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Motorcycle Firing On Back Cylinder Only

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Motorcycle Firing On Back Cylinder Only

PostAuthor: Victor_S » Tue Dec 29, 2020 5:11 pm

Hello everyone,

I've been stuck with an issue with my 1995 Virago XV535 for some months now, and I really hope that someone here can help me some with some hints about what should I do next.

If it helps, here's a short background of my bike:
I bought the bike about 3 years ago in a relatively OK condition. After a year of riding, I started to have some issues - mainly loss of power, backfires and later couldn't even start the bike.
I went to a mechanic (we don't really have moto services around here).
The guy told me that the valve train chain (hope I got the naming right) almost broke + the dog teeth on some transmission gears were worn and all of these had to be changed. Also I asked him to change the clutch and throttle cables since they were old as well. The bike stayed there about half a year.
So I got my lovely Virago back, excited to get back on the roads. Everything went smoothly (except some change in the exhaust sound - which I still cannot understand why it changed).
After a few months of riding, I left my bike in the garage for about a week. When I came back and tried to start it, it didn't want to. The engine turned over (did I say that right?), but it wouldn't fire up. Battery good, compression is good in both cylinders, spark plugs are new, good spark as well. But the front front spark plug was getting wet (too lean). So I thought it might be a carb problem. So I called another mechanic, and he managed fire it up by cleaning the spark plugs and by putting some fuel on them. Still, it managed to fire it up only with the reserve tank and the BACK cylinder only. It didn't want to start with the main tank.
So, during a day or two, he cleaned the carbs, synchronized them and changed the fuel filter.

And here's my main problem - recently got my bike from the mechanic, went to work (had some occasional backfiring, otherwise everything seemed to be fine).
After work, went to my bike, started it (with choke on - it was really cold). But while it was warming up, it started to backfire a lot. After it got warmer it stopped, but I couldn't close the choke without the bike dying out. So I had to go all the way home with the choke on. On the road, I felt some loss of power. When I finally arrived at the garage, found out that the bike was running again on one cylinder only (the back one). The exhaust from the back cylinder was really hot, while the one from the front cylinder was barely warm.
One guy suggested to check the valve clearences. Did that, almost everything OK. When I removed the exchaust tappet cover from the front cylinder - some oil dripped out (quite a lot actually and the color is really odd). Is this supposed to happen? I'll put some photos below. But in the end, same issue.

Besides that, made some calls, searched the internet and this forum, but no luck.
I just got into the mechanical part of the motorcycle and I really like it. But I am still learning and with my limited knownledge I don't think I can fix, or at least, find the cause of this issue without the help of this great community :rockon:

So, here I am, not being able to ride my beautiful bike :ssorry:

PS: This is my first post here, so I'm sorry if I made it too long. :ops:
PPS: Besides all this, I wish you happy holidays and a happy new year! :xmas:
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Re: Motorcycle Firing On Back Cylinder Only

PostAuthor: Flyingdog » Wed Dec 30, 2020 3:51 am

:VTF:

Whelp, ya gotta alot to unpack there.

Victor_S wrote:I went to a mechanic (we don't really have moto services around here).

That sure doesn't help. Just possible this maybe the first problem. Specially if he's not use to motorcycles and does just enough to get by.

Victor_S wrote:The guy told me that the valve train chain (hope I got the naming right) almost broke + the dog teeth on some transmission gears were worn and all of these had to be changed.


Almost broke? Needed to be changed? Were they? Some dog teeth not right? Not sure bout this and/or why he was that deep into the tranny. Or possibly just had the crankcase (left side) cover off and was looking at the shift barrel or something. No idea what went on. One vs. the other wouldn't effect how your describing the problem. Well, possibly the timing chain...maybe...but if it was "not" broke, highly unlikely. Unless it jumped a tooth.

You also got lotta "time differences" between when it seemingly worked vs. it didn't. Meaning, just going to take some investigating on your part to pin this down.

Without getting too deep in the weeds, I'd suggest latch'n onto a manual, bone up on some troubleshooting. At first blush, I'd also concentrate on the carbs. Meaning: if one cylinder isn't firing, the first thought would be that carb isn't getting the A/F mix, needed. (Possibly clogged pilot, main jet and/or floats not right) Why? Cuz you said you had to use the choke to keep it running (aka: starting system), meaning, having to use the choke means you were introducing "more" fuel while running. Cuz, unlike a typical choke, this system "adds extra fuel" rather than choking off "air", when choke lever is pulled "on". Not knowing "what" this mechanic did, is probly the first problem, specially for you, in tracking down why that one carb isn't working. You gotta lotta jets, passages (air/fuel) that can cause this disruption.
https://www.yamahapartshouse.com/oempar ... carburetor
https://www.yamahapartshouse.com/oempar ... /fuel-tank

Least that's on the fuel delivery side. Then, of coarse ya gotta a whole list of possibilities on the electrical side, too. Coil, wires, connections etc etc etc. But gotta go one way or the other to start with. Unfortunately, seldom is there an instant fix...specially long distance diagnosis. Unless ya gots 'just' a bad spark plug. But that doesn't happen too often.

Oh yea, you'll also get oil when taking the valve covers, off. Your pics look normal. But, about the color? Have no idea. Maybe heat related, maybe someone put some kinda oil additive in there. Super old? Diluted by gas from malfunctioning carb? Hell.. maybe someone ran transmission fluid in there. :bg: Let's hope not. People do some odd things.
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Re: Motorcycle Firing On Back Cylinder Only

PostAuthor: Cusstout 1100 » Wed Dec 30, 2020 12:18 pm

:yup: And then there's the fuel pump and controller....
My Ride, '97 XV1100, +14, 10" over forks, progressive rear, Jardine forward controls, cobra slip-ons, K&N Filter, Dyno Jet Stage 1, Kuryakin grips, heat demon heaters, custom fabricated seat, chrome side covers, bullet signals, risers, custom modified rear fender with modified FZ1 tail light, sectioned and reversed front fender, custom paint...

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Re: Motorcycle Firing On Back Cylinder Only

PostAuthor: Hellgate » Wed Dec 30, 2020 1:02 pm

Have you checked for vacuum leaks? That will often cause backfires and the bike not running well in general.
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Re: Motorcycle Firing On Back Cylinder Only

PostAuthor: mark75 » Thu Dec 31, 2020 3:38 pm

Howdy, and Welcome to VTF.

it nearly always helps to give as much info as you can. (issue, & what you've done - results)

ditto :yup:. also [in-general] - always be certain your battery is 'good': fully charged, good connections, etc.
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Any day above ground is a good day.
so Laissez les bon temps roulez. just roll safely --- Semper Vigilans --- always watchful

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Re: Motorcycle Firing On Back Cylinder Only

PostAuthor: roger64racing » Tue Jan 05, 2021 12:14 pm

I had a similar issue with my 1994 535 a few months ago and I found that it was not sparking strong enough and sometimes no spark at all on the rear cylinder, it turned out to be that the TCI unit had gone down, I rewind motorcycle stators for a living, so I thought I would have a go a repairing the TCI box. Fortunately the circuit board was not encapsulated in a resin and was easy to get access to, first I noticed a "burnt" smell and on closer inspection noticed one of the Power switching Transistors was fried also the diode and resistor underneath it looked toasty to. I replaced the damaged parts and also the same components for the front cylinder, fitted all back on my bike, hit the button and it fired up straight away on both cylinders, revs up nicely with no popping and banging.

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