Very Intermittent Stumble/Bogging, R75/5 1973

I've had three things over the years that mimic your symptoms:

1) Simple spark plug problem - new plugs, problem went away.

2) Most recently on my '78 R100 - one spark plug wire had a problem and for a few months it did as yours - intermittent cutting out - then, it went out competely - only ran on one cylinder.

3) Bad connection under my tank - front left side where there are several solenoids, etc. I found out one day when it was happening, I took my left hand and started reaching up under there and wiggling things, and voila!, I could get it to act up. I cleaned it all out, cleaned all connections, used dielectric grease, and even put a "shield" (made from a cut-up plastic milk jug) there to protect the area from direct wet weather & direct contact with brake fluid (master cylinder was up there and had shown signs of leaking) from previous owner. Never had that problem again.

lmo1131 said:

Well, the /5 has no "kill switch", so by "resetting" the ignition do you mean cycling (opening and closing) the switch clears the problem? There isn't a whole lot that can go wrong with that switch ( it's only half a jump ahead to twisting two wires together ), but what comes to mind is the "spring" contractor being weakened/deformed by the previous owner pounding the "key" into the switch.

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You have it right. Cycling the switch clears the problem.

I did examine the switch, but my key seems to be functioning OK. If anything, it's a bit of a bear to pull it up a stop to cut/cycle the ignition. I did have the bad habit of whacking the key in with the heel of my hand (gently but firmly), but after reading Duane's page I stopped that business. The keyway doesn't seem to be egged out, and all the locations selectable and toggle-able seem to engage positively. I did bend the lower of the brass contact arms on the switch itself up a wee bit, but perhaps it needs a wee bit more. I also cleaned up the contact with a little 2000 grit sandpaper.

SCBuckeye said:

I've had three things over the years that mimic your symptoms:

1) Simple spark plug problem - new plugs, problem went away.

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New plugs went in already - NGK BP6ES

SCBuckeye said:

2) Most recently on my '78 R100 - one spark plug wire had a problem and for a few months it did as yours - intermittent cutting out - then, it went out competely - only ran on one cylinder.

Click to expand...

New NGK plug wires from EME went in last week - spark feels better, while it lasts.

SCBuckeye said:

3) Bad connection under my tank - front left side where there are several solenoids, etc. I found out one day when it was happening, I took my left hand and started reaching up under there and wiggling things, and voila!, I could get it to act up. I cleaned it all out, cleaned all connections, used dielectric grease, and even put a "shield" (made from a cut-up plastic milk jug) there to protect the area from direct wet weather & direct contact with brake fluid (master cylinder was up there and had shown signs of leaking) from previous owner. Never had that problem again.

Click to expand...

My starter relay was in dreadful shape and the bike felt like one cylinder was cutting in and out, so I just tossed it and replaced it with a new unit. I used to be able to cure the rough running with a wiggle under there, but since replacing the relay the rough running has gone away, and I'm no longer able to induce it.