Question1981 Yamaha XV750 Virago
I've been having a problem with my Yamaha as of recently, and all that I know is that one of cylinders will stop firing after the bike has heated up.
The bike starts up fine, but after five miles of riding, one of the cylinders/plugs starts missing. When the problem starts occuring, the firing will cut in and out intermittenly, then cut out all together. There's also a lot of backfiring, so I don't think it's a carburetor problem.
If I let the bike sit for a while, the bike will start up fine, so I suspect it has to do with the engine getting hot.
I can only narrow it down to some kind of electrical problem. If you could give me any insight into the problem, I would be most appreciative. Thank you.
Sean Hofmans
AnswerHi Sean,
Sorry to keep you waiting, been busier than usual with my five jobs.
You may be right, there may be an electrical problem. I suspect one or the other (fuel/electrical). I'll let you read the following info courtesy of other Virago owners:
Fuel Gremlins Below are actual problems submitted by Virago Owners and Club members. Read through them and see which one matches your particular problem. Feel free to send-in your
problem solving experience.
Situation #1
I receive many repeat problems from Virago owners all around the world, but one of the most common scenarios goes something like this, "I just bought this great bike, a 1982 Virago with 13 actual miles on the clock, not a scratch on the bike and the owner had it since it was new."
The next statement goes something like, "The bike ran great for the first 20 miles then it started running rough and it finally quit . . . now I can't even start it. Did I get taken on this bike, did I get a lemon, or what?"
My answer is always, "Probably not."
I admit that I exaggerated in the first paragraph to make a point, but I have received similar comments that a person just bought a bike that sat in some guys garage for 5 years, jumped on the bike and started riding it without even considering what aged fuel will do to a fuel system.
First, you can almost be guaranteed that if someone had a bike sitting in a garage for that period of time, that he/she did not start it on a regular basis to keep it in good running condition. Nor would the fuel tank have been completely filled or have a stabilizer added. The fact that the tank was not filled, would allow for condensation to form in the tank. The inside of the tank would then begin to rust. Also, the fuel in the tank would tend to evaporate over a period of time and leave a sludge on the bottom of the tank.
Likewise, fuel in the carbs and in the float bowls tend to evaporate and leave sludge as well as the carb having built up some varnish from whatever amount of time the bike had been run.
Fuel in the fuel selector valve will do about the same thing. (Note: fuel selector valve does not apply to the 1000 and 1100)
Fuel in the fuel lines do so as well.
Some fuel may, at some time, have settled in the breather check valve, evaporated and caused the ball in the check valve to stick.
Now, you buy this bike, jump on it, start it up . . . it runs great . . . and you ride off into the sunset.
The sludge in the fuel lines, float bowls and fuel tank now start to congregate in all of the orifices of the carbs . . . the rust starts to flake off the inside of the tank and add to the congestion . . . the varnish in the carbs begins to flake off, the breather check valve won't allow the tank to breath and causes a vacuum !!
Bike chokes to death!!! Get the point??
Now, add to this a couple of dried out vacuum lines which operate the diaphragm in the fuel selector valve, which by the way has dried out and has cracked.
And all of a sudden, you have second thoughts about the great bike that you just bought.
Some of those older model Viragos are the most reliable bikes ever built by Yamaha and will provide you with many years of service and possibly several hundred thousand miles of riding enjoyment. But, when you buy a bike that's been sitting for a long period of time, you must take the time to thoroughly clean the carbs, fuel tank, fuel lines, fuel selector valves and breather check valve. Then check or replace the vacuum lines. Make sure the filters inside the fuel tank are also thoroughly clean and free of sediment.
You may indeed have bought yourself a JEWEL, but maybe all it needs is a little polishing (and I don't mean the chrome) before you run it.
Situation #2
Follow-up Fuel System Information
As a follow-up on the fuel system, I just received a fix submitted by Bob Ratcliffe, president of our Whitehorse Chapter in New Jersey. Seems that Bob had a fuel starvation problem with his bike and did all the above only to find that the problem was not yet solved. Here is his input:
I've heard a lot of stories about Viragos missing on one cylinder so I thought I'd throw in TWO of my own. I own an 1986 - 700 that I bought with 900 miles on it in 1988. The bike was kept in storage and clearly not ridden much. About two years after the buy and a lot of riding I experienced a total loss of power from the front cylinder while rolling down the road at the legal speed limit of course. A look at the spark plugs didn't reveal much other than the fact the front one was just a little whiter in color than the rear but not by a whole lot. I tried to start it again and it fired right up. A few weeks later, the same thing.
