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Old 01-22-2013, 04:32 PM   #1
a41capt OP
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Help for a new GS rider

Ive searched the forum to the best of my ability, and haven't been able to find an answer to my question. Hopefully, you guys won't make too much fun of me!

I no newbie to bikes, I've been riding and racing all of the usuals since 1966, I am new to my lovey 2005 GS though, and I'd like to know what purpose the second set of plugs has. Recently, right after my purchase actually, I changed all the fluids, checked the valve lash, and pulled the plugs. The top plugs were a nice shade of ash grey, which leads me to believe that the injector bodies and electronics package is working as intended, but the lower plugs looked like they were made of charcoal. I was led to believe that it is normal for the lower plugs to look oily, but no one said anything about a heavy coating of unburned carbon!

When do these plugs fire, in other words are they only utilized during starting or under a heavy load, etc? Is it normal for these plugs to be so heavily carboned? Is this a condition I would notice during acceleration? Since I'm new to the BMW (as opposed to the old BSAs, Maicos, my KTM 950 Adventure, etc.), I'm not sure what kind of performance I should be expecting.

Thanks in advance for not flaming this 60 year old newbie, I look forward to the wisdom of the group!

John
Camp Verde, AZ. USA
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Old 01-22-2013, 05:16 PM   #2
tom28734
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Another recent '05 buyer

I bought a low mileage '05 last spring and, like you I did a complete service. My under-plugs were not black. I'll be watching for your replies on that question. Like you, I am old, (even older than you,) and had ridden nearly everything but a GS, Now, after 8k miles, I cannot imagine any other bike. Hope your experience is as good as mine has been.
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Old 01-22-2013, 06:15 PM   #3
Karlxx
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As far as I know, the lower plugs always fire and fire slightly after the primary plugs. Mine were not carboned up like you describe, have you checked if they are firing at all. They run of a different coil pack to the primaries with have the coils in each head. Also when I disconnect the primaries it still runs OK, not great but runs.
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Old 01-23-2013, 03:52 AM   #4
billdonna
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My '10 GS plugs are normal on top and pretty black on the bottom. Normal. Swap em top top bottom every 6000m/10,000km to even out the burn pattern.

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Old 01-23-2013, 01:13 PM   #5
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might have been overfilling oil/ running low octane. I would just monitor plug condition for awhile before getting too outta shape.

Jump in to doing a valve adjustment just to rule that out.
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Old 01-23-2013, 02:06 PM   #6
everycredit
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I pulled my plugs about two weeks ago. It runs much better (I think--hard to be objective about "feel").

My bottom plugs looked like the OEM spark plugs (well, they were OEM spark plugs, but looked liked they haven't been changed since the factory) and I have over 60k miles on the bike. They were very black. The primaries looked like normal wear (gray).

Is it normal? I hope so. I haven't had any problems with the bike, except for slight surging. Now that seems to be gone after my plug change.
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Old 01-23-2013, 03:34 PM   #7
JimVonBaden
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This is perfectly normal. The secondary plugs do not fire all the time.

Also, you can't judge the way the bike is running purely on the plugs of a lean burn modern engine.

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Old 01-23-2013, 05:35 PM   #8
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Quote:
Originally Posted by JimVonBaden View Post
The secondary plugs do not fire all the time.
Jim
Why is this, how does this work? I don’t understand it at all
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Old 01-23-2013, 05:43 PM   #9
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Originally Posted by Mudcat View Post
Why is this, how does this work? I don’t understand it at all
They fire all the time. The timing is varied in relation to the primaries. Depending on throttle position, rpm 'n stuff, they may fire at the same time as the primaries or a variable number of degrees after.
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Old 01-23-2013, 05:46 PM   #10
JimVonBaden
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Quote:
Originally Posted by Anorak View Post
They fire all the time. The timing is varied in relation to the primaries. Depending on throttle position, rpm 'n stuff, they may fire at the same time as the primaries or a variable number of degrees after.
So why do they do this, and why do the secondary plugs soot up if they fire all the time?

Oh, and can you post some proof of your ass ertion?

Jim
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Old 01-23-2013, 06:04 PM   #11
Karlxx
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If you loose both primaries the bike will still run... Right

So the secondaries must be firing all the time.
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Old 01-23-2013, 07:37 PM   #12
Anorak
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Originally Posted by JimVonBaden View Post
So why do they do this, and why do the secondary plugs soot up if they fire all the time?

Oh, and can you post some proof of your ass ertion?

Jim
Well, Jim, BMW says in the technical training manual:
Quote:
Ignition of the fuel is provided by an optimized two spark ignition system. All 4 spark plugs are independently triggered via pencil type ignition coils. From a throttle opening of 80% on up to full throttle the secondary spark plugs will be offset up to an advance angle of 60˚ after TDC. This ignition timing phase offset is continuously adjusted from part throttle to full throttle on the basis of defined characteristic maps. This in turn eliminates the performance inhibiting disadvantages of a parallel fired two spark system

In addition, this measure also prevents the creation of flame fronts which mutually inhibit one another and result in a knocking tendency at higher engine speeds. The retarded ignition in turn ensures a reliable combustion of the air/fuel mixture, also in case of a failure of the primary spark plug. A combustible A/F mixture may thus not reach the catalytic converter and possibly damage it.
The difference in the color of plugs is why you made the ass umption ( see what I did there?) that only one fires all the time? What about on the 1150 twin spark?
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Old 01-23-2013, 09:03 PM   #13
JimVonBaden
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Originally Posted by Karlxx View Post
If you loose both primaries the bike will still run... Right

So the secondaries must be firing all the time.
Barely.

Jim
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Old 01-24-2013, 01:13 AM   #14
everycredit
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Well, I'm not a mechanical engineer, but I guess the blackened secondary plugs are due to gravity?

In my defense, I took one year of physics in college.
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Old 01-24-2013, 01:57 AM   #15
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Originally Posted by Anorak View Post
They fire all the time. The timing is varied in relation to the primaries. Depending on throttle position, rpm 'n stuff, they may fire at the same time as the primaries or a variable number of degrees after.
Oh, OK, Thanks.
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