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Old 02-06-2011, 10:04 AM   #1
Rapid Dog OP
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Question The trouble(s) with this '81 R100 Airhead

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?

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.

Generator stays on light 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?

Any insight from those in the know is appreciado..
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Rapid Dog screwed with this post 02-07-2011 at 09:27 AM
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Old 02-06-2011, 10:23 AM   #2
fishkens
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Weird buzz in '81 R100 on start.
Starter relay? Sure sounds like it. Remove the tank and put your finger on the relay when trying to start. If the buzzing is coming from the relay it's probably on its last leg. You can take it apart and clean it but it's best to replace it.

Rebuilt carbs won't adjust.
Idle screw? If turning it doesn't affect the idle speed then the circuit seems to be clogged. Try blowing it out.

Generator light on dimly.
Dim alt lamp? I had that condition for years. Tried cleaning contacts, etc. It finally went away when I replaced the diode board with Rick's. Not certain if it was the board or contacts but that fixed it.

Neutral light inconsistent. Do these switches act up or just die?
Yep. My guess is that you'll be pulling in the clutch lever more and more until it's 100% of the time and the neutral light never lights. Bad neutral switch at the tranny. They go bad regularly.
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Old 02-06-2011, 10:24 AM   #3
Country Doc
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I had almost that exact same carb issue on my slash 5. Turned out that there was a tiny, tiny, tiny little passageway JUST behind the butterfly that sprays fuel for idle and just off idle, up to about 2k rpm where the main part of the needle takes over most of the fuel delivery.

I forget the name of this passage. I could not even see it on my carb, as it was just gummed up flush to the surface of the carb throat, and was invisible. I needed a magnifying glass, tiny sharp needle, and I had to compare side by side with the other carb to figure out where the hole was supposed to be.

Ok, correction , all this troubleshooting to find the passage was actually done by bmwrench, after I tried to sync my carbs and adjust them a thousand times and couldn't get the thing running right.

maybe worth a look.

dc
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Old 02-06-2011, 10:32 AM   #4
supershaft
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Take the tank of and see which one it is. It can't get much simpler than that.

Did you make sure the two small holes in the carb for the idle circuit are positively clear? It takes compressed air IMO. IF your carbs are good , you have got leaking valves. Listen with a leak down tester. They will not idle right with leaking valves.

Test the diodes. Make sure nothing is grounding on the hot side of the diode board. Make sure none of the other wires are shorting out somewhere they are rubbing on something. Just LOOKING is a good test for this. Make sure your brushes are making good contact. Find a good rotor to try. In this situation, testing it might not show the problem.

When the light is acting up, test the switch at the leads. If it tests good you have got to trace the wires. It's probably the switch.

Good luck!
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Old 02-06-2011, 11:32 AM   #5
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Take the tank of and see which one it is.
Trouble is, the buzzing is new, definitely under the tank, but doesn't happen all the time.
Charged the battery overnight.
Just went out there and removed the tank. Hit the starter several times, no buzz...weird. I have a feeling it's got to do with lack of juice from the battery.

It takes compressed air IMO.
Yes, shot a good blast straight up he idle screw hole, gas sprayed everywhere..

test the switch at the leads

I'll give that a try for sure.
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'81 R100RS Rattlecandy Red/'06 950 ADV Orangeboom/91 R100GSPD Derelict

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Old 02-06-2011, 11:41 AM   #6
supershaft
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That in no way guarantees that those wholes are open. You have to block the mixture screw and the idle intake at the back of the carb at the same time and then squirt air up the pilot jet boss look and see it BOTH holes are working.

Good luck!
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Old 02-06-2011, 11:54 AM   #7
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Quote:
Originally Posted by supershaft View Post
That in no way guarantees that those wholes are open. You have to block the mixture screw and the idle intake at the back of the carb at the same time and then squirt air up the pilot jet boss look and see it BOTH holes are working.

Good luck!

Another way to tackle this is to use carb (or brake cleaner), insert the plastic extension tube into the various carb body passages and spray.. then block the hole the spray exits with your finger and spray again, and then reverse direction.


IIRC, the idle passage exits in two places, in the throat of the carb as well into the body.. you need to pull our the needle jet and mains for that one.

But, as said above, if the idle screw doesn't do anything, you do have a blocked passage. No if, ands or buts about that.
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Old 02-06-2011, 12:33 PM   #8
supershaft
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Quote:
Originally Posted by SOLO LOBO View Post
Another way to tackle this is to use carb (or brake cleaner), insert the plastic extension tube into the various carb body passages and spray.. then block the hole the spray exits with your finger and spray again, and then reverse direction.


IIRC, the idle passage exits in two places, in the throat of the carb as well into the body.. you need to pull our the needle jet and mains for that one.

But, as said above, if the idle screw doesn't do anything, you do have a blocked passage. No if, ands or buts about that.
Actually the idle circuit is completely separate from the passage way that goes to the atomizer on top of the main jet stack. The other whole in the back of the carb is for the idle circuit.
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