Yamaha XV920 Virago Troubles

Reader Contribution by Keith Fellenstein
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Yamaha XV920 Virago troubles

Q: I have a 1983
Yamaha XV920 Virago. Two weeks ago, I over-revved the engine, and it ran just
fine for the next 10 miles. After 10 miles I had to stop at a stoplight and the
engine stalled. When I went to start it, my starter wouldn’t engage. The
starter had been going out like Virago starters do. I replaced the starter and
it works great. Now the bike will start but will only run on the front
cylinder. My manual said I should clean the carburetors, which I did with
carburetor cleaner, and I blew everything out with compressed air. The starting
circuit was dirty, but the rest was pretty clean. Now the bike starts and runs
better, but still just on the front cylinder. What should I do? I don’t want to
throw parts at it until I get it running. Any help would be great. I use this
bike to save gas, plus I like it and miss riding it. — Bill Porter/via email

A: Since you mentioned
over-revving the engine, let’s start with some simple engine checks. Too many
times I’ve looked for complex solutions to simple problems, wasting a lot of
time in the process. The first, simplest and least expensive test is to change
your spark plugs. Sometimes a spark plug will show a spark in free air but
refuse to fire under compression due to some minor fouling. A compression test
on the cylinders could also help pinpoint the problem. Your engine in good
shape should show compression of about 135psi per cylinder, and there shouldn’t
be more than about a 20 percent difference between the cylinders. Poor
compression can indicate a blown head gasket, piston ring problems or leaky
valves. A leak down test after the compression test can further isolate low
compression to any one of those causes. BikeMaster sells a universal
compression tester kit, and you can get a leak down tester from Harbor Freight
or Pit Posse. You may be able to borrow these tools from a local auto parts
store. You also mentioned changing the starter, so check and make sure no
wiring was disturbed when you installed the starter. After that, you can
troubleshoot the rest of the ignition. You can usually test the coils with a
multimeter as a first step to determine if they are bad. Set the meter to read
ohms, disconnect the leads to the primary side of the coil, and connect the
probes to the positive and negative terminals at the coil. Your meter should
read approximately 2.7 ohms. Do the same thing testing the secondary side of
the coil, connecting one probe to the spark plug lead and the other grounded to
the coil’s negative terminal. Here the reading should be approximately 8,500
ohms. Less than that and the coil is shorted, more than that or infinity and
the coil is open. Either way it won’t produce a spark. If your coil tests OK
you’ll have to test the pickup coil and ignitor unit. The easiest location to
test the circuit is at the ignitor box under your tank. The pickup coils should
read between 124 and 186 ohms, and again, wide variance from this indicates
shorted or open circuits. On your bike, the brown/green wire is the rear
cylinder and the red/blue wire is the front cylinder. If possible, I’d swap the
coils to see if the problem moves with the coil. Also, try moving the trigger
wire and spark plug wire from the front coil to the rear coil and see if it
still won’t fire the rear cylinder. If the bike then runs on the rear cylinder
only you’ll know it’s the coil or spark plug wire. Keep at it and you’ll find
the issue. MC

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