen
it work but 50% of the time the engine lets go before you can stop it!
The method I like is as follows: Try and hold the car down hard so the
wheels can’t spin [this may waste the clutch shoes but it is cheaper
than an engine!] Yank the body if you can’t get to the air cleaner,
then yank the air cleaner and put your finger on the carb intake. It is
kinda like handling a wild animal but it is a good method. Do not just
push your finger down on the foam air cleaner, which will suck all the
dirt into the engine! Holding a rag on the exhaust works too [if you
happen to have one handy] but, Be sure there is several layers of rag
it will take more than a few seconds to choke it And it will be HOT HOT
HOT! If the engine is idling normally, I just touch the flywheel with
the handle of an old screwdriver! Ron’s tips for healthy Fuel: I
always shake my fuel because some oil separation is common especially
with higher nitro but I mostly shake it to re oxygenate the nitro [old
habit from topfuel/funny car days] Water absorption Is the #1 reason for
“Bad” fuel! And is little affected by any nitro or oil/additive
package. The methanol is what’s so hydroscopic <Spelling? > [Water
magnet] My advice as always. 1 Never leave the bottle open any longer
than it takes to fill your fuel bulb. 2 never leave the FUEL BULB
uncapped any longer than it takes to fill the car. 3 always rinse out
you fuel bulb at the start of each day with a little fresh fuel. 4
NEVER draw fuel back into your bulb or put it back in the jug. 5 keep
your fuel out of direct sunlight and off the ground. 6 store your fuel
in a stable temperature. 7 I like to squeeze the extra air out of the
bottle before tightening the lid. 8 Some times it is handy to save some
1/2 gallon or quart bottles to transfer to as you the Gallon remember
to rinse them out with a little fresh fuel first. If you follow these
simple steps your day will never be ruined by bad fuel. Will it hurt my
engine to run it out of fuel: My opinion is if your engine was tuned
correctly, to start with it will not harm it running out of fuel! I
have done this hundreds of times with no damage even in our killer
engines. If just before running out of fuel the car was tuned: 1} Tuned
Slightly rich, it will speed up for a brief moment just before it dies
as you pass through the “Ideal performance” mixture stage. 2} Tuned
for ideal performance, it will fall off in power just before it dies as
it passes through the too lean stage. 3} Tuned too lean to start with,
it will bog down noticeably and may blow the plug as it pass though the
“way to lean you just screwed up stage”. This can cause some damage
to the piston and sleeve if the element wire breaks and falls in to the
engine. However, the brief lean moment should not hurt the bearings,
bushings, rod, crank etc. if you’re using high quality fuel
[especially a high castor blend like Bluethunder race formula] Is it ok
to switch nitro content or brands of fuel? There are many opinions on
this subject; I feel there are no problems doing either! The most
important thing is to use a good quality fuel! Personally, I break our
engines in on the same nitro we race with, but have had equally good
results either way! The only recommendation I would make is, if you do
switch brands it would not hurt to: 1} Let the engine idle a few
minutes before you go out on the track. 2} Run ½ to 1 tank of fuel on
the rich side. 3} Check your glow plug and if it looks good fine tune
and go for it. The reason I say to check the plug is that different
fuels have different oil additives and detergent packages. This may
wash away some of the built up oil deposits and platelets or bonding
agents [As the oil companies call them] and foul the plug. After a few
runs your new fuel will leave deposits of there own, some brands you
can see the residue because of its blue or red color. Other brands you
can’t see because they’re a light yellow or amber color but rest
assured it's there! It is normal to have these build-ups and it
cause’s no harm! What is the best Fuel? Blue Thunder Race Formula
[Paris/Blend] Has a High castor to synthetic ratio. Castor oil is
simply the best lube available for model engines [Alberto Picco and
Mario Rossi agree] but not all castors are the same! We use the finest
ultra Pure Triple A refined castor. Then we add a synthetic supplement
package, which includes anti foaming and rust properties. There is also
a wetting agent to aid in Lubricity and reduce storage dry out. The
fuel is manufactured with the latest high tech computer controlled
mixing equipment; using the freshest lab tested and certified USA made
nitro and methanol by the largest manufacture of model fuel in the
world. Should I use after run oil: Race Formula Blue Thunder is a high
castor blend that includes 3% Synthetic with anti gumming agents. It is
always a good idea to use some after run oil. First let the tank run
completely empty at idle until it runs out of fuel [try re-starting it
several times] Next put a few drops down the carb [open] and a few drops
down the glow Plug hole [leave the plug out and put a rag over the top
of the engine] And spin it over for 5 seconds on the starter box. Last
put a few more drops down the carb re install the glow pug and spin The
engine over 5 more seconds. That will do it! We May be releasing a after
run oil but in the meantime Marvel Mystery oil works great and can be
had at any automotive or hardware store. Other substitutes would be
automatic Trans fluid, 3in1 oil or Mineral oil from the drug store!
