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Glow Plug Recommendation:
The glow plug can make a big difference in how your engine performs. We recommend using a "hot" heat-range glow plug intended
specifically for performance engines like the Thunderbolt # 3 (P/N 115559) or the McCoy MC-59 (P/N 690215) during the break-in
process. After the break-in period you may want to use a medium heat-range glow plug like the McCoy MC-8 (P/N 690205). Do not
use glow plugs intended for four stroke airplane engines. Using the wrong type of glow plug will cause the engine to run erratically
and make it difficult to tune properly.
Air Filter:
The air filter is a very important part of your engine. Failure to use the air filter will damage the engine in a very short period of time. If
you are driving your vehicle in very dusty conditions, we suggest wetting the foam air filter element with after-run oil to prevent fine dust
particles from passing through the filter element.
Step 1: Breaking In the Engine
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IMPORTANT
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The XTM Racing 24.7 nitro engine is an ABC engine.
The cylinder sleeve is tapered at the top, causing severe resistance when
the piston moves through the top of the stroke. This is normal. When
the engine heats up to operating temperature, this resistance will decrease
and the proper clearance will be achieved. The break-in procedure will
guide you through the steps necessary to properly break in your new
engine. Please follow the steps closely.
The break-in process allows the engine parts to perfectly fit to each other
and properly protect each part from premature wear. The engine should
be broken in using a good quality R/C car fuel that contains no more than
20% nitromethane.
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Follow the previous procedures to fill the fuel tank and start the engine.
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Once the engine starts, keep the glow starter attached to the glow plug
and let the engine run for about 10 seconds without giving it throttle. This
will allow the engine to warm up. At this point the engine should be running
very "rich" and there should be excessive white smoke coming from the
tuned pipe. The engine will also sound like it's running rough.
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After the engine has been running for about 10 seconds, remove the
glow starter from the glow plug. Advance the throttle in short, quick bursts
and drive the truck around for about 2-3 minutes. If the engine is running
rich enough, you should notice excessive white smoke coming from the
tuned pipe and the engine should sound like it’s running very rough. Also,
the truck will barely be moving. If there is not excessive white smoke
coming from the tuned pipe, richen the high speed needle valve. After 2-3
minutes stop the engine by pinching the fuel line to the carburetor.
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Let the engine cool for approximately 10 minutes, then restart it. Set the
high speed needle valve mixture to a slightly leaner setting, about 1/8 turn
more in. Repeat the procedure above then stop the engine and let it cool
for approximately 10 minutes.
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Repeat the procedure above, while leaning the needle valve slightly more
each time. In all, you should run the engine a total of about 45 minutes.
After 45 minutes of run-time the engine will be broken in. Run the engine
with the needle valve set slightly rich, but lean enough to power the
truck adequately. At this point the engine should hold a good setting on the
high speed needle valve and you can begin to fine tune the needle valve
settings to increase performance.
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It is of the utmost importance that the engine never be
leaned out too much. When running the engine, you should always be
able to see a trail of white smoke coming from the tuned pipe. If you can’t,
stop the engine immediately and richen the high speed needle valve
mixture. You should also make sure there is plenty of air flowing over
the cylinder head to keep the engine from overheating.
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Be careful to never lean out the engine too much.
Remember that the lubricants for your engine are suspended in the fuel.
If you lean out the fuel mixture too much you will also be lowering the
amount of lubricant entering your engine. Less lubricant means more
chance of your engine overheating and possible engine failure.
Setting the High Speed Needle Valve:
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Start the engine and remove the glow starter from the glow plug, then
allow the engine to warm up for about 10 seconds.
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After the engine has warmed up, drive the truck as you normally would.
If the engine seems to be running rich, lean the high speed needle valve
about 1/16 of a turn at a time until the desired setting is achieved. Always
make sure you run the engine slightly rich - you want to be able to see a
white exhaust trail at all times.
To get more power from your engine you can use fuels containing up
to 30% nitromethane. We must caution you, though, that once you run
the engine with increased nitro you may not get satisfactory results if
you decide to go back to a lower nitro content. Also, if you use fuels
containing 30% nitro, we highly suggest adding a .10mm head gasket
(# 148418) to lower the compression ratio. If you don’t lower the
compression ratio, overheating and erratic running will likely occur.
Setting the Low Speed Needle Valve:
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Start the engine and lean out the high speed needle valve as per the
previous procedures. Close the throttle until the engine slows down enough
so that the clutch is disengaged and the wheels don’t turn when the truck is
lifted from the ground. Allow the engine to idle for about 10-15 seconds.
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While holding the truck off the ground (making sure to keep your
fingers out of the moving parts) quickly open the throttle in a short burst. If
the engine just stops running as soon as the throttle is advanced, the low
speed needle valve is too lean. With the engine stopped, richen the low
speed needle valve about 1/16 of a turn.
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Restart the engine and repeat the procedure above until the engine will
transition smoothly and quickly. Very slight hesitation in the transition is normal.
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If you quickly advance the throttle and the engine seems to be very rich
during transition (i.e., lots of smoke coming from the tuned pipe and very
rough sounding), the low speed needle valve is too rich. With the engine
stopped, lean the low speed needle valve about 1/16 of a turn.
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Restart the engine and repeat the procedure above until the engine will
transition smoothly and quickly. Very slight hesitation in the transition is normal.
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Now drive the truck as you normally would for a while to get a feel for
how the engine reacts to throttle. Now that you know the proper way to tune
the engine, you can make slight adjustments to the carburetor until you are
satisfied with the performance.
After your engine has been broken in, you can set the high and low speed
needle valves for optimum engine performance.
Step 2: Fine Tuning the Engine
