So my "new to me" 93 R100gs and I have been having some growing pains over the past month or so... I bought her w/ 8300 miles on the ODO and now it reads 8450, but they have all been tuning miles. The bike had 2 POs, and the last owner probably had her sitting for several years with little exercise and humid DEEP-South gas in the tank (MAN it was nasty). So my initial attempts of getting her running revolved around the assumption that the tank was full of rusty, varnishy, bad, molassessey gas. I was partly right. A few Phosphoric Acid and Evapo-Rust (http://www.evapo-rust.com/ - NOT the other site that the Goog returns) treatments later, and I think I have a good enough tune to warm up for a final tune and go riding! EXCEPT there is a bit of a surging miss at constant throttle, no matter what speed or gear. Just as if a cylinder isn't firing but in never lasts more than once in a row, but fairly regularly for a given throttle input. Break down and clean the carbs yet again, to the point now where there is very little, if any, nasty gas residue coming through the carbs prior to cleaning. Well, if it isn't gas, it's got to be air or spark right? I have the airbox-to-carb-to-head tubes perfectly sealed now after several days of finagling. I am confident in my PAS plugging effort (both at the heads and various Vac. tubes, etc.). New test ride works great for 20 miles, except the "miss" is still there. Triple-checked the plug gap (.07mm), and the valves are proper (.15mm intake, .20 exh). I am getting spark at both plugs (new wires, and tested plugs out against the heads). Carbs are perfect now (I am a 64 series breakdown expert right about now). Attempts to fine tune the balance have one side running perfect, the other bogs with any input from the mixture screw. Seems like the left is perfect, the right stupid. Next day (with no changes!) the right cylinder is heating up with firing attempts and the left is stone cold. Swap the plug wires, same result - right hot, left cold. Both cylinders are moving, but both aren't firing. So WTF?!? I refer to my trusty BMW Motorrad GmbH+Co. Repair Manual for coil and ignition Multimeter testing... I might have the culprit. And here is where you, trusty reader, for having read this far, get to add your valuable input! The repair manual says test Primary Resistance between terminals 15 and 1 (should be 1.10-1.32 Ohm) and between 4a and 4b (should be 7.5-9.15 Ohm). I should mention this bike has the "improved" modern coil w/ the black body, spade connectors for power, and orange plug wire terminals, not the old gray coil w/ screw on power terminals. So I test the terminals that hold the GRN/BLK wires (power), and find 0, that's ZERO Ohms between them. Test the plug wire terminals between each other and receive a value each time within limit of the 7.5-9.15 Ohms. Since the repair manual is delightfully vague on exactly which terminal is which (and I couldn't read any numbers near any of them), I am guessing that the GRN/BLK spade terminals are my "15 and 1" terminals referred to in the manual. Is this a correct assumption? In which case, I have ZERO Ohms between them where I should have 1.10-1.32 Ohms. So coil is bad right? I just want to make sure before I drop the large money on a replacement of any kind. Should I go with genuine BMW taxed part or Thunderchild or MotoElekt Dyna, or "???"? Thanks for reading and your input!
If it has the grey coil, which i think it does then there is a good chance it is bad, they are known for going bad, usually they have fine hair line cracks in them. You can get a Harley coil for 1/2 half or less than the BMW coil and easily make a bracket, the HD coil is the one from the EVO era motors 85-98, not sure of the part number but if you search old school you can find the number, may try airhead tips and tricks, i am sure the full details are there. Somebody please correct me if i am wrong on this info, going from my memory and it gets worse every day.
I was about to state that coils do not fail, OK .001% of the time, but if Chrome says there is a known problem with these..... So I will ask, when you say you cleaned the carbs, did you pull out the pilot jets, and fuel screws, and blow through them, to verify the are clear?
3 times, yes. I know it sounds a bit like a gas/air issue, but I can attest that the carbs are good. I have all new jets/needles/diaphragms/gaskets/o-rings/etc. in the carbs. I even unscrewed and cleaned the bowl jet for the choke system. I too, expect the electric components to be the last to fail, that's why I'm at my wits end since I've triple checked all physical (air/gas) systems multiple times.
