ignition coils

[Baldazar]

I'm working on a '79 R100RT with 70,000 miles. I've retorqued heads, adjusted the valves, changed out contacts, timed, rebuildt carbs, and synched them. My problem is when I start it it only seems to go on one cylinder for awhile, as it warms up the other cylinder catches. I'm thinking it might be my coils. I bought a used pair and when I went to swap them out I noticed the ones on my bike were Japanese 12 volt and the ones I was going to replace them with were Bosch 6 volt. My volt meter has been running under 12 volts. My battery doesn't have enough power to restart the bike if I have it idling very long. Have I been running the wrong coils all this time? :help

[20774]

Do I understand that you've been running two 12v coils in your bike? I'm certainly no electric guru, but that can't be good. You're bike is supposed to have to 6v coils, hooked in series, to give a total of 12v. I would definitely try the used coils, if they're the 6v variety.

The voltmeter running under 12v sounds like a separate charging issue. When the bike does run, what's the voltage measured with a known good voltmeter directly across the battery terminals, with the engine RPM around 3K or so? You should be seeing 13.5v or more preferrably near 14v. If not, then you'll need to do some additional troubleshooting to figure out where the problem lies.

[Baldazar]

Thankyou for telling me the correct voltage for the coils. I was lucky to have the other coils to replace them with.
Yes Kurt, you understand correctly. I didn't put those 2 12 volt coils in. One of the former owners must have. I switched over to the 6 volters and it didn't really change anything that I could see. I checked out the voltage across the battery terminals and it stayed right at 12 volts - whether I was at idle or 3000 rpm. I already changed out the voltage regulator to a solid state one. Any ideas why I'm not getting more than 12 volts at a higher rpm? :dunno

[20774]

How does the alternator light in the instrument pod work? Proper operation is: on bright when key is turned on but engine not started; light should go out as RPMs go above 1200-1500 RPM. If the light is burned out in the instrument pod, you won't get any charging...it is an important part of the charging path.

I'd say the two primary things that could be causing your problem are a bad voltage regulator or an open rotor. There is a test that bypasses the regulator...it jumpers two of the three connections together. If you then have charging at the battery (it can go as high as 15-16v so be careful), then the regulator is the problem. AutoZone (probably other stores) sells a generic regulator for 12v vehicles that will work. To test for an open rotor, you need a multimeter so you can measure the resistance across the slip rings, with the brushes lifted off or isolated from the rings. For your bike, the resistance should be about 3.4 ohms.

Another weak area can be the diode board, but that is harder to test. Also, the brushes could be hanging up in their holder or they could have worn down to the point where they're not making contact with the slip rings. The brushes are a wear item that need to be replaced once in a while.

Not sure if you've been warned, but when removing the front engine cover, always removing the connections to the negative side of the battery, either at the lower right transmission bolt or at the negative terminal of the battery. Make sure the negative terminal is completely isolated form the bike. There is a good possibility that when you removing the front cover, you can make contact with the diode board and short it out.

Rick at Motorrad Electrik can provide rewound rotors, diode boards, voltage regulators. He also sells a small booklet called Classic Boxer Charging...something handy to have, especially when out on the road. Stan Smith at Rocky Point Cycles has similar products.

Here's a link which provides some insight on testing the charging circuit:

http://www.geocities.com/wlsolutions/r100rs/electrics01.html

Another good website, along with others he references is found on Snowbum's site:

http://pweb.jps.net/~snowbum/trbleshootALT.htm

HTH...

[lkchris]

Having the correct coils is a good idea, but I wouldn't worry much about the bike running on one cylinder when it first starts.

This is MUCH more likely a fuel issue than an ignition issue, and perhaps the "choke" system in one carb isn't working the same as the other one.

What counts, of course, is how the bike runs when warmed up.

[Baldazar]

The generator light seems to function properly. As the RPM goes over 1200 RPM the light goes out. While the bike idles the gen lite is on. I changed out the volt reg to an electronic one and that didn't seem to change anything. I will check the brushes now and then I have a spare diode board I can swap out. I'll let you know how it goes.
Kurt S.
'79 R100RT
'05 Ducati S2R800
'80 Suzuki 550 SLR

[20774]

Have you performed any of the circuit tests? It seems that you're shotgunning the problem, and replacing things as you go. It would really be best to do some measurements and help narrow the problem down. I guess as a side benefit of this approach, you'll end up with a lot of good spare parts for next time...:laugh

Just my opinion...

[Baldazar]

I took out the front brush and it was over 10 mm long. Then I wedged folded pieces paper between the brushes and the rings. If my ohm meter was right the resistance between the rings was zero. I put it back together and my voltmeter showed I was generating 13.5 volts at 3000 RPM. Do I need to replace my rotar?:scratch

[20774]

Some confusing info...you measured 0 ohms resistance across the slip rings, provided you isolated them from the brushes properly. That's not a good reading at all... Then you put everything back together and you read 13.5v at 3K RPM...

Something does not compute...generally, you can't both of these at the same time!!

10mm on the brush sounds like it's short...I think 13mm is considered a minimum length. Actually, what the problem ends up being is the small snail spring that pushes the brush against the slip ring either gets hung up on the plastic brush holder (and exerts no pressure on the brush) or the spring gets over extended, resulting in smallish pressure on the brush.

Again, I'm confused by the 0 ohms on the rotor but yet you're getting decent charging...

[Baldazar]

Yeah Kurt, I don't understand it either. Maybe my ohm meter is out of whack. I'll get a better one and test it again. Those 12 volt coils probably didn't do my system any good either. I should be happy that I made 2 - 2 thousand mile trips with those in there. :drink

'79 R100RT
'05 Ducati S2R800
'80 Suzuki 550 SLR

[donbmw]

This is MUCH more likely a fuel issue than an ignition issue, and perhaps the "choke" system in one carb isn't working the same as the other one.

What counts, of course, is how the bike runs when warmed up.

I had the same thing on my 75 R90 when I bought it a few years ago. I was not as noticeable with warm weather but showed up more when the weather cooled. Check your float bowls were the fuel goes for the choke valves one of them is stopped up and will make not run right on one cylinder until the engine warms up.

Don

[sumran]

...rebuildt carbs, and synched them.

Did you have the starting problem before you rebuilt the carbs? I have seen a lot of posts where small adjustment or alignment issues were the cause of the problems similar to what you describe. I will be rebuilding mine in the coming months, so I will get to stumble through the wonderland of Bing.

It sounds like you have multiple issues, which makes it harder to determine the source. All of us that have adopted an airhead can relate to that!

In general, electrical components work better cold than hot. Fuel systems work better after warm-up than they do when cold. So, I agree with the earlier posts that fuel is more suspect than spark on your starting issue.

Something appears to have changed your output voltage. Your earlier post said you were only getting 12 volts and later you were getting 13.5. It sounds like the VR or Diode board may have changed something. Or perhaps disassembling and reassembling improved a bad connection.

[Baldazar]

Thank you all for the input. You guys gave me a good excuse to go out and buy a decent Sears voltmeter. The resistance across the rotor slip rings was 3.6 ohm. The voltage across the battery terminals at 3000 rpm was 13.7 volts. However my voltmeter on the bike reads 2 volts low. Other than the meter, my electrical seems to be okay.
IT IS A FUEL ISSUE!!:twirl I'll start another thread.
Thank you Kurt, Kent, Sumran, & Dan.

Kurt S.
'79 R100RT
'05 Ducati S2R800
'80 Suzuki 550 SLR