Virago foam air filter modification
The standard XV1000 & 1100 Virago air filter is not exactly free-flowing. Yamaha
have crammed a small paper element into a compact side pod that owes
more to aesthetic compromise than optimal design. Being so small for
two big cylinders, it is guaranteed to stifle the engine and clog up
pretty quickly. Yamaha replacement elements sell for a premium price.
Foaming at the mouth
If you want to escape these penalties in horsepower
and portable property, you could try fitting an aftermarket filter.
I had planned to select one of the excellent
Uni sock filters for
my bike, hoping that I might somehow modify and retain the outer pod
chrome to keep the visual balance of the bike as well as some measure
of rain and bird [poop] protection. This would have netted the ultimate
performance bonus, but I was put off by the time and effort it would
have taken to contrive this arrangement. The Virago has made me really
lazy. I expect to ride it, not fiddle with it.
So, with my fuel economy steadily worsening as the old paper element became
more and more matted and clogged, I eventually threw off my procrastination
and came up with a compromise:
The standard paper element, I've discovered, can be modified to hold a piece
of foam that offers less restriction and the advantage of multiple reuses.
Maybe it won't breathe as well as a Uni sock at 7000 rpm, but it does
mean that no other modifications to the air pod are necessary, and the
bike retains its standard appearance. Total time to complete the conversion
is about an hour or two.
Unless, that is, you don't have a suitable piece of foam rubber hanging
around (I was lucky). If not, you'll first have to find a piece from
a rubber supplier (Clark
Rubber in Australia), a hardware store, or perhaps a packing company.
I used a small sheet of ordinary density stuff that was about 11mm thick
(0.43in), but it could probably stand to be a little thicker. In fact,
next time I service it I'm thinking of making mine into a dual-element
by adding a sheet of thin stuff (~4mm) over the top which will catch
the bulk of the dirt first.
Once you've got a piece of foam, the next step is to attack your old
paper element with a pair of pliers. You want to pull off the filter
paper and most of the glue without mangling the plastic body or the
wire gauze underneath. The glue is super tough, so be firm but careful.
If you wreck the metal mesh, you should be able to source something
to replace it at the hardware store. If you've got it intact, separate
it from the paper and straighten it out. Don't worry if you have to
sacrifice a few strands on the edge to get it free from the glue. Don't
worry about residual, hairy glue that might be left on the plastic either.
As long as it's a vaguely straight surface that the foam can seal against
you'll be okay.
Now, because the foam is much floppier than thick corrugated paper, you need
to brace it to stop it from being sucked into the engine. I achieved
this with five small ribs of fencing wire running lengthwise through
the filter body. Coat-hanger wire would do nicely too. You simply drill
matching pairs of holes in the plastic end plates, thread your wire
through, and bend the wire's ends so that it can't come out. The wire
should be positioned just below where the foam will sit. In my own plastic
element body this meant drilling holes along a contour at the very edge
of the indented segments of the end plates (see photo). The metal mesh
sits directly on top of these ribs and together they make it impossible
for the foam to be sucked through into the inlet tract.
Next you can cut your piece of foam. I've provided the rough measurements
of my piece here if you want to use them as a starting point. I've deliberately
made the foam generously oversized so that when it's in place it is
actively pushing against the edges to create a seal. You have to sort
of tuck it into place. The dimensions aren't critical, but better to
err on the side of too much here.
Once it's in place, you need a system to stop it springing outwards
too. The simplest thing I could come up with in a hurry was to simply
lace it down. In the last photo you will see that I've drilled eight
holes along the very outside of the straight plastic sections. I chose
some good quality braided synthetic chord and just laced it up like
a shoe. Don't tighten it down and compress the foam too much. Just pull
Before you assemble it together for the last time, make sure that the mesh
is between the ribs and the foam and that you've oiled the foam. You
can buy special filter oil from motorcycle shops or just apply gear
oil and squeeze out the excess. Also, run a bead of grease or petroleum
jelly along the edge of the foam element and/or its mating surfaces
on the plastic to assist the seal and prevent grit from sneaking past
the foam. While you're at it, do the same for the main sealing surface
along the bottom of the plastic body—the one that bolts up to the airbox
itself. This will help the seal there too (it's a pretty slack arrangement
and can use a bit of help, especially now that you've reduced it's stiffness,
drilled holes in it, and looped string through parts of it).