I would guess that coils do go bad, like anything thats got to hold those crazy electrons innit. Its not often though, except for those grey ones. Despite your problems, I dont think there's significant difference in reliability over the major brands, anymore, because if there is a BASIC item, its a freekin coil of wire around a magnet. I still have a later BMW coil. Plug wires are all cracked... time to replace them again right after the spray silicon wears off again.
Are you sure that's not supposed to be kOhm ( Kilo Ohm) ? Also : how accurate is your multimeter > 1 ohm is next to f....all : its probably better to measure if its not shorting. Coils, in my experience, are a lot harder to test then made to believe by the manual. Plenty of coils check out on the bench, but show a problem when on the vehicle. Mostly when a coil is faulty it shows up as a misfire during hard acceleration, because that's when the voltage requirement is at it's highest ( high cylinder pressures). Off course when the insulation is faulty, all bets are off. Best to check with a new, or known coil. Just my 02 cents.
Well the manual did specify the range with just the Ohm sign, but I did test on the VOhm plug in my Multimeter, on the 20k setting which is the lowest range for V Ohms on my meter. I zeroed the meter several times during the process to ensure I wasn't seeing something funny (zero by touching the leads together). And I do happen to have an 83 RT here so I tested the twin coils in the same manner. The plug wire terminals on this one gave me a resistance above the range as I was expecting on the GS, so that's what makes me think the GS coils are bad, since I got 0.00 reading - the same as the zero reading procedure. And this Multimeter is just a $30 job from a local hardware store, but from what I've read, any reasonably priced Digital Multimeter is accurate enough for the types of tests we need on our bikes (I won't buy a $200 meter if a $30 will suffice, but I also won't trust a $15 one). If not the coils, my next suspect is the ICU. I think the POs might have done some shade tree tuning by removing the plug wires (!!!) so I can't rule that out. How would I test this w/ the meter if only to rule it out? The BMW repair manual is again delightfully vague here, with no pictures, only terminal #s as decriptions...
I should also add that in the times where I've had it closely balanced enough to take warm-up test rides, it accelerated strong, seemingly without the "misses.". It seems to do the missing at constant throttle position (at least that's when it is most evident). And the tuning/balance seemed to get worse and harder to fine tune once fully warmed - this is what led me to suspect electrics...
I'll admit that coils and condensers do not fail very often, but anything that is made will break at some time. I had a similar issue on a Morris Minor everything would work real peachy for about 10 minutes then the missing started. Turned out the coil would 'over-heat' and start failing to fire.
It could be just about anything. The only real way to test a coil is to replace it and see if that fixes the issue. I have found spark plug caps causing something like you describe as well as sucked in enricher body gaskets. Did you put new gaskets in EVERY time you had the carbs apart? You should! Could luck! You could write a book on what could be causing the symptoms you describe.
switch the coils around and see if that cylinder fires- I had one of the black coils fail coming cross country. It's usually the last suspect but it does happen.
That's been done, mentioned in my first post. Although just the plug wires were swapped since this is a single body dual output coil. SUPERSHAFT- this has happened with both old and new plug wires, brand new plugs properly gapped, etc. Also, I replaced the enrichener gaskets at the first rebuild (the major one), the others have just been cleanings. I did remove the enricheners this last time just to verify evrything, but prior to that the E. gaskets had been undisturbed as a new item. I am terribly puzzled by the left cyl. not firing no matter where the plugs wires are... I'll be checking my valves again tonight to make sure I don't have a physical and electrical issue simultaneously.
You can always swap your carbs around and see if the problem changes then from one cylinder to the other. BTW the engine reacts very strongly on the mixture screws on my GS : 1/8 of a turn makes a difference when idling. Another thing could be the sealing of the diaphragm covers. Put some thick grease, or even RTV on the joint. My guess is that your coil is OK, but that you have a carburettor problem. Also check for sealing of the carb/ head joint. When it is idling you can spray some CRC , or even brake cleaner around that area, and see if the motor reacts to that. You've got a nice bike , stay at it. You could also do a leak down test , just to top it all off. I'm going to shut up now. Enough people already adding to the confusion....
