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jchen
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Joined: 07/07/2015
Posts: 17

I purchased a fantastic r75/5 about six months ago and had it overhauled by the local BMW dealer and it's been working like a dream. The last ride and my ride this morning, it has been 'coughing' a lot, in particular in the higher gears. I though it was that I was low on gas (just filled up) but no dice. I also notice that the battery charger light is flickering a bit and now is seldom lit (it generally is lit a good portion of the ride). I trickle charge at night but didn't last night. I can't imagine this is the symptom of an undercharged battery, but is there an obvious culprit (? I was assuming carburetor?). THANKS.

schrader7032
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VBMWMO #7032
San Antonio, TX
Joined: 10/27/2006
Posts: 6622
I've often heard that carb

I've often heard that carb problems are often electrical in nature. You should figure out the situation with the generator light...the bulb must work by being on with the ignition on (bike not started) and then go out when the RPMs get above 1500 or so. If it doesn't do that, then you probably have an alternator issue. Start the bike...does it start OK on the electric starter?...and measure the voltage across the battery terminals with the engine is revving say 3000 to 4000 RPM...it should get to near 14v. If not, then the alternator or some part of the charging system has failed.

Not exactly sure what you mean by coughing. And it runs OK in lower gears and lower speeds? Could be your timing is way off. Could be that your coils are breaking down.

As for the carbs, it could be that there is insufficient fuel in the float bowls and at higher speeds, it can't be pulled up by the carb venturi and sucked into the engine. Could be that the gas tank is not venting and allowing the fuel to flow to the carbs...when it coughs again, try safely cracking the gas cap and see if the problem goes away. One symptom of not being able to maintain steady speed at higher RPMs is torn diaphragms in the carb tops. Might be time for a carb rebuild.

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Kurt in S.A.
'78 R100/7 '69 R69S '52 R25/2

mark_weiss
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Arizona
Joined: 11/17/2013
Posts: 173
It is unlikely to be a

It is unlikely to be a charging system issue, unless the battery is low enough to create a misfire. Not too common if the electric starter works.

More likely would be insufficient valve clearance or an ignition system wire shorting to ground. Could be the wire to the points or one of the connections at the coils.

Could also be a bent contact at the main switch. When you press the key all of the way in, does it readily make contact or do you have to fiddle with the key a bit to get everything to turn on? I've seen a bent main contact that was just barely bringing the switch points together. Fortunately, that problem is very easy to fix.

Mark

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Mark
qualitycycleservice.com

jchen
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Joined: 07/07/2015
Posts: 17
Sometimes the simplest solutions are the right ones

Well 6 months later and you were right on the money. It's a bad contact. What's the best way to fix that?

mark_weiss
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Arizona
Joined: 11/17/2013
Posts: 173
If it is the main contact for

If it is the main contact for the ignition switch, get a bright light and study how the contact works when you insert the key and press it fully home. Next, with the battery disconnected, gradually bend the main blade of the switch so that the contacts are closer together. Do this gradually and without kinking the blade. With the contact spacing reduced, inserting the key will make firmer contact.

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Mark
qualitycycleservice.com

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