I recently acquired an '88 r100rt which hasn't moved in 10+ years. I posted about it about a year ago, but I didn't do much with it, as it was in New Jersey and I was up at school in New York. I've since moved it up to New York with me so I can work on it this summer. I'm studying Aerospace Engineering, but the most valuable thing I've learned is to look for help when you don't know what you're doing. So, I'm here. I currently just want to get the bike to turn over so I know that I'm not putting lots of money into something that will never run.
The Good:
-When placed in high gear, and the spark plugs removed, the back wheel can spin, which means there isn't significant ring/piston/cylinder damage (it sat with the spark plugs out for some time).
-After disassembling the carbs they looked to be in very good condition. They'll probably need another rebuild before the bike runs for real.
-I've replaced the oil for the engine, trans, shaft, and bevel. After it runs a little bit I'll do this again.
-I've cleaned the tank with diesel and then vinegar to remove most of the rust, and have replaced the petcock straws and in-tank filter, as well as the fuel hoses
The Bad:
-I replaced the battery and turned the ignition switch and... nothing happened... I don't know what to check. I've worked on dirtbikes but they didn't have much as far as an electrical system, so I'm fairly new at this aspect. I believe this is my biggest problem right now. With the ignition disconnected from the bike and in the "on" position, there was continuity between 3 of the 4 leads and the ground, but I'm not sure if that is indicative of a "good" ignition switch. (I'll figure out which ones have continuity and update the post tomorrow. I've disconnected all the lights other than those in gauge lights. Both fuses below the seat look to be in good condition. I could check the clutch switch, though I'm not sure how to test it without tearing it apart, and I don't know if its meant to be 'normally open' or 'normally closed'.
Oh and before you say anything about the lack of fairings - they are all for sale in the "for sale- parts" section of the website. I hope they go to a good home.
Welcome Aboard !
Here's a thread that should help with the most common issues....
https://www.airheads.org/forum/technical-discussions/992-new-owner-primer-tips-to-get-your-airhead-back-on-the-road
Owning an old Airhead is easy.
Keeping an old Airhead running great is the true test.
Thank you, I'll start here!
Some thoughts about your electrical issue...
► The BMW is fairly strange in that there is no "main" fuse" that is common on other brands. I tell you this for 2 reasons. 1. Often times owners see that there is no fuse, see danger, and add one. They can install this anywhere in the RED wire between the battery and ignition switch. The quality of the installation of said "main fuse" can vary from military grade solder and heat shrink, all the way to home lamp repair complete with wire nuts. So the quality of the installation can be the fault itself.
2. On an unaltered stock harness, the absence of a main fuse means that you must be very careful where and how you test. If you make a mistake you run the risk of smoking a significant portion of the $300 harness. Don't ask me how I know this. Beware of any RED wire as a potential villain (including the RED wire to the clock), because it runs directly to the battery.
► Per normal design, the power to the ignition switch is not the same path as the power to the starter motor. Once you are sure the harness is sending power to the starter button, then you must explore the path of high current to the starter motor itself. One of the quirks of the German cabling is that both the heavy Positive and Negative starter cables have their faults. This detail is covered in the referenced article.
► You are right to check out the ignition switch, they do fail with regularity. Power enters on the RED wire, and leaves on solid Green and solid Gray.
► Green and Gray are also seen at the fuse box. I highly suggest you remove the old-style German fuse box (complete) and plug modern American 10A ATM "flat pack" fuses directly into the harness. This will add a great deal more reliability to the system. (I don't think it's you fault,this is a move for the future.)
Hope this helps.
Owning an old Airhead is easy.
Keeping an old Airhead running great is the true test.
-Can I safely jump the ignition switch to see if that is my issue?
-Is there a way I can supply power directly to the starter motor to check compression?
-How do I test if power is being sent to the ignition switch? Forgive my lack of electrical terminology, but are the rest of the electronics "before" or "after" the ignition switch, meaning does current flow from the positive side of the battery to the switch and then to all of the other components before returning to the ground or v/v?
Testing of the leads from the ignition switch showed continuity between the ground and the red wire, the green wire, and the double red wires that splice to one connection at the ignition switch, as well as the positive lead to the gray wire. These are pictured below:
On the actual switch, all pins have continuity with each other except the topmost pin in the image below. Could this be the source of my problems? This pin also feels a little bit loose, whereas the others feel more solid. The pin two to the right of it was not connected to anything during disassembly and is discolored from exposure. Not sure if this is normal.
