The trouble(s) with this '81 R100 Airhead

[Rapid Dog]

1981 R100RS recently gone thru, fresh heads, coils, wires, plugs, dual plugged.

Weird buzz in '81 R100 on start.
I've been fiddling with the carbs, starting the motor alot.
I've had the starter rebuilt as a note. Also a new ICU under the tank.

I noticed a few times (and this is a new one) that when I push the start button I hear a buzzing sound under the tank, like a relay or something, just before it wants to actual turn the starter motor. This is intermittent.

What's that? Is it a starter relay going south?

Generator light on dimly.
This is minor but the gen light never seems to go completely off even at highway speeds. I've cleaned all the contacts, battery is charging.

Haven't figured this one out at all.
As a note, the voltmeter goes whack and pins of and on on the + side, I have a fresh one coming this week, we'll see how that pans out...

Neutral light inconsistent.
Half the time I have to pull in the clutch to start as the neutral light does come on., sometimes it does. Totally intermittent.
I cleaned the clutch switch at the lever, it works fine. Cleaned contacts at both ends of the neutral switch wire.

Do these switches act up or just die?

Rebuilt carbs won't adjust.
Soaked the carbs in Pinesol for 48 hours (disassembled).
Blew out all the passages with compressed air and reassembled with al new o-rings and float needles (shot).
The right side is still sputtering and backfiring at idle.
Anything below 2500 RPM and it surges and sputters.
WFO it seems to run good but of course, backfires when you shut the throttle.
I even ran it around the local loop with the synch port rubbers of by mistake, didn't seem to make much diff in the way it ran. Weird.

While synching I see that the right side idle screw doesn't seem to have any effect on the Twinmax readout when adjusting it. Checked cables for free play etc, cables are new. Diaphrams are good.

Worn out idle screw? I'm going to order up a new one for both sides Monday.

Any insight from those in the know is appreciado...

[Rob Frankham]

1981 R100RS recently gone thru, fresh heads, coils, wires, plugs, dual plugged.

Weird buzz in '81 R100 on start.
I've been fiddling with the carbs, starting the motor alot.
I've had the starter rebuilt as a note. Also a new ICU under the tank.

I noticed a few times (and this is a new one) that when I push the start button I hear a buzzing sound under the tank, like a relay or something, just before it wants to actual turn the starter motor. This is intermittent.

What's that? Is it a starter relay going south?

Could be the starter relay... in fact it probably is the starter relay that's buzzing... the cause could well be dirty connections to the relay. It could also be dirty connections virtually anywhere in the path from the battery, via the starter relay to the ignition switch then via the starter button back to the starter relay. This also incudes all connections in the Favourite is the relay connections in the eath line. Favourite, though, is the starter relay connections.

Generator light on dimly.
This is minor but the gen light never seems to go completely off even at highway speeds. I've cleaned all the contacts, battery is charging.

Most of the time this is due to a defective diode on the diode board (although sometimes a bad earth can have similar symptoms). If it is a diode, even though the bike appears to be charging normaly, the charge circuit will only have a fraction of the max output.

Haven't figured this one out at all.
As a note, the voltmeter goes whack and pins of and on on the + side, I have a fresh one coming this week, we'll see how that pans out...

Oh dear, I doubt this is the voltmeter... they don't usually over read. This normally means a regulator problem. The only way to be sure is to check the output using an accurate multimeter.

Neutral light inconsistent.
Half the time I have to pull in the clutch to start as the neutral light does come on., sometimes it does. Totally intermittent.
I cleaned the clutch switch at the lever, it works fine. Cleaned contacts at both ends of the neutral switch wire.

Do these switches act up or just die?

It sounds to me as though the clutch switch is working perfectly, it's the neutral switch that needs attention. Unfortunately, this isn't easy to get at as its on the bottom of the transmission between it and the sump extension. Check the connections to the switch and the ground, which is attached to the lower left transmission engine bolt. Failing this, you may want to just live with it until you next have the transmission out. It is possible without but a real PITA.

Rebuilt carbs won't adjust.
Soaked the carbs in Pinesol for 48 hours (disassembled).
Blew out all the passages with compressed air and reassembled with al new o-rings and float needles (shot).
The right side is still sputtering and backfiring at idle.
Anything below 2500 RPM and it surges and sputters.
WFO it seems to run good but of course, backfires when you shut the throttle.
I even ran it around the local loop with the synch port rubbers of by mistake, didn't seem to make much diff in the way it ran. Weird.

While synching I see that the right side idle screw doesn't seem to have any effect on the Twinmax readout when adjusting it. Checked cables for free play etc, cables are new. Diaphrams are good.

Worn out idle screw? I'm going to order up a new one for both sides Monday.

