Need to perform an electrical exorcism

[rl900]

My '81 R65 is possessed!  It starts easily, idles nicely, performs well.  Then after about a mile the tachometer begins to swing wildly, it misfires, often banging loudly and shooting a flame out one or other muffler.  Sometimes it dies.  Starts up again fairly easily, but in a few hundred feet begins to miss again.  It seems like this behavior is slightly preceded by the tach needle suddenly jumping up by 2 or 3 thousand rpm (engine steady).

Wiggling the ignition key or the kill switch seems to have no effect.  Not surprising, as I can't see how that could affect the tach or the timing.

The bike has about 5K original miles and has spent much of its time in a shed in Florida before I got it.  I plan to start checking for corroded connections, but wondered if the collective brain trust recognized a tell tale component failure by these symptoms?

[Bob_Roller]

I had my bike do the same thing about 13 years ago, you're on the correct path with going through all of the electrical connectors .

I went through mine, don't know which one was causing the problem, but since I cleaned and made sure all of the pins in the connectors weren't backing out, and all of the connector halves fully engaged with each other, haven't had the problem since .

If you have a connector that doesn't feel like it's going to stay together, try using a small ty-wrap on the connector to secure it .

[nhmaf]

I agree with Bob - I also think that you should pay particular attention to the wires that go to - or are connected with the igntion parts ICU, coil, etc.  The reason I say this is:
1.  The tachometer is connected to the coil and gets its signal from there - and you indicated it behaved erratically.
2. If you stop getting spark to a cylinder but the other cylinder keeps the engine running (though not well) you will continue to pump gas&air through the nonworking cylinder and exhaust pipe - and then when a spark does finally come around - that is when you get the "bazooka effect" of flame and noise.

Also, are you still running the original coil, or has it been replaced?

[Bob_Roller]

When my bike started acting up, I was doing a lot of night riding, when this occurred, I lost the entire electrical system, all of lights went out, and normally would come back on in a few seconds, once I had to pull off onto the shoulder of the road and after a minute or two, everything worked fine .

Good chance you're losing more than just ignition .

[rl900]

It is the original coil.

I'll start cleaning/checking connections tonight.  I wanted to make sure I wasn't overlooking something obvious.

Thanks, guys.

[Bob_Roller]

It would probably be in your best interests to replace the original black and gray ignition coil when you can get around to it .

It's a known problematic part, has earned the name 'crack-o-matic coil', the plastic case cracks around where the laminate metal core goes through the plastic case .

Most notably it causes ignition problems in wet/damp weather .

A popular aftermarket replacement is the Dyna 'brown' coil for the electronic ignition equipped bikes .

If you have ignition leads with the metal caps at the spark plugs, wouldn't be a bad idea to replace those as well, they're probably original as well .

[DgM]

Dollars for donuts it's your coil.

[montmil]

I like donuts! The OEM gray n' black coil on my 1981 showed tiny little cracks on the end. Had to remove the coil and wipe it clean before the cracks were visible. Bag dog, no biscuit.

Call Rick Jones at Motorrad Elektrik. He's the Airhead exorcist.
http://www.motoelekt.com/index.html

For both my R65s, I buy NGK plugs, caps and ignition wires from a very economical source in Florida.
http://www.mikesxs.net/

[rl900]

Yep, Had to wipe the coil down with solvent to get all the dust and grunge off, but sure enough, cracks on the end.

This began to make sense with the tach suddenly going to 4000 rpm at idle while the engine began to stumble.

You guys saved me a lot of time tracking this down.  New brown Dyna coil and bracket on its way.

The bike already has NGK caps and good cables.

I'm still learning about the airhead.  Heck, I'm still learning about Nortons after owning and building them for 37 years.  I guess I'm a slow learner.

Thanks again.

[montmil]

...Heck, I'm still learning about Nortons after owning and building them for 37 years...

Oooh! Lord Lucas, the Prince of Darkness lives.

Monte

[rl900]

Got the brown Dyna coil on Saturday.  Mounting was a snap.

All demons appear to have been exorcised!

Thanks for the help.