Now it was time to do something, I had to find if it was a fuel or a spark problem. I took a neon bulb put one of the leads under the plug cap and started the bike. The energy of the spark lit the bulb and I had a cheap visible means to see if power was present at the plug. I rode around like that for weeks until the condition reappeared. The bulb stayed lit while the cylinder lost power. I then knew it was a fuel problem.
I stripped the carbs, took them apart and cleaned house. The part I didn't like was that everything inside looked clean to begin with. On went the carbs and about a week later the miss came back.
A little lost at this point and almost as a afterthought, I took the fuel line hose from the gas tank off the carb and right into the cast section of the carb where the fuel line was connected, I shot a spray of Gummout carburetor cleaner (this was a spot I did not hit during the first cleaning when they were off). A reddish sludge ran down the side of the engine, I could hardly believe my eyes at the sight and the amount.
What had happened is, during storage, while this bike sat in the garage, the previous owner must not have treated the gas and did not keep the tank full. Rust developed at the bottom of the tank where the fuel is drawn from. The rust broke down into superfine particles that passed through the tanks filter and started building up in the area described above. At some point, it would close off fuel flow and the bowl would empty starving the bike for gas. By stopping, I allowed the bowl to fill up again and the float needle would punch a small hole in the sludge just so the process could start all over again.
I took the tank off, drained the gas and poured in as much and as many rust desolving liquids as I could and let things sit a week. Then I shook the tank, emptied the brew and blasted it with a garden hose. Lots of rust flakes spilled out. I blew the tank dry with a shop vac for a good half hour, put everything back together and have not had that problem since.
Therefore, if you have an older bike or one that may have been improperly stored, rust could have developed in the system and you may someday experience the same thing I did. Look for it, a lot of time and aggravation could be saved.
Bob Ratcliffe
Situation #3
Only on the highway. after doing 7 miles sometimes longer at about 70mph 5000 rpms I lose the front cyl. I have a few people telling me so many differnt things. I have bought a 81 tci rewired to fit my 1985 700 virago. tune up. new air sensor. $300 6 weeks in the shop and I still have the problem. Now I'm told try the pick up coil used about $90. I feel like I'm throwing money at a problem and not getting anywhere. any HELP anyone out there can give ! please send..OH yes I get off the high way... and the problem goes away. the bike runs great! any ideas on used parts? ..electronic parts no return! and when you still have the probelm.. sure does hurt!
Joe Beautz Responce:
From my experience of hearing about hundreds of these scenarios, I would say that you are barking up the wrong electrical circuit. You See, this is not an electrical problem at all, but more than likely a fuel problem. In just about every case that has been reported to me over the past 4 1/2 years, cylnder mis-fires have been a result of dirty fuel lines, dirty carbs, dirty float bowls, cracked vacuum lines not allowing the fuel control valve to provide fuel to the carb, etc.
I would suggest that you begin by reading all of the "Cylinder not firing" problems on my Problems & Fixes page first, then remove your carbs and clean them thoroughly . . . and I mean thoroughly. I just had one of our members relay his experience over the past year that he has been having the exact problem that you are having. He had a dealer clean his carbs 3 times and the problem persists. His problem was even more intermittent than what you have explained and would happen only out on the highway at high speeds. He then bought a manual, took his carbs out, stripped them down to the last little detail and found that they were filled with all kinds of crud and sediment. The sediment would only clog up the jets when the bike was at higher speed and thru vibration. By the way, his bike has run perfectly ever since he cleaned the carbs.
Sorry that you had to go thru the expense of buying new electrical parts which probably weren't needed
Writer Reply:
Just wanted to say thanks for helping me fix my bike. Your advice did IT! cleaning the carbs was the fix. I had talked to 2 differnt dealers. had 2 other bike repair shops try and fix it. All ended up saying it was a $500 module..plus labor..Yikes! you saved me big time!! The bike runs great! You can add another person to that list of people that have fixed this problem this way.
Thanks again,
Joe
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