Any insight from those in the know is appreciado...

I doubt this is the idle screws... it sounds as though there is still a gallery in the carb blocked. Have you checked the gallery and tiny jet in the corner of the float bowl? Failing that, have you made sure that there is no air getting in to the system at the rubber carb to head connectors and that the choke assemblies are tightly fixed.


Good luck

Rob

P.S. just reading thorugh and I realise that all of the electrical symptoms could be explained by a bad earth connection... no promises but I think that's where I'd start.

Rob

[Ken in Oklahoma]

Rapid Dog, you've given us some good information, but I would want more. How about some of the recent history of this bike. Is the bike new to you? Are you trying to resurrect a non running bike after doing a lot of work on it? Or are these problems that have been showing up one by one and you're wanting to get rid of them? What do you mean by "gone through". And has the bike ever run correctly in the current configuration. I think you get the idea. Most trouble shooters like a lot of information. They are capable of setting aside information that doesn't seem pertinent.

And while your giving us information, how about telling us about your airhead experience and mechanical skills. That will help us tailor our ideas to your abilities.



Weird buzz in '81 R100 on start.
What does the buzz sound like? Is it a fairly light, fairly high pitched buzz, or more like a louder clatter? As for the starter relay, my experience has been that they work until they don't. No buzzing ever. What I'm suspicious of is either a marginal battery or marginal battery connections. The clattering would be coming from the starter solenoid, under the engine top cover. What happens is that there is enough battery power to engage the solenoid. The solenoid is a high current switch to the starter windings. So the solenoid will engage the starter. But because the battery is bad or because the battery cables or connections aren't sufficient the voltage drops so low that the solenoid can't maintain the engagement. Then the voltage will rise again and the solenoid will try to engage the starter again, until the voltage drops again. The result is a distinctive, fairly loud clatter, as opposed to a light fast sounding buzz.



Rebuilt carbs won't adjust.

I have a low expectation for fixing carbs by soaking them in whatever solution. You say you blew out the passages I'm wondering. Did you blow out all the passages, including the very small ones in front of and behind the throttle butterfly? I'm never satisfied that I've cleared the passages until a get a huge volume of carb cleaner through the large ones and have used a thin wire to make sure the very small passages have indeed been cleaned. There are diagrams of the carbs in some of the repair manuals and I thing some available on the Bing agency web site. Unfortunately, to know for sure that your carb passageways are really clean you'll need to understand where all the carb passageways are and it's nice if you know what the carb passageways do. You can learn a lot by looking at the cast protrusions on the carb bodies and the plugs here and there.

The carbs are going to have to be without issues before you're going to have much luck syncing them. I wouldn't worry about that until you're confident that your carbs are functioning properly.


Generator light on dimly.
How do you know the battery is charging or charging as much as it should? Your bike's voltmeter, even if it were working, would be next to useless for this. The problem is that there is a voltage drop between the voltmeter and the battery. You really need to measure the voltage at the battery when you're trying to sort out charging problems. A fully charged battery with no load on it should read about 12.6 to 12.7 volts. When the battery is being charged properly and is nearly charged you should be seeing something over 14 volts at the battery.

As an aside, sometimes the diode board will have one of the large diodes go bad. The battery will charge a little if there's no significant load on it, but won't be able to maintain a higher current draw like the headlight.



Good luck, and you'll be getting some more ideas soon.

Editing: I see Rob Frankham posted while I was composing mine. That's a good thing.



Ken

[Rapid Dog]

Well if you want to know the history, there is lots to read so pull up a chair...
Here's the story from the P.O., a fella you may know: http://www.bmwmoa.org/forum/showthread. ... ht=Telefix

Here's what I've done: http://www.rapiddog.net/RSBUILD/BUILD.htm

Last night I pulled the alternator, rotor, and diode board since I haven't been there yet.
Rotor measures resistance at 3.9ohms, from what I've read 3.4-3.74 means it's 'dood'.
The PO mentioned he'd replaced all the bulbs in the bike. Is it possible the gen light is dim due to it being mismatched with the (wjhat seems to be) higher output rotor?
I'm grabbibg at straws here. I am very elctrical challanged.

how do I rtest the diode board and the alternator itself?

[Ken in Oklahoma]

how do I rtest the diode board and the alternator itself?

Rob Frankham has an excellent write up on testing the diode board. It's the one I use. Here's the link: http://robfrankham.co.uk/bike/testing_t ... _board.htm



Ken

[Rapid Dog]

Thanks for that, followed robf's test procedure, diode board checks out.
Rotor checks out at 3.8+ ohms.
Alternator case checks out all circuits at .6ohms.
So I guess all the charging stuff is O.K. I guess I'm going to have to pull the top cover and check the wires up top...