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Thread: Plug to correct surging?

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  1. #1
    JohnWC
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    Plug to correct surging?

    I know this is an old topic, but bear with me. I love my '96 R1100RT, but it certainly seems to have the "surging problem". At 2500-3000 rpm, 2nd gear, holding the throttle steady, it wants to constantly go slightly up and down. The bike doesn't surge back and forth, but it isn't a steady engine output. It had Autolite Xp3923 plugs in it when I got it. Plus four used 3923s, plus two Bosch Super Plus plugs, and two new Autolite AP3923 plugs. I gather the previous owner was working on the problem. I just did a complete tuneup and put in $28.00 worth of BMW FR6DDCs. When I asked the parts person at Bob's BMW about the Autolites he was pretty curt, saying, "We don't deal with Autolites, only BMW plugs." I guess he was well aware of the problem, but didn't want to validate it.

    The bike seems to run very well now, much better since I synced the two sides. The BMW plugs seem to be nice, twin electrode plugs. And BMW does specify them for this machine. I would think they know what it is supposed to take. Should I scrap the pricey BMW plugs and put in the Autolite Platinum 3923s? Will it possibly solve the problem? Any why? What is it about the cheaper Autolites that make the machine run better than the $14 per plug BMW plugs?

  2. #2
    Benchwrenching PGlaves's Avatar
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    Quote Originally Posted by JConway607 View Post
    I know this is an old topic, but bear with me. I love my '96 R1100RT, but it certainly seems to have the "surging problem". At 2500-3000 rpm, 2nd gear, holding the throttle steady, it wants to constantly go slightly up and down. The bike doesn't surge back and forth, but it isn't a steady engine output. It had Autolite Xp3923 plugs in it when I got it. Plus four used 3923s, plus two Bosch Super Plus plugs, and two new Autolite AP3923 plugs. I gather the previous owner was working on the problem. I just did a complete tuneup and put in $28.00 worth of BMW FR6DDCs. When I asked the parts person at Bob's BMW about the Autolites he was pretty curt, saying, "We don't deal with Autolites, only BMW plugs." I guess he was well aware of the problem, but didn't want to validate it.

    The bike seems to run very well now, much better since I synced the two sides. The BMW plugs seem to be nice, twin electrode plugs. And BMW does specify them for this machine. I would think they know what it is supposed to take. Should I scrap the pricey BMW plugs and put in the Autolite Platinum 3923s? Will it possibly solve the problem? Any why? What is it about the cheaper Autolites that make the machine run better than the $14 per plug BMW plugs?
    There is enough anecdotal evidence of success with single electrode plugs that it is worth giving them a try on your specific bike. Many years ago when I was a bit of a gearhead in high school I learned about "indexing" spark plugs. It seems that when the ground electrode is between the spark and the incoming fuel charge ignition was not as crisp and complete. Indexing the spark plugs involved marking the plug, and then using slightly different thickness washers to make sure that the spark was not masked from the incoming fuel charge by the ground electrode on one side of the plug when tightened to the proper torque. We could buy indexing washers by the boxfull.

    Any old Smokey Yuninick fans from Popular Mechanics (or Popular Science, I forget)???

    BMW introduced the R1100RS with triple ground electrode plugs, and soon switched to the double ground electrode plugs. The advantage to multiple electrodes is not better ignition - you still get only one spark jump - but the voltage will find the least resistive gap. Once one electrode wears a little, the spark will pick a different one for a while. You do gain longer plug life. This was notably pointed out when Cadillac went to recommending a tuneup every 100,000 (not a typo) miles. Over the extended life of the plugs the spark will keep switching from one ground electrode to another many times.

    But simple probability says that the odds of having a shielded spark is higher with three electrodes than with one electrode. Ditto for two vs. one. That is the logic behind the single electrode plug. The 3923 just happens to be a compatible (length, thread, and heat range) plug but with some cross referencing you can find equivalents from other brands.

    Now if on your bike you happen to have a two-electrode plug with the ground electrodes perpendicular to the flow of the inrushing fuel charge, and substitute a single electrode plug which tightens with the single ground electrode masking the spark from the fuel charge you just made it worse. But probability says it will most likely be better.

