81 RS weak start/ battery problem

[9842]

Hey Guys
Got a 81 RS, have owned it since 91 and love the bike but have allways had a starting problem. If I ride it often it will allways start. I keep it on a battery tender and after a week or so it just won't turn over. In the 17 years I have had it I have put 4 or 5 batteries in it. Problem is alwas the same if the battery is new or old. Tender is suppose to keep the battery charged up but seems like it does not do the trick. Any Ideas on how to fix this problem would be great.
Thanks Brian
9842

[jpberens43639]

I've had an 81 R100RS for a long long time.

I've tried different batteries, got 6 years out of a cheap peice O junk once, and only 2 years from a BMW battery.

Now use an " Odyssey " battery. #PC680 i think.

Thing is kind of narrow, but MAN!!! I can ignor it for a couple months with NO charger on it and it starts right up! 2 years old now.

Check your system too with a multi meter and make sure there is minimal to no draw on it when teh ignition is off. Only thing that should be pulling juice is the clock.

[rpeckham136133]

And make sure that connections are tight and clean..... both positive and negative.

Pay particular attention to both ends of the heavy cables, positive AND negative. DC current needs a loop to work! Heavy positive goes to starter from battery. Heavy negative goes from engine/tranny bolt to battery.

[nealart]

Is it always the same tender that you are using?

[20774]

My Dad's original '81 RT (long since gone) used to only show a little over 13 volts on the dash voltmeter. Now that's usually a little low based upon where it is in the circuit, but might be a little too low. Best thing to do is find out what kind of voltage you have across the battery from the bike's charging system. After a ride with the bike somewhat warm, come back to the house and put a voltmeter across the battery terminals directly. Restart the bike and rev the engine to about 3K RPM. You should be getting fairly close to 14v. If not, then your tender is having to work overtime to put back in what the bike system can't do.

Your starter might be dragging and not spinning as fast as it should...might need some attention.

If the cables are original and have built up some corrosion, the starter might not be getting all the current it needs to start. A cable might look fine, but often they will corrode underneath the sheathing where it's not visible. You might want to ohm each of the main cables and make sure there's no excess resistance. Corrosion will increase the resistance.

A battery every 4 years is not bad...might be good by some standards. But maybe your starter is not getting everything it needs...

[9842]

Hi
I use a tender and a tender jounior. I also have a 75/5 that I charge once in a while. I switch chargers not thinking about it. I also have a powerful 12 volt charger, I am going to give it a charge with this one. I have been told that tenders only keep voltage at one level and do not charge up, so if the battery is run down the tender will hold the run down charge but will not raise the volts.
BRIAN

[20774]

I have been told that tenders only keep voltage at one level and do not charge up, so if the battery is run down the tender will hold the run down charge but will not raise the volts.

I think it depends on the charger...best to read the instructions or surf the internet. They do make smart chargers which are designed to get the battery back up to proper voltage and then back off on the charge volt/current to maintain the best voltage level...called "float" charge I believe. I bought a cheapo float charger from Harbor Freight a number of years ago for probably around $15...works very nice...it charges and then goes into the float stage holding the voltage. I've used it on my bikes as well as my truck battery.

[108625]

I had a similar problem with my '81 R100T (cleverly disguised as an S).
Are you still running the original starter? Would suggest inspecting and cleaning all your leads and connections first (the cheap stuff) and then if all else fails, this winter it might be time for a starter rebuild...It is twenty seven years old after all. The Bosch starters were made to be rebuilt, and it's worth doing when you look at the cost of an outright replacement. It's also peace of mind for those of us without kickstart backup.
Motorrad Electrik took care of mine a couple years ago for $75 plus shipping, (which was cheaper than some batteries).

Good luck,
Bob

[PGlaves]

I had a similar problem with my '81 R100T (cleverly disguised as an S).
Are you still running the original starter? Would suggest inspecting and cleaning all your leads and connections first (the cheap stuff) and then if all else fails, this winter it might be time for a starter rebuild...It is twenty seven years old after all. The Bosch starters were made to be rebuilt, and it's worth doing when you look at the cost of an outright replacement. It's also peace of mind for those of us without kickstart backup.
Motorrad Electrik took care of mine a couple years ago for $75 plus shipping, (which was cheaper than some batteries).

Good luck,
Bob

The R100 motors take a lot of amps to turn over with a non-geared direct drive starter. And, if the nose bearing gets just a little worn you can have internal drag in the starter motor. Lubricant goes away over time too.

New off the showroom floor starting could be troublesome unless the battery is completely up to snuff (whatever that old saying reeally means).

I think a thorough cleaning, checking, (rebuilding if needed) and lubrication of the starter motor is in order.

[AnnapolisAirhead]

Hey Guys
Got a 81 RS, have owned it since 91 and love the bike but have allways had a starting problem. If I ride it often it will allways start. I keep it on a battery tender and after a week or so it just won't turn over. In the 17 years I have had it I have put 4 or 5 batteries in it. Problem is alwas the same if the battery is new or old. Tender is suppose to keep the battery charged up but seems like it does not do the trick. Any Ideas on how to fix this problem would be great.
Thanks Brian
9842

Is the bike dual-plugged, by chance? My bike is, and the PO installed a Dyna Ignition booster to help with starting, even though its an electronic ignition.

Another thing the could be an interesting conversation is to call Rick at http://www.motoelekt.com/ and describe what's happening. If nothing else, he is very knowledgeable about the electics of ye ole airhead and you'll probably learn a lot. I did.:thumb

[8ninety8]

This spring I had similar problem, '74 R90S. Good battery, charged up, but slow cranking as if it had 14 to 1 compression! I was baffled until I read of how far the ground has to travel through the block to the electrics. Cleared that up with dedicated grounds eliminating any corrosion. Next, as others have said, cable ends were renewed by cutting off the green stuff and soldering and filing connectors shiney smooth. Also pulled starter, took it apart, checked brushes, lubed it. It spins like new.