Tune the engine following the guidelines set forth in the “Setting The Needle Valves For Optimum Performance” section of this
manual, and consider the engine temperature a secondary issue. It is OK to check your engine’s temperature, as a reference
point, but do not “temperature tune” your FR21 or FR27.
IMPORTANT: Just because the engine is designed to run up to 290º F, do not lean the primary (main) needle valve to achieve
this head temperature, unless your operating conditions dictate it! It’s OK to run the engine this temperature ONLY if the air-fuel
mixture is properly set for the operating conditions that YOU are running in. Also, don’t allow your engine to run too cool – you’re
not protecting its longevity! Operating the engine “blubbering rich” will cool the cylinder-sleeve to the point where
the piston
will begin to rub excessively in the pinch-zone, because the cylinder-sleeve is not hot enough to expand to its intended designed
operating size. The pinch-zone is that necessary area around the top of the tapered cylinder-sleeve, where the piston comes in
contact, creating the necessary seal for proper combustion chamber compression. Excessive rubbing due to under-expansion
of the cylinder-sleeve produces pinch-zone wear. Pinch-zone wear produces combustion gas blow-by when the engine is up to
normal temperature. Combustion gas blow-by produces loss of power…the number one reason that piston and cylinder-sleeve
assemblies must be replaced.
IMPORTANT: Pinch-zone wear, resulting in loss of compression, is NOT covered by warranty.
We have no control over what brand of fuel you use, and/or the way you operate your engine. Your FR21 or FR27 is built using
the latest ABC technology, and will last just as long as any other brand of ABC type engine, as long as it is used in accordance
with this instruction manual, therefore it is your responsibility to operate your engine properly, to obtain the longest usable life
possible.
The Effect of Fuel
Different fuels drastically affect the way your engine will run. One manufacturer’s 30% nitro blend isn’t necessarily the same as
another’s – there are many variables: the type of oil (synthetic or castor), the amount of oil (% in the fuel blend), the oil blend (%
synthetic, %castor), and oil quality will require a different needle valve setting for any engine. With this in mind, here are some
rules to follow when fuel-tuning your engine:
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