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I took the 850 to a bike night tonight. It ran great all the way there. After a few hours I left only to find the bike running poorly after a quick check I have lost a cylinder. Being away from home I headed to a different store for a more in depth check. When I got there the bike acted normal. I was there for about an hour and when I left the bike was once again down one cylinder. It continued to run bad all the way home with the only exception being at one or two stop signs....power came back for a few seconds and then gone again. My guess is a stuck valve? Any thoughts. I'll be trouble shooting in the morning, starting with a plug inspection and a compression test.
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It could be any of several things. What's the maintenance history of the bike? How long have you had it? What is the carburetor/air box condition and history? Exhaust? Electrical? Ignition?Originally posted by 76_Mike_82 View Post
Why do you think it's a stuck valve? That's highly unlikely.
My first guess would be a fuel delivery issue. Second would be ignition. -
My first check would be the ignition....sigpic
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I've had it for over 4 years and thousands of miles. The air box and carbs were both very good. I have been in the carbs as recently as May, lost a float valve so I changed them all back to the originals with new o-rings. I guess I am thinking valve as because of the way it went and then came back for a few seconds. Also wasn't thinking ignition as it is just one cylinder, One cold and three hot. The coils were replaced last year due to poor leads instead of replacing them I replaced the coils. As for the ignition box, is it possible to lose just one cylinder? It is an 82 with electronic ignition and two outputs one to each coil so if the box was bad I would think there would be 2 cylinders with issues not one. I could be wrong which is why I am asking. I'll see in the morning....Comment
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Also I should add there has always been a noise from the cam area on start up it normally goes away after it warms up tonight it was there still when I got to the second stop. I had looked it up before and found that most say it is the cam moving side to side which happens....true or not I didn't think much of it until it stayed tonight. I was/am planning on a long trip at the end of this month so I am hoping it's not a valve.Comment
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Your thinking is OK, but your direction is backward.Originally posted by 76_Mike_82 View Post
The box of electronics (the ignitor) does NOT output anything to the coils. All that is in that box is basically some heavy-duty transistors that take the place of points, which means that power comes from the battery, through the coils, then through the ignitor, finally to ground. Yep, the current flows from the coils to the ignitor, not from the ignitor to the coils.
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A good start is to actually know what is going on. Take a ride with a water squirt bottle and when a cylinder cuts out, spray all four and determine if one or two cylinders are not as hot as the others. Water will vaporize on a firing cylinder pipe downtube where a non-firing, if you squirt water on the cylinder downtube, will spit and sizzle. Once you know where the issue lies, you can start some intelligent troubleshooting.Comment
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Swap the plug leads around between the "suspect" cylinder and the other one on the same coil. If the problem moves to the other cylinder then you know it's plug cap / lead related. If it stays, change the spark plugs around. If it moves, then it's the spark plug. If it's still there after that then it's probably a fuelling issue.
It's good practice to rule out the easiest things first when troubleshooting these sort of problems.Current:
Z1300A5 Locomotive (swapped my Intruder for it), GS450 Cafe Project (might never finish it....), XT500 Commuter (I know - it's a Yamaha :eek:)
Past:
VL1500 Intruder (swapped for Z1300), ZX9R Streetfighter (lets face it - too fast....), 1984 GSX750EF, 1984 GSX1100EF (AKA GS1150)
And a bunch of other crap Yamahas....Comment
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Three pipes too hot to touch one I can hold... one cylinder not working not much need for a water test.
Steve thinking not backwards technically. Electron flow states electrons flow from negative to positive. But your right the ignitor box does replace the points and makes a path to ground so depending on which theory you use no not really an "output". I was taught both and either can be used as long as you stay consistent.Comment
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with just one cold cylinder, it's making me think that the plug/cap/lead is bad. if it was a coil, especially oem style coils, then 2 cylinders would be cold. and if it was a fueling issue, I would think that you would have more issues than being dead on one cylinder.Comment
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That diagnosis does make sense. That would be an easy fix, too.Originally posted by 60ratrod View PostComment
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Also makes sense when it really wakes up, even momentarily while going down the road. I think the best bet would be to get a new cap since they are so cheap, and maybe a new lead if the coils have been replaced with universal units. I chased my tail on my 81 kz cause the coils weren't up to snuff. I think i went through the carbs 7 times that summer until i took the 650g off the road and decided to try coils 1 more time (they were dyna 3 ohms).Last edited by Guest; 06-30-2016, 05:18 AM.Comment
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And just to prove a point, my kz started running rough last year, which made me take it off the road and buy my 07 vn900b. I re-replaced the throttle shaft seals & plug wires, but until i bought a 3rd set of dyna coils (which dropped one side) it felt way under powered. So i would check the plug, cap, lead, and possibly coil. Oem and universal units mostly drop both at once, but you never know. It seems i always get the oddball issuesComment
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Switching the ignition leads between the cylinder that fires and the one that doesn't on the same coil will tell you if the problem is the coil lead or the carb. Another option is a valve but that's unlikely unless you haven't kept on top of adjustment. How long since you last check them?Ed
To measure is to know.
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Update. I went ahead and checked compression while they are all on the low side the cold cylinder is one of the better ones. Inspecting the plugs the cold cylinder plug looked more oil soaked but dry(blackish not sooty) Anyway I bore scoped the the cylinder and it too looks to have oil in it. Might be un-burnt gas but definitely black. When it did kick on I could smell something but just a hint figured it was coming out the tail pipe and as I'm going down the road no chance of smelling it. You guys are slightly scaring me with this talk of a cap.... it's electronic ignition no cap. Guess I'm looking at the coil next.
Thank you for the help so far.Comment
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