|#1: Easy Start and better gas mileage
bonus Author: cr_roger, Posted: Sun Oct 16, 2005
1:57 pm |
In 1983, when I heard for the
first time, a Japanese bike that did not sound like a lawn mower, a
1981/750 Virago with Jardine slip-ons, and after a short ride, I fell in
love with it, traded my spouse Triumph Tiger 650 on the spot, and married
the Virago. But like any marriage, after a couple of years, the problems
started. At this point you have two choices, live with them or divorce. A
lot of Virago ownerâ€™s did in fact divorce. The beloved lady gave a good
ride, but she was hard to start. So me and my friend, who has a 1983/920,
decided that the ladies would not wear us out, and that we weâ€™re gonna
have the last word. And man, having the last word with a lady, is a hell
of a decision, and getting her started on a quarter turn is also quite an
For those who are not to familiar with engine mechanics,
the basics are divided in three groups. The engine itself, the fuel and
-The engine itself is basically a pump, an compressor to
be more precise, well letâ€™s say that half itâ€™s cycle is. All it does
is suck an air/gas mixture and compresses it. So in order to duplicate our
result, the pump has to be in good working order (good compression, valves
adjusted, ect) and, of course, the starter problem must be resolved, if
you want to get her started on a quarter turn. Weâ€™ve solved that
problem, once and for all, five years ago.
-The fuel is a mixture of
air and gas at a very precise ratio. That the carburetorâ€™s job. Again
this issue has to be resolved. Your carb has to be in top shape, clean and
properly adjusted. Now I mean properly adjusted, not by ear or by feeling,
properly adjusted. We tune our carburetors electronically with a
voltmeter, there is no other way.
-The ignition is composed of a pick
up coil, a TCI box, coils and spark plugs. Their job is to ignite,
thatâ€™s why itâ€™s called ignition, the mixture that as been compressed
at a specific point in time.
So for the purpose of this topic, the
ignition is the issue. Again the basics have been dealt with. I mean your
battery is ok and the charging system is working properly. All wire have
been check and there is no corrosion on any of the multiple plastic
connections. This is very important, we are dealing here with bikes that
are anywhere from 10 to 25 years hold, that have been left outside, in the
rain, in the snow, etc. And even if you did go through all your wires and
connections last year, this is something youâ€™re gonna have to do on a
permanent basis, check all your connections regularly.
All of this
being said, weâ€™ll take for granted that the pick-up coil and TCI unit is
working fine and that the ignition coils are also in good working order.
That does not leave much hey? Well weâ€™re getting to heart of the
problem. Yes, spark plugs and wires. Some of you must have guest it, but
have done something? Well we did not take for granted that the builders of
this bike knew what they were doing. Mind you they did a great job on the
engine, but on the rest? Just take the starter as an example.
also another thing that has to be taking in account here, is the fact that
the engineering around the conception of this bike dates from the late
70â€™s. That guys is 25 years ago. There were no personal computers back
then, well maybe the Commodore 64 or the famous Atari, and who would ever
think of the idea to able to communicate worldwide at a clic of a mouse?
PART ONE: SPARK PLUG
The recommended plugs for all Viragoâ€™s
is: NGK BP7ES, the Champion equivalent is: N7YC. Now you will noticed here
that Yamaha does not recommend the BPR7ES (RN7YC) which is a RESISTOR
type. Whatâ€™s itâ€™s purpose, a resistive element (hence the term
resistor plug) is used to help reduce radio interference in most cars and
gap erosion. This resistive element (typically 10,000 ohms) changes the
initial resonance characteristics of the ignition's secondary circuit,
thereby reducing the initial high-frequency, high-current capacitive phase
(i.e., less high frequency radio noise) of the arc discharge, and as a
byproduct helps to reduce the erosion of the gap. The ensuing low
frequency, low current inductive phase of the arc is minimally or not
affected by this element. So for our Viragoâ€™s itâ€™s useless, unless you
converted your bike to a Goldwing.