First, follow the after run oil instructions above! Remove the engine
from the car, you can then wash it off just be careful not to wash dirt
into the front bearing [even if it has a rubber sealed type] I brush it
off behind the flywheel then rap a strip of cloth around the crank,
“wedging” it between the front of the engine and back of the
flywheel. I then plug the carb and exhaust [be sure there is a glow plug
installed] then squirt it off with methanol or denatured alcohol [Not
Isopropyl it is 30% water] I do not recommend brake cleaner or motor
spray. Then blow of off with compressed air if you do not have
compressed air shake the engine vigorously and blow it off until dry
with a hair dryer, being careful not to get it HOT just warm to the
touch. Last I remove the strip of cloth let the engine come to ambient
temp [so there is no condensation formed inside] and put it in a zip
lock bag or re-install in your car! You can see many other useful tech
tips at the Paris web site
http://web.archive.org/web/200104290...risracing.com/ [go
to tech tips on third page] Good luck and enjoy your new Paris Racing
Engine, Ron Paris Page 3 Engine Break In And Tuning For The New and
Experienced Racer: Revised 12-30-99 Engine Break in for the for the New
Racer: I was honored when the gang at R/C Car magazine asked if I would
collaborate on a tuning article geared to the new and hobby racers! With
the continued growth of 1/10 off road and Explosion of sedan racers,
there was a need for a generic tuning guide. Well here it is, it was
very informative as written by the gang at the magazine, I simply added
a few tips and clarifications based on the hundreds of tech questions
we receive. Enjoy, -Ron How to Break In your New Engine Patience is the
secret to success! If you’ve read a few issues of this magazine,
you’ve probably noticed that we devote quite a few pages each month
to nitro-powered vehicles and accessories. Critics might say that we
prefer nitro over electric powered, but the truth is that we are simply
covering what’s going on in the R/C industry— nitro is hot at the
moment, and we’d be failing you if we didn’t provide comprehensive
coverage! Surely, one of the reasons for nitro’s popularity rests in
the quality of the engines themselves. Most of today’s engines are
manufactured to be easy to use and to maintain, and many sport-level
powerplants have been designed to be incredibly user-friendly. For
absolute novices, we still recommend electricpower over nitro, but if
you should decide to take the plunge, you’ll find that most engines
are quite easy to get running. Above all else, your success or failure
with a nitro engine depends on how well it’s been broken in—and
this is entirely up to you and the amount of patience you have. The
more time you take to properly break-in your new engine, the better it
will run. A well broken-in engine will develop more power and higher
rpm, and will run much more consistently than an engine that had been
rushed into race settings. . IT’S ALL IN THE CARB Everything that’s
needed to ensure your engine’s long life is contained in its
carburetor. Most carbs have three adjustments that you’ll need to
familiarize yourself with: The first, and most important, is the high-
speed needle setting. This needle valve controls the mixture of fuel
and air that enters the engine’s combustion chamber during high-rpm
running. More fuel in this mixture causes a “rich” condition, while
less fuel (more air) causes a “lean” condition. A richer high-speed
needle setting will actually help keep the engine running cooler as it
reduces rpm, and because there is more fuel passing through the
combustion chamber, a bit of “liquid cooling” actually takes place.