    You can mark plugs and determine where the electrodes are versus the intake valves. What is hard to determine is how the fuel charge is flowing in the dynamic flow in the cylinder. But if you have a bike that surges with dual or triple electrode plugs there is a reasonable basis to see if a single electrode plug helps.
    Paul Glaves - "Big Bend", Texas U.S.A
    "The greatest challenge to any thinker is stating the problem in a way that will allow a solution." - Bertrand Russell
    http://www.bigbend.net/users/glaves

  3. #3
    JohnWC
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    Thanks, Paul. I would never have imagined that the spark shifts from one electrode to another over time. I just figured that they would both be sparking at the same time, but I guess that would not happen, as you say. Very interesting. And that does explain how you can get the long life out of them. Clever. Of course it also would suggest that an old fashioned single electrode might work better. Personally, for the cost of plugs, I'll take better performance over longer life, like most of us would. I guess I will do what the previous owner did, try the Autolites. Maybe in the future I shouldn't view factory BMW parts as the absolute best I can get. Brake pads, discs, fuel lines, etc.

  4. #4
    Registered User Bmandiego's Avatar
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    I replaced with the Bosch plugs as well. Running a combination of Seafoam and Techron, replacing the plugs, and putting new fuel lines and hoses seemed to help my surging.
    My bike -a r1100rt-p -never had a huge surging issue, it only happened at the low RPM, with a light load. Under acceleration the surge is nonexistent.
    It seems that the bike, while at the low rpm/light load area, seems to be constantly searching for a good fuel mixture.......
    2000 R1100RT-P

  5. #5
    JohnWC
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    [QUOTE
    My bike -a r1100rt-p -never had a huge surging issue, it only happened at the low RPM, with a light load. Under acceleration the surge is nonexistent.
    It seems that the bike, while at the low rpm/light load area, seems to be constantly searching for a good fuel mixture.......[/QUOTE]

    That describes mine exactly. Is this condition something that people just try to minimize as much as possible, then live with it? It's a great bike in all other aspects.
    Since it's tune up, it's been a real pleasure to ride.

  6. #6
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    surging will rarely if ever show up during accelerations. it is virtually by definition of its causation a steady-throttle condtion.
    very accurate and precise tune-up, or fuel mapping changes (chip, Power Commander, FRK or similar) help. that, or get a R11S- they have always been pretty surge free due to their particular exhaust system. RTs are the most prone to exhibit surging.
    Ride Safe, Ride Lots

  7. #7
    Benchwrenching PGlaves's Avatar
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    Quote Originally Posted by JConway607 View Post
    Thanks, Paul. I would never have imagined that the spark shifts from one electrode to another over time. I just figured that they would both be sparking at the same time, but I guess that would not happen, as you say. Very interesting. And that does explain how you can get the long life out of them. Clever. Of course it also would suggest that an old fashioned single electrode might work better. Personally, for the cost of plugs, I'll take better performance over longer life, like most of us would. I guess I will do what the previous owner did, try the Autolites. Maybe in the future I shouldn't view factory BMW parts as the absolute best I can get. Brake pads, discs, fuel lines, etc.
    I want to add a bit of history for folks who were not riding and paying attention to BMW Oilheads back in the mid-1990s. My very good friend Rob Lentini, who has passed away, was a Senior Master Sergeant in the Arizona National Guard and a civilian avionics technician with the same National Guard. Rob and Steve Aikens both had R1100RS models (as did/does my wife Voni). Voni's is a "beta bike" built in early 1993 but called a '94 model. Hers never surged and didn't even have a Cat Code Plug. Rob's did and did. Aside: Cat Code plugs are just jumpers that allow BMW to use the same main wiring harness on several models but to designate which of several fuel injection maps is correct for that specific bike/market. When the R1100RS was the only Oilhead the harness was hard wired. When the GS, and then the RT were introduced, so were Cat Code plugs. Removing the Cat Code plug just causes the Motronic 2.2 to default to richer mixture known in the automotive world as limp home mode. It is rich all across the various speed and load conditions, not just steady throttle light loads where surging happens.

    Rob had an excellent instrumentation and testing background from his avionics repair career and tested a number of things, well documenting everything he did. He tried various Cat Code plugs under various conditions. He originated the use of the 3923 spark plugs. He determined that many TPS units and throttle body idle settings weren't optimal. The TPS issue became his Zero=Zero article. He wrote about his testing and the results and posted them to the IBMWR long before BMW MOA even had a web site. I had the pleasure of working beside Rob on a few occasions at rallies when folks had "incurable" surging that Rob could make disappear. Long before the invention of the Techlusion devices or the Booster Plug Rob was the guru regarding Oilhead fuel mixture control.