The problem that we have with our
bike is closely related to the design. The newer V-twin engine use a
decompressor to ease the stress on the starting motor. By ease of stress,
I mean less current drawing from the battery, and this is THE VIRAGO
PLAGUE. Yes guys, now we are dead center on the problem. When you start
your engine, sorry I meant trying to start your engine, the starter is
pulling so much current that thereâ€™s nothing much left for the plugs,
hence the hard starting. The solution? Well read the following
What makes good ignition? Ignition occurs in a modern
automobile when an arc is struck and current flows between the electrodes
of a spark plug, or when current migrates across the conductive medium in
a surface gap plug. While that may sound simple at first, the process
becomes progressively more complicated as engineers try to optimize the
type of spark plug with the ignition system generating the required
The amount of voltage necessary to arc the electrode gap is
set by the following characteristics:
Â· The size of the gap...
arc-over voltage is roughly proportional to the gap size
air/fuel ratio within the gap... the richer the air/fuel ratio (more
gasoline vs. Air), the lower the required arc-over voltage
compression at the moment arc-over is to occur... the higher the
compression, the higher the required arc-over voltage
composition of the electrode... certain metals for all the same conditions
stated above will require less arc-over voltage than other metals. For
example, platinum requires less arc-over voltage, all other things equal,
than does steel
Â· The shape of the electrode... the sharper and more
jagged the shape, the easier it is for voltage to jump
Â· The amount
of fouling deposits trying to remove the electron flow from the arc...
more fouling deposits and lower resistance to ground pulls more energy out
of the spark gap.
While it may therefore seem desirable to lower the
required arc-over voltage, since without arc-over there is a total misfire
and no ignition, low arc-over voltage produces low spark power because
spark power is directly proportional to arc-over voltage. That is, by
doubling the required arc-over voltage, you double the instantaneous peak
spark power, and the higher the spark power, the better the ignition.
All ignition is, therefore, a balance between the requirement to have
sufficient arc-over voltage and increasing peak spark power for better,
What benefits to specialty plugs bring to this mix?
One popular specialty type is platinum plugs. The primary advantage of
these plugs, especially when used in an OEM ignition system (especially an
older system, which may not be producing as much voltage as when it was
new), is that platinum will require less arc-over voltage and therefore,
particularly in a weak ignition, allows the gap to be jumped a higher
percentage of the time.
For example, if at factory gap and with steel
electrode plugs, it requires as much as 18,000 volts five percent of the
time to jump the arc... due to the changing engine environment and running
conditions... and if the OEM only produces 17,000 volts, then it follows
that five percent of the time there would be a misfire.
Now, if one
installs platinum plugs, which may only require, say, 13,000 volts to arc,
the five percent misfiring with steel plugs would be eliminated. Since the
ignition output on OEM ignition rolls off as rpm increases, platinum plugs
in this case would allow the motor to reliably turn to higher rpm, thereby
giving and increase in performance and possibly gas mileage.
disadvantage of this method of reducing misfires is that the higher
arc-over voltage, the better the spark when it does fire. Therefore,
platinum plugs will show a performance improvement with a weak ignition
because the benefit from reducing the percentage of misfires more than
outweighs the loss from reduced spark power.
Well thatâ€™s what we
did, we started out, four years ago with NGK BP7EVX. There is also the
newer BP7EIX which Iâ€™m testing this year. Our bike are a lot easier to
start, specially when the engine is hot (with premium gas of course, but
thatâ€™s another story). Weâ€™ve tested these plugs on many other bikes
and there was always a gain in gas millage, from 10% to 20%. Now did we
encounter any problems with these plugs? Not really, but as stated before,
everything else has to be in top shape to duplicate our results. In fact
the only problem we had were some wet fouled plugs. The plug is not a
fault here. Read the following NGK tech note on this:
occur when spark plug tip temperature is insufficient to burn off carbon,
fuel, oil or other deposits.
Will cause spark to leach to metal
shell...no spark across plug gap will cause a misfire.
spark plugs must be changed...spark plugs will not fire
spark plugs can sometimes be cleaned by bringing engine up operating
Before changing fouled spark plugs, be sure to eliminate
root cause of fouling
PART TWO: THE PLUG WIRES
will be brief on this one. The carbon type wire, found on almost all
motor, were developed to reduced the radio interference in automobiles
years ago. Unless you converted, as stated before, your Virago into a
Goldwing, these wires do not help our starting problem. The solution:
steel core wire. Youâ€™re local car parts stores have that in either a kit
or by the foot, and itâ€™s usually yellow. Plus these new wire will have
the newer silicon insulation.
Gook luck, and keep the rubber on