A leaner setting will allow the engine to achieve higher rpm, but will
also cause it to run hotter. A properly set high-speed needle will
provide a compromise between a cool temperature and high rpm. Needless
to say (but we’ll remind you anyway), extremes in either direction
aren’t good, but nobody ever blew up their engine by running it too
rich! Many racing engines also have a secondary needle-valve adjustment
that is used to control the engine’s low-speed fuel/air mixture. This
needle is used to adjust the way the engine makes the transition from
low to high rpm. It also helps control the fuel mixture when the engine
is idling. A low-speed needle setting that is rich will reduce throttle
response at low rpm, and may make the car sluggish coming out of tight
turns. A leaner setting will allow the engine to make more power during
low rpm operation. Many modern sport-type nitro engines have eliminated
the low-speed needle entirely. While this doesn’t allow for the
highest level of tuning for the experience racer, having one fewer
needle to fuss with does make these engines much more user-friendly to
the beginner, who only need set the high-speed needle. Finally,
there’s the idle-stop screw. Basically, this screw is used to keep
the carb’s slide or barrel from becoming totally closed (which would
stop the engine from running). A small opening of the carb allows just
enough air and fuel to mix and keep the engine running. Setting the
idle is usually done after you’ve properly set both the high- and
low-speed needles. WHERE TO BEGIN? READ THE BOOK! Before you even place
your nitro car on a starter box or yank its pull- starter, read the
instruction manual that came with your engine or car kit. Most nitro
kits’ manuals have a section that will tell you approximately where
the carburetor’s needle settings should be for initial start up. We
have found that higher-end (more expensive) engines tend to follow the
instruction’s settings more closely, which means that when the manual
says to set the high-end needle at three turns out from closed, this is
almost exactly where the engine will run best for break-in. For
sport-type engines, the needle position that allows the engine to fire
and run may be quite different from what’s recommended in the manual.
In our experience, if a sport engine won’t fire, leaning the
high-speed needle in small increments will get it going. Once the
engine fires and runs consistently, we will usually richen the needle
back to where the instructions recommend. Never run a new engine, or
even an older one, too lean! YOUR NEW ENGINE’S FIRST RUN We know that
you want to go out and do some hot laps the instant your new engine
fires to life—but don’t! The first few runs of your new engine are
critical. Once your engine starts, place the car on a stand so that its
wheels can’t touch the ground. Let the engine idle at low rpm for a
few minutes (two or three minutes will do), then shut the engine down
and let it cool. During this procedure, it’s also important that the
piston not be at the top of the cylinder while the engine is cooling.
Part of what’s taking place during break-in is that the engine’s
mating parts are being heat-cycled— they’re expanding when the
engine is hot and contracting when it cools. Heat cycling stabilizes
the metal and allows mating parts to fit better against each other.
Keeping the piston out of the upper portion of the cylinder (which is
smaller in diameter than the lower portion in order to create a better
seal during combustion) will allow the cylinder to properly contract as
it cools— without interference from the piston. To figure out where
the piston is in relation to the cylinder, just turn the flywheel—it
will become difficult to turn when the piston is at the top of the
cylinder, where the fit between the piston and cylinder is its
tightest. Just turn the flywheel until the piston is in the middle of
its “easy turning” part. Now you’re ready to lay down some
horsepower, right? Wrong! Repeat the above steps three or four more
times. YES, YOU CAN DRIVE IT NOW After you’ve heat-cycled your engine,
you can finally put it on the track. But don’t get too excited
yet—you must run it with a very rich high-speed needle setting. Some
engine experts recommend that, during break-in, the engine be set rich
enough so that it will actually four-cycle instead of two (our nitro
engines are two-cycle, which means that the fuel/air mixture is ignited
once for every two strokes of the piston). Four cycling means that the
engine is actually only firing one time for every four strokes of the
