OT ~ perhaps, advice on ignition system

1) You are lucky that you don't have to deal with '70s Ducati electrics..... 2)Since you appear to have 2 independent systems, maybe there is a problem on the DC source side, is it electronically switched? 3) Run the MC in the dark, and lookout for corona, but that's a long shot.

martin

I haven't ruled out the LV side of things. The two systems don't fail exactly coincident with each other - one will go and the bike will stagger on for a few seconds then the other goes out.

The Clymer manual calls it a CDI ignition system, but it is only supplied with 12 volts and the switching modules are only ~1 cubic inch - I doubt they had any real CDI system back then (and that small?) Modules are large enough for a power transistor or two and a cap.

I'll give that a try - I'm grasping at straws now.

I did break down and replaced the plug connectors and wires - that has really made a difference in acceleration and idling so maybe that is it . . . The old plug caps measured between 6-9 K ohm resistance and all the new ones are exactly 5 K (5K is what it should be).

I've had a few bikes with some pretty horrible electrics - a Gilera in ~'66 and Triumph in '70. Gilera - the engine would die if the stop light was blown out and you braked, side draft carb float would cause it to accelerate in left hand turns and slow in right turns - Trumpet caps would die and the engine would make a burbling sound when accelerating. Neither had headlights worth a damn. Neither bike was much good above 8,000 feet in altitude.

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Argh, I rememer dirtbiking just after new year, in the snow in Derbyshire on a Montesa, and the magneto packed up. It wasn't even Lucas, I was towed 8 Km across the rough, including a river bed, in the dark. Not fun

martin

Maybe not an electronic problem? Some kind of vaporlock in the fuel system piping comes to mind as a possibility.

Ed

The temperature may drop a little in rain if anything.

I did consider a fuel problem - sprayed water on the seals between the carbs and cylinders so it isn't sucking some water in there. Runs a little lean, but I haven't re jetted since replacing the exhaust.

Possible that the water on the fuel cap is making the tank vapor tight. There's a large rubber washer that is spring loaded to press against the tank opening. It must be a perfect seal it always looks like polished steel - no rust. Possible that a tiny amount of water is just viscous enough completely seal the tank and it tries to pull a vacuum - that would account for all the symptoms - and something I should be able to check with a water bottle and some driving.

There are four carbs one for each cylinder - I wouldn't expect them all to drop out together - but this isn't like running out of gas, there's always a little in the tank that sloshes into the fuel tube - a vacuum would mean no carb gets a taste of gas once the vacuum forms. Rain cooling the tank would also lower the vapor pressure. (and it fits all the other symptoms very well)

one more thing to try . . .

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Unlikely. Air box opening faces aft and has no leaks. It will tolerate a lot of sprayed water before it starts running rough. I sprayed water everywhere even the places that shouldn't cause problems

- fuse box, headlight nacelle, anywhere wires run or air moves.

The symptoms when it dies are rather sudden - just like switching off the ignition. I sometimes lose one pair of cylinders first then the other. Each (brand new) ignition coil feeds two cylinders - one spark is wasted firing a cylinder that is not on the compression stroke.

The coil side has compression ferrules,of rubber, that grip and waterproof the HV wire. The plug caps only have rubber boots - but have worked well enough in the past.

When I replaced the caps and wire I used some thick silicone grease that is supposed to be for "spark plug boot release."

Maybe there's more than one cause for the problem. Maybe I should be dealing with the lean running . . . that and a weak spark, high moisture in the air . . .

Dies just like switching off the ignition so that's where I'm concentrating.

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I'm late to the discussion, so this may be a repeated question...

Electronic ignition? I've had those modules in the distributor fail with the symptom of like you just momentarily just turned it off.

Particularly Fords... which I placed on my "Do Not Purchase" list almost exactly 30 years ago... scary as hell, tooting down the freeway, suddenly no power, slows then resumes ignition :-(

...Jim Thompson

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