I also found that this plug for the green and brown wires was not connected. I don't remember unplugging it:
► Forget continuity testing. The way you are using it doesn't tell you anything.
► Instead use a "mechanic's test lamp", which looks like an ice pick with a long wire. Clip the wire to a solid "ground" like the negative post of the battery, or an aluminum engine fin. Use this to search for the presence of electrical power. When you find it, a light bulb in the handle of the "ice pick" will illuminate.
• First place to touch is the Positive battery post. Lamp should light. (Is the battery even "hot"?)
• Next place is the RED wire at the battery terminal. (Is 12V getting into the RED wire?)
• Next place is the RED wire at the ignition switch. (Is 12V getting thru the RED wire?)
• Next place is the various terminals on the rear of the ignition switch in ALL the switch position. (Is 12V getting thru the switch?)
• And so on... A to B, B to C, C to D, etc in an extremely logical order.
► Guided by the schematic, proceed in a logical order from the Ign Sw to the Starter Relay, thru the relay, to the Starter Solenoid.
► Then you can use the same logic on the Pos and Neg high current leads going to the engine and the Starter Motor.
► Question:
Is there a way I can supply power directly to the starter motor to check compression?
Yes. The battery positive terminal (which is powered all the time) is sitting about 3/8" away from the low current Starter Solenoid terminal which is waiting on 12V from the Starter Relay. I'll let the budding engineer figure out how to bridge that gap; every first year car thief already knows.
► Speaking of compression, it's best practice to remove the 2 carbs from the cyl heads when performing that test.
Hope this helps.
Owning an old Airhead is easy.
Keeping an old Airhead running great is the true test.
Ok, I feel kind of stupid now. I didn't realize that there were TWO leads that connect the positive terminal on the battery. My friend was in the shop with me and we were talking about it and I was showing him what I had already tested and I noticed this:
Turns out the connector completely broke off. I connected it to the terminal, turned the key, and everything worked fine. I compression tested it and both cylinders were just under 150 psi. I have spark on both sides. Just have to clean the rust out of the tank and rebuild the carbs and I should be good to go. Thanks for all the help!
Ok, I feel kind of stupid now. I didn't realize that there were TWO leads that connect the positive terminal on the battery. My friend was in the shop with me and we were talking about it and I was showing him what I had already tested and I noticed this:
Turns out the connector completely broke off. I connected it to the terminal, turned the key, and everything worked fine. I compression tested it and both cylinders were just under 150. I have spark on both sides. Just have to clean the rust out of the tank and rebuild the carbs and I should be good to go. Thanks for all the help!
Ok, I feel kind of stupid now.
No sir, you were ignorant. Now, education has replaced your ignorance. Unlike ignorance, stupidity cannot be fixed. 🙂
I didn't realize that there were TWO leads that connect the positive terminal on the battery. My friend was in the shop with me and we were talking about it and I was showing him what I had already tested and I noticed this:
That looks to be the 12ga wire that supplies power into the harness. Rather than merely replacing the missing ring lug, I highly suggest that you take the time to insert a flat pack fuse holder on the end of the wire. That will offer the missing fuse protection for the harness.
You can get hooded, weather-proof fuse holders LIKE THIS with 16 and 12ga wires at your LAPS. Buy one with heavy gauge wire and stick a 20A fuse in there.
• The gray wire at the ignition switch also needs the female terminal added back to the harness. Do a really jam up job on that, because gray supplies power to all the bike's lighting.
Hope this helps.
Owning an old Airhead is easy.
Keeping an old Airhead running great is the true test.
Thanks for the tip on an inline fuse- didn't think about that.
I planned on making that grey wire a little less ghetto but I just wanted to make sure everything worked
Any tips on jetting/tuning if I switch to pod filters?
Any tips on jetting/tuning if I switch to pod filters?
Please explain why in heavens you's want to consider this. It can't be for performance, because the low compression RT with that large fairing simply doesn't have any.
Besides, I think the inlet tube helps physically support the carb at the intake side. You'd also be swapping a large air cavity for an extremely small one. That can't be good; especially in the wet. And then what would you do with the engine breather ?
The hot setup on those models is to get an air intake/air filter cover with 2 large snouts. Lots of those came with one or more small snouts to reduce intake noise.
Owning an old Airhead is easy.
Keeping an old Airhead running great is the true test.
I wanted to because I think it looks better, and I was planning on moving my battery to where the airbox was. If it is that hard to make it run well then maybe I'll reconsider. I can always move the battery to under the transmission.
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