Those of you that have followed my ramblings over
the years may have noticed I always use Big Gun exhaust systems on
my bikes. Being an objective moto journalist I feel the need
to explain: Mike Young (owner of Big Gun Exhaust) is a friend of
mine. This would make folks think I have a soft spot for
their products, but quite the contrary is true. I have a
direct line to Young and if his pipes are sub par I’ll call
him at home and go toe-to-toe until I’m satisfied he
understands my concerns. In recent years, I’ve not had
to make “that” call. Big Gun has come a long way
with quality, fit and finish.
Big Gun Complete
“Signature Series” Exhaust System
Bolt it on and go, even with the stock jetting
your WR450 will rev quicker and pull harder. You will however
notice an amplified off idle hesitation due to the stock carb
settings.NOTE: Refer to your
owner’s manual if confused about any of the upgrades or
settings I recommend. Do not email me asking how to do this
stuff. If you can’t figure it out, ask questions on the
WR450F mailing list. (http://lists.off-road.com/mailman/listinfo/wr450)
Others might have had the same problem(s) and will offer
assistance.To make the WR450 run right
you need to follow the “Making it Run Right” tips from last
month. Once these upgrades are performed you’re
ready for the next step in performance.
Jetting
Throttle needle- 4th
position.
Pilot Jet- #50
Main Jet- #162
Air Screw- 3 ½ turns out (This setting
is a tad rich at 4,000 feet but still works just fine)
Pilot Jet
Main Jet
These carburetor adjustments were used with the
stock pipe without a “Cork” and they worked well from
800-4000 feet.
The Beast
Within
What really woke the blue beast up was the Big Gun
“Signature Series” race pipe. With this system
and the jetting changes the WR rev’ed against the limiter so
quick it took some getting used to. It also pulled much
harder with crisper throttle response. It was truly amazing;
in fact, we had a local pro take the project WR for a spin on the
Glen Helen national MX track.
He had nothing but praise for
the bikes performance. We did use the “Race Core”
for this test with a decibel level above 100. We also put the
“Quiet” core (96db) in and ran a few laps.
Performance seemed down a bit from what the race core put out but
that might be sociological. Sometimes louder seems
faster… Changing the core is a simple task. Pull
the end cap hex head bolts out and pull the core out. When
you do the packing will also come out of the silencer. Not to
worry though, pillow type packing is used and it stays in one
piece.
The included spark arrestor can be used with
both cores.Testing the sensitivity of the
jetting change with the Big Gun “Race” system we
subjected the WR to an elevation change of 2,500 feet up to 7,500
feet. It ran perfect until somewhere around 7,000 feet, then
it started to misbehave and sputter. Use our settings as a
baseline and work from there for your specific altitude.
Again, read your owners manual on what carburetor changes will help
with different altitudes.
Nitty Gritty
Mounting the complete Big Gun system requires a
few YZ426~450F silencer parts. I’d give you the part
numbers but Montclair Yamaha in California where I get my stuff
didn’t need any stinking part numbers and what was needed was
on the shelf. (Rubber insert, metal insert and a longer
bolt.)
We used the complete Big Gun system but the stock
Titanium head pipe could be used with new heat wrapping to make it
fit snugly.
Honestly, the weight difference is a few grams at
best. You also might have to bend the metal gasket on the
base of the head so the Big Gun head pipe crown will bolt on
evenly. This doesn’t seem to be a big
deal. Both the stock and Big Gun
exhaust systems weigh about the same. Yamaha used heavy-duty
stainless steel on the tail section of the pipe that makes it
heaver than it needs to be. Big Gun uses Aircraft grade
stainless steel with an internal ceramic coating. Big Gun has
an interesting theory behind the internal ceramic coating; hotter
exhaust gas expands faster increasing the exhaust gas speed for
more horsepower.
Big Gun
did a nice job on this exhaust system and on a scale from one to
ten I’d give it a seven and a half. The reason for not
getting a nine or better is because you have to buy some parts that
should be included.Mike Hobbs
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