Author P.O.L. Mafia Date Tue Aug 15, 2006 9:47 am Type Type 1
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Category Tech Tips
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Virago Juice
Over the years I have seen some pretty common issues throughout the bike world and I have seen some bike or make specific issues. One issue that has plagued the Virago, (and all Yamaha V twins) is spark and electrical issues. Over the years I have seen a pattern that has emerged, and while looking for the root cause I have uncovered some common problems. First and foremost, a bike charging system is weak at best. Comparing it to a car is like comparing apples to oranges. A car system uses a pulley and the mechanical advantage of a smaller driven than drive pulley to speed up the armature rotation. This means that even at idle, the armature is spinning (on most) 4 times faster than the engine. On a bike, there is no such setup, your armature is spinning at crank speed, so the charging system is not producing near as much as it needs to. Older model BMW bikes are very prone to this. This is one of the prime reasons that a bike battery does not last as long as a car. On average a bike battery should be replaced every year.
Because the bike charging system, at idle, is so lacking, (especially on older bikes) that means that what makes your bike run, the TCI has to produce a spark with less juice. If you look at the V Twin from Yamaha, regardless of which one, you will notice that there is a common problem with the older bikes.
Common complaint number 1.
“Front cylinder does not fire until you get up in the RPM, or it warms up.”
Let’s look at what is going on. One, you have a weak charging system to begin with. Two, you have the rev limiter on the front cylinder so there is some extra resistance on that line. Three, the cylinder is cold which makes it harder for the spark to jump across the gap of the plug. Four, if your battery is over 1 year old, you have a weak battery. We have already addressed one so let’s look at two.
Do to the short stroke and carb design of the standard Japanese bike; very high revs are not uncommon. It is not uncommon to see 12000 RPM redlines. The engine is capable of much higher RPM but with factory parts you must have a way of stopping the rev so as to not over rev the engine and sling it apart. To do this the bike makers use a rev limiter’s to keep from over revving the engine. This is done by cutting off the spark to a cylinder at a given RPM. On the Virago this happens to be the front cylinder. There is extra resistance on the front cylinder on the TCI side of the circuit which makes it harder to fire at below rev limits. If have an improperly gapped plug or an over rich condition, this problem is compounded.
Three, it is a known fact that it is easier for a plug to fire in a hot chamber than a cold so that should be self explanatory.
Four, your battery could show good on tests but be on the low side. This will cause the charging system to have to send more charge to the battery robbing an already taxed system at idle further compounding the above issues.
Now that you know the issues, here are some tips to help the bike instead of hurt.
1. Insure your battery is in good order. Electrolytes toped off, clean (a dirty battery will discharge quickly), and is not over 1 to 2 years old.
2. Use a good quality plug, with the proper gap. Some plugs are more finicky than others in a low voltage environment, I prefer Bosh Platinum, opinions vary.
3. Keep your carb’s tuned, they don’t have to be “Spot On” but a chunk of charcoal on the insulator is not good.
4. Check your charging system every year, as the bike gets older so does the parts that run it.
5. If you add draw to the system at idle, like that new fancy light bar, expect to be replacing that battery more often.