piston. In this condition, all of the unburned fuel passing through the
combustion chamber takes heat (and any tiny metal particles created
during the breaking-in process) right out to the exhaust pipe! Do you
really need to run the engine this rich? Well, the experts know their
stuff, but we have broken in dozens of new engines without actually
allowing them to four stroke. Whether or not you four-stroke your
engine during break-in is entirely up to you—just make absolutely
certain that the highspeed needle is set very rich: lots of blue smoke
should be coming from the exhaust, and the engine should sound
“blubbery.” During this procedure, it’s vital that you avoid
prolonged use of full throttle, which could strain the engine. You
should instead “blip” the throttle as you drive the car to avoid
spending too much time in one particular rpm range. Run the engine
using these settings for three or four tankfuls of fuel, allowing the
engine to cool in between runs. NOW COMES THE GOOD PART! Once you’ve
put about six to eight tanks of fuel through the engine (as outlined
above), it’s time to begin leaning the high-speed needle and making
some power! Begin by leaning the high-speed needle (by turning it
inward, or clockwise) by about one-hour (if you imagine the needle as a
clockface, one full turn of the needle would equal 12 hours). Run the
car for a minute or so, then bring it back in and lean the needle by
another one hour increment. Repeat this process until the engine begins
to achieve good rpm, but it shouldn’t be allowed to “scream”
quite yet. The engine should still be creating lots of blue smoke from
its exhaust. Before you achieve that screaming race setting, we
recommend that you run your engine for a few more tankfuls in this
“almost race” setting. Once you get the needle set to where your
engine is making good rpm, richen it (by turning the needle
counter-clockwise) by about a quarter of a turn—this is your final
setting. THE FINAL STEPS Once you’ve found a good setting for the
high-speed needle that allows the engine to make good power yet still
push plenty of blue smoke from the exhaust (especially when the car
exits a turn), it’s time to set the low-end needle and the idle-stop
screw. Most engine manufacturers recommend a specific setting for the
idle- stop screw, and they’re usually well within the ballpark. For
now, set the idlestop screw so that the engine will idle at a moderate
rpm without stalling. Bring the engine up to operating temperature by
driving it for a few minutes. Now stop the car and listen to the
engine’s idle speed. If the engine idles fast but then slows down in
just a few seconds, the low-speed needle is probably set too rich. Lean
the low-speed needle (by turning it clockwise in one-hour increments)
until, after running a few more laps, the idle stays high for about
twenty seconds or so when you stop the car. Once you’ve done this,
use the idle-stop screw to make the final adjustment of the idle speed.
For sport engines which lack a low-speed needle, the idle-stop screw is
the only method of adjusting the engine’s idle speed. For these
engines, simply turn the idle-screw clockwise to increase idle speed,
and counterclockwise to reduce the idle speed. Setting your engine’s
idle speed isn’t a contest to see how low you can get it without
stalling the engine! Your goal when setting the idle should be to allow
the engine to run at moderate rpm without the clutch being engaged
whatsoever. Your car should be able to sit at a standstill when idling.
If you have to hold the brake, the idle is too high. If you have to blip
the throttle to prevent stalling the engine, the idle it too low. ENJOY
YOUR NEW ENGINE! Nitro powered R/C vehicles can be tons of fun, or they
can cause tons of frustration. The difference between success or
failure lies with the break-in process. If you follow these steps, have
patience, and use your noggin, you’re assured of success. Rushing
through the break-in procedure or worse, forgettting it altogether, is
a recipe for disaster. Tuning your engine is the hardest part of nitro
racing. But once you’ve learned how the carburetor works, and which
screw does what, it will all become second nature. So when you’re
running your car, you’ll always know exactly what to adjust to gain
the highest level of performance possible. (sidebar) THE FOUR RULES OF
ENGINE TUNING 1. Rich is good. Blue smoke should always be coming from
the exhaust. 2. Always set the high-speed needle first 3. Never try to
tune a cold engine—wait for it to get up to operating temperature. 4.
Always begin your engine tuning from a rich high-speed needle setting.
