pick up coil

[jeffro1954]

I think I have symptoms of a pick up coil wire problem but not sure. In neutral revs up very nice. when riding it and accelerating fast above about 3500 it seems flat/miss until about 5000 and then it takes off like a rocket. If I accelerate slower it doesn't seem to be flat/miss during the midrange described above. carbs have been cleaned, timing is right on and advance works (although I have not checked it yet with a vacuum pump). sound like it could be pick up coil? doesn't run right at midrange but upper range is normal?

1978 XS1100 all stock.

[Pat Kelly]

Could be carb diaphrams/slides.

[motoman]

Pull that left cover and watch that advance, should rotate freely IMMEDIATELY upon free-rev...if not advance unit itself may likely be gummy. At cruise in the mid if that isnt advanced enough it'll have a constant stutter. You could even check that while riding where there is NO traffic by removing that cover and while riding at a steady rpm where it runs a bit rough reach down and ever so slightly totate that a bit.......might surprise you....least you know whether that is the issue.

[jeffro1954]

Just need someone to confirm for me something that probably seems obvious. pick up wires that have insulation stripped off and showing bare wires is going to affect performance correct? the wires need to be fully covered by insulation? I have a hunch this will make a big difference.

[James England]

You shouldn't have any bare wires exposed anywhere on the bike. Thos pickup wires should be completely insulated. They move as the vaccuum advance kicks in and could easily touch something and ground eg a bolt head

[jeffro1954]

that would certainly explain under load the bike missing below 5000 rpm, and just twisting the throttle it just doesn't have much get up and go. still seems strange above 5500 it runs great. maybe I've just been lucky. at least 3 of them have bare wires showing.

[James England]

still seems strange above 5500 it runs great.

Well, no, not really... the vacuum advance makes the plate and wires move through quite a few degrees. You have 3 bare wires in there which will be twisting round and possibly one of them catches on something (eg bolt head).... the bike misfires but, as you get past that rev level and the wire drags over the eg bolt head, it stops grounding and the bike functions fine. You don't notice it on the way down unless you hold the bike at exactly the 'problem' rev level. The wires may even be touching each other as the plate rotates

[cywelchjr]

Well, no, not really... the vacuum advance makes the plate and wires move through quite a few degrees. You have 3 bare wires in there which will be twisting round and possibly one of them catches on something (eg bolt head).... the bike misfires but, as you get past that rev level and the wire drags over the eg bolt head, it stops grounding and the bike functions fine. You don't notice it on the way down unless you hold the bike at exactly the 'problem' rev level. The wires may even be touching each other as the plate rotates

This is something everybody is saying that has been bothering me. While at part throttle this may be true, at WOT this is NOT true as there is NO vacuum at that point and no vacuum advance, so no movement of that plate until until you reach a point where you get vacuum again because your reaching the end of the acceleration curve. This is like the one where it was claimed that 81 models would not need the pickup coil wires fixed cause they don't have the mechanical advance, while it's the vacuum advance that causes the problems. If one were to watch the vacuum advance plate on a chassis dyno under load, you would see no movement of the vacuum advance plate under heavy acceleration (this is by design and just like automotive units as well) as unless the is something wrong (or plumbed wrong) there is no vacuum applied to the advance system at either idle or WOT until MAYBE you hit top speed (and I don't think at WOT you would get any vacuum then either).

[jeffro1954]

I thought I was home free at first with the vacuum advance. I tested it with a vacuum guage and watching it with motor running and sure enough the plate advanced like it should, however as pointed out as the plate moves it moves the wires. It's possible I have bare wires touching each other, or a bolt or (sparking/shorting) going on as the beast's RPM's increase and then goes away at higher RPM's. My electrical skills are sub novice so I'm having a shop do it. I would love to be able to report this repair fixed my problem. Many of you who have had the pick up wire bug I"m sure are nodding your heads going "you have no idea how much better it's going to run"!! I'll let you all know.

[James England]

While at part throttle this may be true, at WOT this is NOT true as there is NO vacuum at that point and no vacuum advance

I don't think you're correct with this though. There is always some vacuum acting on the advance (unless the engine is turned off). The engine is permanently sucking as it turns, regardless of tickover or WOT. You only have to watch the vacuum advance do its job. At tickover it pulses slightly, as you open the throttle, it progressively rotates anti-clockwise and stays there if the throttle is left at that position. At higher throttle openings, it moves round that bit further and stays in position. It only moves clockwise as the throttle is reduced.

The position of the vacuum stub on Carb 2 means that, while ever the engine is running, there is vacuum.

[crazy steve]

..You only have to watch the vacuum advance do its job. At tickover it pulses slightly, as you open the throttle, it progressively rotates anti-clockwise and stays there if the throttle is left at that position. At higher throttle openings, it moves round that bit further and stays in position. It only moves clockwise as the throttle is reduced..

James, throttle position is only part of the story; a bigger part is engine load. Under no load or light load conditions, throttle openings are relatively small and you get a high vacuum on the motor side of the carb throttle plates. But open the throttle (in response to a load such as a hill or to accelerate) and that vacuum drops. At WOT with the motor at full song, you'll have little or no vacuum advance in the ignition. This can be easily demonstrated with a chassis dyno, or if you 'teed' a vacuum gauge into the line to the advance and went for ride. Do a high-gear roll-on, and you'll see the vacuum drop when you first crack the throttle, start to come back up as you gain speed, then drop off again as wind resistance increases load.

That's why there's two types of advance; mechanical (or now mostly electronic; the weights-and-springs are all pretty much gone) and vacuum. The vacuum advance is there for one reason, and one reason only; to promote fuel economy. If you bumped your static timing slightly (say, 5-7 degrees) and disconnected the vacuum source, you would notice little or no difference in performance, but would notice the dive in mileage. Race vehicles, almost without exception, don't use any sort of vacuum advance because it never comes into play because most of their time is spent at WOT. Same thing goes for marine gasoline motors; while they don't operate at WOT, they're under continuous load and a vacuum advance will never come into play.

[motoman]

+1 Steve!......thanks for clarifying what didn't quite come across clear from me......dead-on.

[XSive Okie]

I have an additional question. Do the front wires (left of the plate) or rear wires (right of the plate) run the 1-4 coil?

[3Phase]

I have an additional question. Do the front wires (left of the plate) or rear wires (right of the plate) run the 1-4 coil?

Richard, on the XS11 the upper coil with Orange and Blue wires to the left of the plate runs 1-4; lower coil with White and Blue wires to the right of the plate runs 2-3.

The XJ has more or less the same pickup coils but they're mounted for and aft on the pickup plate instead of top and bottom. They might have a different impedance than the XS pickups and I haven't looked to see which pickup fires which coil. The only XJ engine I have was snapped in half behind the jugs so the engine and transmission are now separate units that, for some reason, won't start.

[SFSPECBIKER79]

pickup wires

mine did the same thing when i bought it missed 2 clylinders up to around 3000rpm then ran like a raped ape after that. pulled the side cover and pulled on the pick up wires and one of them streched like speggetti. used meter wires and replaced all of them inside the cover. still running fine after 3 years service.