Service intervals will vary with the amount of dust you encounter, but
you can usually get a fair idea of how dirty the foam is just by looking
at it. A lot of backyard mechanics think that it's a good idea to give
foam elements a final wash with detergent and water, but the people
at Uniflow say that this shortens the foam's life, and do not recommend
it. Whether this is true for all foams I don't know, but I never use
water on foam elements anyway. I use a few small consecutive washes
of mineral solvent (turps, kerosene/paraffin, petrol/gasoline all work—but the latter variant, being of the volatile, low flash-point kind
is unsafe to work with, of course
Performance and jetting
The foam element made an immediate improvement to my
bike, especially at higher revs where I could feel it pulling harder
and breathing much more freely.
However, with my aftermarket shotgun pipes, not to mention the Hitachi
carbs' lack of throttle pumps, the jetting seemed to be a fraction on
the lean side following the above treatment. It started pinging a little
when the engine was loaded heavily (such as when cracking open the throttle
in top gear when riding slowly). This occurred with ordinary Australian
unleaded which is only about 91 RON octane (or 87 octane in the
American AKI system). I decided to raise the jet needles and thus richen
up the midrange. The idle circuit seemed rich enough already (I almost
never need choke to start it) and the main jets can stay standard for
now (they don't see that much use anyway).
The Hitachi needles aren't adjustable, so I achieved the desired effect
by placing small washers underneath them. Once the carb assembly is
out of the bike (follow this
procedure) it's an easy modification. The trickiest part is finding
washers to suit. I found some of appropriate thickness and outer diameter,
but had to drill out the centres to fit the needles. At first I made
them too tight. The needles bind on the washers if the centre hole is
not large enough because the washer sits on an uneven surface. If this
happens you're likely to think that the needle is seated when it's actually
way higher than it should be (use a felt marker on the needle to double-check
your work). I ended up with a 4.5mm centre hole which lets the needle
move around nicely.
My washer was about 9.5mm in total diameter, and about 0.8mm thick.
This lifted the needle less than the equivalent of one notch of a typical
adjustable needle's increments (0.9mm).
If you've got a later model bike with Mikunis, you'll have to investigate
their needles yourself to see if they are adjustable. I suspect that
they are not, in which case you should be able to use washers also.
Try the 0.8-1.0mm thickness range as a safe starting point.
This jetting adjustment worked beautifully for me. I am very happy.
The pinging problem disappeared and the engine's grunt and responsiveness
increased quite markedly. So much so that I'd say it is a necessary
step to realising the real potential of the foam filter element. Later model Viragos with Mikuni carbs might respond differently.
In the top picture of the finished filter assembly I've pointed
out the two extra inlet holes that I've drilled in my unit to increase
airflow into the box. This barely increases intake roar at all (darn
it) but does augment the narrow standard inlet somewhat.
There's precious little free space to drill out the plastic backing
plate. I didn't want to cut the chrome outer cover, which is about the
only other alternative.* If you're really careful, you should be able
to figure out where you can place these two holes on the left side so
that they don't interfere with structural plastic. You can start with
smaller holes and gradually ream them out until you can't make them
any bigger. It all helps.
there's another way of increasing the airbox inlet area. Thanks to Jeremy
for pointing this out. He has placed washers underneath his chrome cover
mounting points so that the chrome cover no longer seals against the
main body. In fact, he has a gap of about 1/4 inch (7mm) running the whole
way around the airbox now. This allows a bit of rain to hit the filter,
but he is running a foam element also (a K&N one) which can tolerate
a bit of water better than a paper element can. Very crafty.
John "Flagman" Finn has produced a comprehensively
illustrated tutorial on adapting a Screaming Eagle / K&N paper
filter assembly to the Virago.
High-mileage Hitachi carburettor owners might like to refer
to the notes on the main page regarding carburetor synchronising.
Back to my main XV
/ Virago page.