    Today we hear about yanking Cat Code plugs, or resetting throttle bodies, or Zero=Zero, or using Autolite 3923 spark plugs, and many people don't know where or how those techniques came about. I would recommend that anybody who has an R1100 that surges go to the Oilhead Tech section of the IBMWR.org web site and look for anything written by Rob. It will be an eye opener. If you happen to be able to find the October and November 2008 issues of the Owners News you might like my two-part series titled Internal Combustion.
    Last edited by PGlaves; 11-12-2012 at 06:50 PM.
    Paul Glaves - "Big Bend", Texas U.S.A
    "The greatest challenge to any thinker is stating the problem in a way that will allow a solution." - Bertrand Russell
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  8. #8
    Registered User rxcrider's Avatar
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    Quote Originally Posted by PGlaves View Post
    If you happen to be able to find the October and November 2008 issues of the Owners News you might like my two-part series titled Internal Combustion.
    Someone here sent me scanned PDFs of those articles a while ago. I can pass them on to anyone else in need. Drop me a PM with your email. File size is a little under 1100 KB.

  9. #9
    Registered User roger 04 rt's Avatar
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    Quote Originally Posted by PGlaves View Post
    I want to add a bit of history for folks who were not riding and paying attention to BMW Oilheads back in the mid-1990s. My very good friend Rob Lentini, who has passed away, was a Senior Master Sergeant in the Arizona National Guard and a civilian avionics technician with the same National Guard. Rob and Steve Aikens both had R1100RS models (as did/does my wife Voni). Voni's is a "beta bike" built in early 1993 but called a '94 model. Hers never surged and didn't even have a Cat Code Plug. Rob's did and did. Aside: Cat Code plugs are just jumpers that allow BMW to use the same main wiring harness on several models but to designate which of several fuel injection maps is correct for that specific bike/market. When the R1100RS was the only Oilhead the harness was hard wired. When the GS, and then the RT were introduced, so were Cat Code plugs. Removing the Cat Code plug just causes to Motronic 2.2 to default to richer mixture known in the automotive world as limp home mode. It is rich all across the various speed and load conditions, not just steady throttle light loads where surging happens.

    Rob had an excellent instrumentation and testing background from his avionics repair career and tested a number of things, well documenting everything he did. He tried various Cat Code plugs under various conditions. He originated the use of the 3923 spark plugs. He determined that many TPS units and throttle body idle settings weren't optimal. The TPS issue became his Zero=Zero article. He wrote about his testing and the results and posted them to the IBMWR long before BMW MOA even had a web site. I had the pleasure of working beside Rob on a few occasions at rallies when folks had "incurable" surging that Rob could make disappear. Long before the invention of the Techlusion devices or the Booster Plug Rob was the guru regarding Oilhead fuel mixture control.

    Today we hear about yanking Cat Code plugs, or resetting throttle bodies, or Zero=Zero, or using Autolite 3923 spark plugs, and many people don't know where or how those techniques came about. I would recommend that anybody who has an R1100 that surges go to the Oilhead Tech section of the IBMWR.org web site and look for anything written by Rob. It will be an eye opener. If you happen to be able to find the October and November 2008 issues of the Owners News you might like my two-part series titled Internal Combustion.
    Thanks for adding this history, particularly Rob's background (which I appreciate since my 30 year business career was in the development of electronic test equipment, including automotive electronics). Many of us have read and reread these terrific articles and the results of Rob's meticulous analysis. If there is anything missing, it seems that Rob didn't have access to O2 and AFR dataloggers, (which tell a very interesting story at least on the 1150), and make's Rob's insights all the more impressive.

    It looks to me like the no-cat-code plug map isn't a limp home map but rather, it was intended to be the map for non-catalytic converter motorcyles delivered where cats weren't required by law. That being the case, I believe that if an AFR logger was fitted to an R1100, we would find that it doesn't exhibit the limp-home fueling variation that I've measured on the R1150. The R1150 without CAT exhibits a definite limp-home flavor that is a mixture centered on 14.7 but varying ??10%, a range more than twice the width of the Closed Loop mixture spread.

    I think the AFR and spark details of the R1150 are now pretty well known. It would be interesting to see the same logs from an R1100, especially the no-cat map. We'll have to wait until someone fits an LC-1 or something like it. These 10 and 20 year old motorcyles still have some secrets to tell.

    In the meantime I'd like to find your 2008 On ariticles, thanks for pointing them out.
    Last edited by Roger 04 RT; 11-12-2012 at 04:26 PM.

  10. #10
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    In addition to being an outstanding investigative technician, Rob was one of the finest people you could ever hope to meet.
    Thanks for the long-term perspective, Paul.
    Ride Safe, Ride Lots

  11. #11
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    I had the Bosch duals. Pulled them out and replaced with Autolites. Runs much better with Autolites. Cheaper is another plus. I recently put in double platinum Autolites, which worked even better. The 3923's get tired near the end. The Platinum plugs will make them remain fresh longer. You can find them at Walmarts if your dealer isn't willing to help. Try them and see if they help you.

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