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Old 05-26-2011, 10:36 PM   #1
teddythemachete
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Default 1982 Yamaha Virago 750 needs help

Any advise would be appreciated

Heres my situation, I have purchased a 1982 Yamaha Virago. I bought the bike for what i thought was a good price it seemed to be in mechanically good shape 12000 km. The bike was actually his wifes and she would barely drove it, maybe a handful of times a season. It has a new battery, starter, and had after market exhaust. I drove it home and it was fine except he didn't tell me that one of the pit****s leaked when its in the ON position and the bike wasn't running. When i went to start it spit oil and gas everywhere and in this process i blew the clutch oil seal. I replaced the seal and did an oil change. once that was done the bike only seemed to want to run on the rear piston, so i pulled the plugs to check what condition my condition was in. to my surprise he had two different spark plugs so i replaced those and new NGK boots. I fired her up and she was good for a few minutes then i noticed it was spitting gas out of the exhaust and then it went back to only firing on one piston at idol (upon giving it gas the second piston would fire). I figured it was my carb so pulled that apart and cleaned her up nice although she wasn't too bad. After i reinstalled the carborator I fired her up and both pistons seem to be firing but it back fires like crazy. I tried disconnecting the air mixture valve under the gas tank on left side, it seemed to run alot better but at around 3000 rpms im still getting backfiring.

Do i have a vacume problem
Is my jets still clogged
Is it my air mixture valve
Is it my after market exhaust

I tried tuning the carbs but it didnt help much, Ive sprayed the intake in carb cleaner and let it soak over night to see if that might help.

LIke I said any suggestions will be considered and greatly appreciated!


I am not goin to lie this is my first bike but ive got my auto mechanic certificate and have worked on engines of all sorts since i was 15, not only that I have been working under the close eye of my uncle which is a retired gold wing mechanic.


THanks again

Ted
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Old 05-27-2011, 06:12 AM   #2
Morbo the Destroyer
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Spraying the carb won't clear it. You need to pull it off, disassemble it, soak it in a bowl or small bucket of carb cleaner, and then clear every jet and orfice by hand. Get a gasket/o-ring kit for it and reassemble. You'll need instructions on how to set it up for the first crank (like: "turn mixture screw 3.5 turns from closed).
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Old 05-27-2011, 08:44 AM   #3
Easy Rider 2
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Quote:
Originally Posted by teddythemachete View Post
Any advise would be appreciated

but ive got my auto mechanic certificate and have worked on engines of all sorts since i was 15, not only that I have been working under the close eye of my uncle which is a retired gold wing mechanic.
I can't imagine that any advice you get here is going to be better than what you already have onsite, since "we" can't see, hear and feel what is really going on.

Depending on exactly what you mean by "backfire" you could be having a timing problem or a valve problem.......in addition to possibly still having a carb problem. Really hard to say without being there.

If you are doing this recent testing with the air filter off, that in itself can cause a lean condition and popping on decel.
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Old 05-27-2011, 10:52 AM   #4
Sir_Angus
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I'm not saying this IS your problem, but ...

80's era Viragos (especially the bigger displacements) had a problem with the heads warping. A telltale sign is if one of your pipes is bluing. Just something to keep in mind.

Best of luck!
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Old 05-27-2011, 05:00 PM   #5
teddythemachete
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Thanks guys,

still no luck, i Soaked all the carb parts in carb cleaner again today then did a BANG up job drying it and reassembling it. Now the bike only wanted to seem to want to fire on the rear piston again. I pulled the plugs to test for a arc both pistons seemed to spark although neither of them seemed to be a big blue arc as described in the manual. when i pulled the front plug the bike started but when i pulled the rear the bike would not start, gasoline just seeped out of the exhaust. As for the head I dont seem to have any blue on my exhaust pipe so im goin to hope thats not the case.

Is it possible to swap the coil packs to check if it makes any difference on the front cylinder to get igniton?

It sounds to me im getting way too much fuel and not enough spark to ignite it. I would only consider myself a armature mechanic so i didnt adjust the pilot screw or any fuel screws as described in the manual.

Any suggestions on trouble shooting to narrow down the problem would greatly appreciated, and again thanks for your current imput

Ted
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