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Secondary Spark?


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'04 R1150RT, 103K miles.


I'm trying to track down the cause of a rough running engine which is more noticable at highway speeds. I pulled the secondary spark plug wires - one at a time from each side, installed a spark plug and grounded it by holding next to the cylinder head, and then started and ran the engine.


While I see spark on both sides, one side seems to be much more pronounced than the other. A bad lead, perhaps, or am I off base with this search?


I have done a valve adjustmment, tb balance, and installed new spark plugs. I've replaced the stick coils and the fuel injectors. Not sure what to look for next.


As always, your input is greatly valued and appreciated.



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Afternoon Bud


You might just be seeing the difference in spark direction. On the lower spark plug ignition system that is a LOST SPARK type system & a continuous loop so one side spark plug sparks (+) center electrode & the other side sparks (-) center electrode.


If you remove one spark plug (& leave wire open) the other side will have much less spark.


In any case the lower plugs do little at hiway speeds so you might be chasing ghosts there.



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Yes, last month, a few thousand miles ago, I replaced the "U" tube and filter. The other hoses looked fine. I'm getting no suction upon opening the filler cap. Running with the filler cap open makes no difference.

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Smart man, Bud.

If you let us know what part of MT you're in, maybe someone in the area has a GS-911 they could put on it.

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I'm near Helena. Not many Beemer motorcycles out this way, but I'd be very grateful if someone close by has a GS-911 to let me borrow.


This is very frustrating. Time for a compression test, maybe. But of course, I don't have those tools either.

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Those other two fuel tank lines are just as susceptible to long term disintegration as the u tube. Most of the hoses that go look good on the outside. You really need to replace them as a set. DAMHIK!

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I imagine that's true, and I don't mind taking the pump out again, but how would that cause rough running?


Evening Bud


Can you explain the ROUGH RUNNING in more detail? Maybe the type of roughness can point us to something.


If you think it is fuel pressure or fuel flow related just run the bike out to top speed, if it will hit & maintain 125+mph then you have plenty of fuel flow at enough pressure.

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It's an engine vibration that is felt through the speed ranges, but more obvious when the revs are up. Just not smooth running, even in 6th gear. I've had it up to 90 with this condition, but the vibration/roughness is too much to try to push it beyond that.


It does feel like a bad stick coil, or broken wire to a stick coil, as I've had the problem in the past. However, as mentioned, I replaced the stick coils with another pair, and I've disconnected the wires to each stick coil, one side at a time, while the engine is running, and the draw down is identical on each side, and similar in return to fairly normal idle upon reconnection. Wouldn't this process be fairly conclusive to rule out a bad stick coil?



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Morning Bud


That still doesn't tell us much about the type of engine disturbance you are feeling.


The thing that stands out here is, to you, the problem seems to feel worse at higher RPM's. As a rule that isn't consistent with ignition problems. Ignition issues usually show up more at lower RPM's under high engine loading.


Can you both HEAR the disturbance in the exhaust note & FEEL the disturbance in the foot pegs/handlebars?


If you can more feel it than hear it then you are probably looking for mechanical problems like loose alternator, loose engine bolts, clutch area issues, etc.


At higher RPM's if you can more hear it in the exhaust note than feel it in chassis buzz then it is more likely firing frequency related like fueling, valve train or ign related.


Sorry for not being more specific but diagnosing a vibration disturbance over the internet is very difficult, especially with very little information about the disturbance.


Added: If your engine is overfilled with oil (above top of sight glass) you might try removing some of the oil.


While I haven't ever seen or felt it myself there have been some reports of oil overfilling on the 1100/1150 BMW boxer increasing engine vibration.



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roger 04 rt

Here are some otherl possibilities. One is insufficient fuel flow. Another is unequal fuel injector flow. And there are more possibilities too,


For fuel flow all you need to do is measure the volume of fuel returning to the tank at idle. If it's about 2 liters per minute you're good.


For injector flow, you have to send them to a lab to be tested.


It is also possible that one of your new stick coils is a problem or that its ground wire is flaky.

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I've now done the fuel pressure flow test, and there's no issue there. And as noted, I just installed "remanufactured" and flow tested fuel injectors, and there was no change in the problem.


I just borrowed a compression tester, and find 150psi on each side - unless I've done it wrong. With the engine hot, I removed the #5 fuse, disconnected the wires to the stick coils, removed the wires to the secondary spark plugs, removed the primary spark plugs, and locked the throttle fully open with the throttemiester. I then installed the compresson tester to one side and ran the starter, then did the same on the opposite side.


The brown ground wire for the left side stick coil is a bit worn looking, but I see no breaks in the wire itself, and I manipulated it while the engine is idling, and detected no variations.


Clogged exhaust perhaps? Bad motronic unit? Anybody have any ideas?





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Clogged exhaust perhaps? Bad motronic unit? Anybody have any ideas?


Afternoon Bud


That ground wire really doesn't mean much as it is basically a RFI shield ground. Some riders used to cut that brown ground wire with the thought that grounding the RFI shield would make the coil less apt to arc internally.



As far as ideas on what's wrong-- Not much to tell you there until you define in more detail what you are chasing as far as engine disturbance goes. Your problem might be mechanical or might be runability-- from this far away we can't tell much on that without more info from you.



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Just back from another short trip. In addition to the unusual buzziness, I've now noticed a strange lope in the engine, at about 4K rpm plus or minus a couple hundred. With steady grip on the throttle, the engine slightly looses power, just for a half second or so at a time, one or two or three small drops in a row, then standard. Feels a bit like going over lumps in the road. Kind of an anti-surging, maybe.


Just checked the tb balance again, and it's pretty even.

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Afternoon BUD


Unless WAY out of balance TB balance has little effect at higher engine RPM's at road load.


On the lope?--that could be fueling, or spark, or ???


Possibly a spark plug or coil issue.


All the BMW 1150 boxers vibrate in the 3800-4500 RPM range (some worse than others) as the engine is inherently in-balance but the pistons are not directly across from each other so the engine goes into a rocking couple as both side pistons come to complete stop twice each revolution. That offset mass wants to twist or rock the engine as they start & stop ( just a fact of life on a non balance shaft 360° firing 2 cylinder boxer)

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