Never start out with a lean setting. Tuning all carburetors and Engines
for the experienced racer: 1 when starting a new engine follow the set
up instructions first! Start the engine and let idle at a moderate
speed for two or three minutes. Then shut it down and let it cool for a
few minutes. Be sure the piston is not at the top. Repeat this
procedure three or four times. 2 Now run the engine on the track, making
sure the engine is rich. You should hear a “four cycle” sound. Be
sure to let off the throttle going down the straightaway once or twice
so the engine is not straining in its rich condition. Repeat this
procedure for three or four tanks of fuel, letting the engine cool
several minutes between tanks. Also, check the glow plug often. It
should look new (shiny wire that is not distorted). 3 You can now start
leaning [turn clockwise] the maximum needle a little at a time in one
hour increments [imagine the needle like the hour hand of a clock]
checking the glow plug often. [I use a glow igniter with a meter on it]
I recommend running a few more tanks a little on the rich side before
“Race tuning” When tuning for maximum performance [Race tune]
adjust until engine will reach Good RPM then open needle 1/8 to 1/4
turn. 4 set the low end or idle: 4.1 After getting top end set close,
bring model in, listen to the idle. If it is idling fast then it slows
down in a few seconds, it is probably too RICH on the bottom (minimum
spray bar). In that case, make it more lean (turn clockwise ¼ turn),
then run another lap and bring the car in again. 4.2 Repeat this
procedure until the idle stays high for at least 10 to 20 seconds; at
this point readjust the aircrew so the idle is at a moderate speed. The
wheels should not turn, and the clutch should be fully disengaged. 4.3
If you had to turn the minimum spray bar in more than two or three more
turns recheck the slide adjustment! [Picco Torque carburetor only] 5 you
may need to repeat steps 3 and 4 several times to achieve the
“perfect tune” Be patient. Tuning is the hardest part of gas racing,
and is the first secret to race winning results. If you are a beginner,
it is highly recommended that you ask your hobby shop or an experienced
modeler for help. Three last tips 1 Be sure engine is warmed up before
tuning 2 always tune from rich to lean. When in doubt, richen up the
maximum needle (top end) 3 If you have to turn minimum spray bar (low
end) in more than three to four turns from flush, it is a indication
the slide adjustment is too loose and needs resetting (Picco Torque
carburetor only). Good Racing, Ron Paris Paris racing products
Got Paint? Got MicroHoles? Got custom masks?

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Old 02-24-2009, 04:32 AM   #3
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Holy cow! I've actually read that years ago. I'm waiting around for the short version...

I believe this is one of the most confusing and difficult parts of the tune and fully believe that it's the biggest improvement I can make this coming year. And definately need to figure it out since our track is being redone from scratch and will be very tight and technical with short runups. I really need to figure out the difference between fat bottom masked by high idle and all of the other common bottom needle tuning issues we have all chased at one time. The high needle is easy, the bottom and idle relation can get you chasing your tail. I want to get that set for good acceleration and then be able to focus on my clutch this year.

Keep the advice coming!
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Old 02-24-2009, 04:43 AM   #4
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I down loaded this 2 years ago and guess what. THE man knows what he's talking about.
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Old 02-24-2009, 06:54 AM   #5
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Awesome link to the archived Paris site!

The Paris papers are right; read it; long or not it's worth it.
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Old 02-24-2009, 07:19 AM   #6
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I start with the top end needle and get it tuned in then go to the bottom end needle. Once the top end is correct dial the bottom end in to give you good acceleration. IMO a good setting is one that is lean enough to keep the engine running for at least 10 seconds without blubbering when you pull the trigger. I think you want the bottom end a bit fat and if you let it idle for 30 seconds or so it should blubber a bit when pulling the trigger but not stall. Typically with the engine up to temp letting it idle you should be able to see the temp dropping slowly as it idles down to 200F or lower.

I usually find an engine out of the box has too large of an idle gap. I think they do this purposely to aid in keeping it running during the break in period. I can usually tell when the engine has broken in as the idle will start to creep up. When that happens I close the idle gap to the right setting (0.5mm) and ensure the bottom end needle is set to maintain a good idle for at least 10 seconds.

I rarely use a temp gun anymore instead I tune mostly by sound. Even the smoke seems to be difficult to read especially when on the track. On the box I expect plenty of smoke but on the track I usually cant see much. Sound seems to be the best measure for me. Too lean sounds really high pitched like angry bees fighting inside your engine and too rich sounds blubbery and slow.
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