Tech Tips for 1981-1983 Yamaha 750 Virago

A cutaway drawing of the Virago I got when I bought it.
Cutaway drawing of the 1981-1983 Yamaha Virago

Mixture Control Valve

Does your Virago run like shit? Does it smell rich? Does it start easily, but not while hot? Sounds like a Mixture Control Valve to me. This little expensive doodad lives up under the black cover just below the headstock on the left side of the bike. It controls the mixture at idle and does some other stuff. It really messes up the vacuum system when it goes bonk. It costs about $60.00 from the dealer and if it was the problem, will make your bike run straight again. What a relief. It’s relatively easy to replace, too. Just unhook it from the tab that holds it in place, disconnect the vacuum lines and reconnect the new one. Vroom, off you go…

Starting Problems

Now I’ll be the first to tell you that the starters are the Achilles' heel of these early Viragos (’81-83), but this really isn’t any good reason not to get one. That is unless you’re mortified of looking like an idiot in the eyes of your pals with smooth starting bikes. Buy one of these lovely bikes and rename it Graunch or something. Don’t miss out on a cool bike.

OK, what to do: This little trick will work on most of these Viragos. Some people will tell you to shim the starter. Most Viragos have been shimmed to death. I’ve done work on three of these bikes and in one case, I had to remove a few shims because there were too many. So, here goes….

The problem is a bad design. Any rocket scientist will tell you that. The fix is a relatively easy one and won’t cost too much. I shouldn’t call it a fix as it really isn’t a cure. It will just help your bike start much faster by getting it spinning faster and more reliably. Here’s what to do. Drain your bike’s oil. Get a piece of cardboard and then remove all the screws holding the left side engine cover on. You’ll need an Allen wrench. Do yourself a favor and buy an Allen socket for this one. As you remove the Allen head screws, stick them through the cardboard in the order that they appear on the side of the motor. They vary in length and this will help you keep them straight. When the screws are all out, remove the engine cover. Be careful as there are at least two gears that are held in place on short shafts seated in this cover. Tilt the bike away from you or place something soft under the bike to catch these things before they hit the ground. You’ll also be fighting the magnets in the alternator assembly and a couple of locating dowels. DO NOT use a screwdriver to separate the cover from the motor unless you really dig oil leaks.

Once the cover is off, clean it with paper towels and put it aside for now. The culprit here is the gear that rests toward the front of the bike on a shaft that locates into the cover you just removed. You’ll see that there’s a big stinkin’ magnet just below where it sits to catch metal shavings as they come off the gear. This is pretty cheesy, but it keeps most of them from getting into your oil. Clean off this magnet and the magnetic dot on your oil drain plug (every oil change). The gear, you will see, is beveled off on the outboard side. This is the side that engages the flywheel/rotor and spins the motor. You will also see that as the shaft spins, it forces the gear into the flywheel. This is as it should be. The noise this system makes increases as the moving gear wears. Replace this gear with a new one from Yamaha and get the gasket that seals the engine side cover as well. Once you get that gear, replace it and wear the other one as a necklace or something. Be careful, it’s still pretty sharp. Install the two shafts and gears and magnet and spring and such the way they’re supposed to go back in and then replace the gasket. Put the side cover back on and put the screws back in. You’re done!

Fill the crankcase with the suggested amount of oil and start her up. Less noise, yes? Another thing you’ll need is a good battery on this bike. Less battery power means less force at the starter and more chance that gear will pop out and rattle around and cause all sorts of hell. Keep your battery healthy and replace it when necessary.

Cylinder Ring Wear

The third article here is more of a warning than anything else. With usual wear the rear cylinder’s rings are probably good for about 40-50 thousand miles. Re-ringing the Virago is pretty straight forward and can be done without splitting the cases. Due to the Virago’s pressed steel spine frame that uses the motor as a stressed member, it is very easy to get the engine out of the frame. I believe it is about 10 bolts and and electrical connections and carb boots and fuel and vacuum lines and you’re out. This article is how to tell if you need to do your rings.

You may have noticed that the paper air filter from Yamaha is about $35.00 or so. Damn spendy this. You’ll be going through a lot of these if you need new rings. What happens is that wear on the rings causes the combustion gases to blow them by. This leads to crappy looking oil and lots more atomization of droplets. These droplets escape the engine through the crankcase breather tube. This just happens to connect to the air box ahead of the air filter in the line. Lots of oil droplets will foul your filter damn quick. This will lead to your engine not breathing very well (it’s hard to suck air through an oil donut) and your bike fouling plugs and generally running like crap. It may be almost impossible to start as well.

Hey Tim, why don’t you just disconnect the breather tube? Good idea, except now YOU smell of oil every time you ride and your bike is covered in dirt attracted by the fine mist of oil on everything. Shaft drive and dirty bikes are not compatible. If you have a dirty shaftie, something’s wrong.

There’s another problem with disconnecting the breather. The stuff that comes out of there is HOT! I had a nice burn on my leg for a good long while from being kissed by the disconnected hose. Not good. If you absolutely have to run the bike in this condition, here’s a couple of hints: The pipe comes off the rear side of the rear cylinder. Fashioning some sort of catch bottle might not be a bad idea. Hide it under the seat or beside the shock or on top of the front of the swing arm. Be careful not to foul the tire. Fouling the tire is the reason I wouldn’t recommend getting a longer tube and routing it to the rear of the bike. Oil on tires is bad.

Another quick “fix” is moving to 20W50 oil. The heavier oil will not foam/atomize as readily and will cut down on the rate at which the breather fouls the filter. Removing the air filter to save money is another idea. At the point the wear on the cylinder is such that it needs new rings, not having an air filter is no big deal. There’s probably enough oil mist residue inside the frame (where the air heads after the filter) to trap some dirt anyway. Do what you must, but the only real fix for this little problem is new rings.

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