BOETJE - good call on switching the carbs, I'd have never thought of that. I was talking with Rusty at MaxBMW yesterday and he mentioned the exact same thing. Pretty smart trick, but I probably won't have to worry with it. I discovered why the left side wasn't firing at all, and sadly it was all user error. During my last warm up ride, I stopped at a store and noticed a puddle of gas underneath the left carb. Since I'd been in and out of the carbs so many times, I assumed a pinched the bowl gasket or the floats were set a bit high. Without measuring, I bent the float back down when I got home and straightened the bowl gasket. Turns out I bent the float tab too far and there was barely any gas in the bowl. The leak was actually a cracked plastic T-fitting in the gas line, which will soon be replaced with the metal ones from the /6&/7 era. I now have both floats set to 24mm gas in the bowl per Snowbum's directions. Supershaft, BOETJE - re carb leaks: Yeah I'd previously done the carb cleaner spray around all joints and carb tops, even on the enricheners. No runaway idle when doing that so I'm fairly confident that the gas/air passages and carbs are sealed. I do like the idea of silicone grease on the diaphrams and enrichener gaskets when assembling, which I did when they were last assembled. The grease does help keep the slide centered via the tab on the diaphragm, and my thought was also that it would help seal possible leaks. UPDATE TO THE COIL: Spoke to Rick at MotoElekt yesterday, described the whole sordid affair, and he said "yes it sounds like your coil might be bad, but I've honestly only heard of ONE (of the "improved" BMW coils) that has failed in the wild." Then I told him the bit of info that I withheld here so as not to taint the conclusion gathering process: The PO had another individual sell the bike for him, and this guy had a Harley race bike mechanic who helped to get it running after sitting for so long. He mentioned that the mechanic pulled the plug wires to do the carb balancing, etc. I immediately told him that this was B A D, bad for BMW elect. ignitions and hopefully it didn't fry the coil or ICU. This is another reason why I suspect the coil, and as soon as I told Rick this he said, "well yeah, probably the coil." Thankfully he thought the ICU would probably be ok, but the coil since it is the last item in the chain before the wires and plugs, probably bore the brunt of the non-grounded plug. So I have a BLUE 0.7 Ohm coil on the way. Hopefully see that Tuesday. I performed some other MM tests, and figured out which terminals were which on the coil, per the attached pict. I tested the hot and ground wires to the coil with the ignition on, and per Clymers, there should be close to battery voltage here when plugged into the coil w/ ignition on (and plug wires in and on plugs). With the wires unplugged, my MM read 12.3 V on these wires (battery V was 12.4). Plugged into the coil there were ZERO volts between terms. 15 to 1. Testing each terminal from the coil to a separate ground (15 and ground w/ the MM, then 1 and ground), gave 11.5-12.0 volts, which is a bit low. So I'm pretty sure something is up with the coil after all - no voltage reading for 15 and 1 when the circuit is hot and plugged to the harness, no resistance reading for 15 and 1 when unplugged from the harness, and 12.6 KOhms resistance across 4A and 4B (way too high). Tested the ICU per Clymers and BMW Repair Manual (Clymers has a diagram of which wires are what number!). I got 12.3 V between terms. 2 and 4 (good reading), and got 11.x V between terms. 3 and 5 (also good). So hopefully my ICU is still kicking. I didn't do a reading on the pulled 5 wire because I didn't want to break into the harness and the prior two tests were good. I'll let everyone know the verdict when I get the new coil Tues/Wed. If all goes well I'll be taking my maiden voyage to the Ozarks on the GS next weekend. *fingers crossed*
Received MaxBMW parts and MotoElekt Dyna blue coil today... Storms and tornado warnings prevented a full eval and tune - BUT! - Results initially encouraging. Full report (and picts!) at 11... (er, tomorrow night)
I have had plugs that show a big fat spark against the head but under compression they wouldn't fire, just for kick I'd consider a new pair.
