Electrical or fuel conundrum

Heading home from work the other day, on the slip road joining the dual (freeway) the bike (750 Commando) started to miss and run sporadically very rough. I had about 5 miles to go so my immediate reaction was to try and nurse it home, it would have been dangerous to stop and I figured I wouldn't get it started. During the five miles I tried to figure out what the problem might be, remembering the old adage that 90% of fuel problems are electrical and visa versa. Managed to get it home by which time it was really bad. Pulled in, smell of petrol, fuel pissing out the left carb, the drain plug was missing.
So a no brainer, fuel. Fixed it, bike started no problem, it just wouldn't go when ridden up the road. Checked the plugs, left plug no continuity, swopped to new, still wouldn't go although started fine. Checked carbs to make sure mains hadn't backed off or anything else, all good, tank off looked at the coils all wiring in place. Multi meter out checked continuity of HT and primary and secondary all good. But then there it was, the coil to coil wire had broken inside the insulated spade connector on the left coil (I don't like those things), was held being in place by the plastic so looked good but was making intermittent contact with vibration.
Nearly a black swan event of a fuel and an electrical problem coming together..........and poof! Commandos don't you just love 'em.

This sort of spade?

Yeah they’re no good.

The problem with these spade connectors is not so much in the connectors, but people using inferior crimping tools.
Good quality crimping tools are essential, (but donot come cheap).

Triton Thrasher said:

This sort of spade?

Yeah they’re no good.

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I have never had one of these connectors fail yet as I use the right crimping tool a ratchet crimping tool is worth every cent and a good investment for any workshop.

Ashley

With ALL crimp type connectors, DO NOT SOLDER the wire end first, then crimp.

The soft solder will creep under the compressive load, and the joint will become loose in a matter of months.

Crimp, then solder is OK.

Slick

Peter R said:

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Ash man said:

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It’s good that you guys reckon you can make pre-insulated crimps work, but people are always going to use the tool that comes with the kit.

Triton Thrasher said:

It’s good that you guys reckon you can make pre-insulated crimps work, but people are always going to use the tool that comes with the kit.

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I reckon TT does not like pre-insulated connectors, and neither do I. I usually remove the nylon jacket from a pre-insulated connector (if I am forced to use one) and crimp (with a good tool), then insulate with shrink tubing.

Slick

Triton Thrasher said:

This sort of spade?

Yeah they’re no good.

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Yep those one, I like the clear plastic covers. People are right of course, use the correct (expensive) tools. Seems like there are ratchet crimpers for each variety of connector.

You had a missing drain plug and a broken coil wire!!
...and survived!
Go and buy yourself a lotto ticket!

Good detective work there. The double whammy of fuel and electrical issues at the same time would cripple a lesser man's commando for a long time......

FWIW, there is no "OLD adage" that 90 percent of fuel problems are electrical and 90 percent of electrical problems are fuel"

The REAL (and accurate) old adage is: "90 percent of all carburetor problems are electrical." It was an "old adage" because it was true and based on reality. People commonly blamed carbs for what was almost always electrical (ignition) issues. I have no clue when it morphed into it's present state as more of a joke than a useful principle. I guess when carburetors went away?

I had a drain plug fall out and made it home as well. Fuel everywhere! A couple more miles and I would have been out of gas. I drilled them and safety wired them together.

45 years of owning British motorcycles I have never had a carb drain plug come loose or even fall out in all that time, I brought a 79 Bonnie off my brother in law that sat for many years and I took my battery over to start it after putting fuel in it and it started after 2 or 3 kicks and I brought it cheap, when I got it home the next day it wouldn't fire the main wire to the coil only had one stran of wire connected to the coil that broke that one stran was enough to start it the day before, unreal, I only kept that Bonnie for one year as every time I rode it something else broke or fell off, it was a jinks bike, I spent more time fixing it than riding it, the brother in law brought it back off me but it costed him more from all the repairs/replacement parts I done to it, then he let it sit again without riding it then sold it to a friend of his who ended up rebuilding the whole bike.

Ashley

texasSlick said:

With ALL crimp type connectors, DO NOT SOLDER the wire end first, then crimp.

The soft solder will creep under the compressive load, and the joint will become loose in a matter of months.

Crimp, then solder is OK.

Slick

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Soldering a crimped connector can introduce a high resistance joint and the heat loosen the clamping/support of the connector to the wire's insulation.There are a number of different types and quality of crimp/compression connectors, the better type have the inner metal connector that crimps both the wire and the wire's insulation with the outer connectors insulation .This type of connector clamps/supports both the wire and its insulation. Another option is to use marine crimp connectors that have a contained sealing 'grease' to stop oxidation of both the wire and the connector . An alternative is to apply a product such as NO-OX-ID type 'A'. This product protects the wire and connector from oxidation and maintains conductivity to the freshly stripped ' bright 'wire ( do not cut into wire strands ) and then crimp using the correct jaws in the ratchet terminal crimping tool . The wire stipping can be over enthusiastic and the wire strands are damaged and provide a point of future failure when stressed /flexed . Also important to use the correct size of connector for the size of wire to avoid a compromised termination .

Ditto the don't solder a crimped connection. It's a big no no in aircraft as the solder stiffens the joint and makes it susceptable to fatigue fractures. Of course aircraft wire is tinned. If you're making your own harness or repairing one good quality Ancor tinned cable is available in various colors at West Marine in the US by the foot. Some Chandlery near you may have the same. Buy the best terminals you can find. I'm partial to the terminals with built-in heat shrink. They're expensive and tend to be of good quality. Use a ratchet tool.

Timely frequent subject, for me, as well. But my issues I've found should have pointed to the problem(s) being conclusive.
However that is not the case. Just getting my '69 Fastback of 43 years of ownership back on the road and
sorted out. It had last run 6 years ago, so updates done now that it had needed then. Good spark, dressed
the points, didn't replace, It fired 1st kick 3 weeks ago tonight, late in the shop and always has
been a 1 or 2 kicker. I had been through the carbs,
all good. New tires, tended to wheel bearings, oil change, fork gaiters, forks serviced, etc. Been riding it,
and man, I sure have missed the Norton growl... runnin' great. Until last weekend, developed a miss,
and I too was able to limp it home. Diagnosed intermittent spark on the R cylinder. changed out the coil
as I had a new one (although it has plus and minus, and my old coil there is a number 1 on one post and 15 on
the other, single wire was to the 1 and a two wire connector to the 15; I wired the single to the minus and the two
wire to the +) Good consistent spark, fired it up and was running the same...damn. Switched the post
wires..., damn, running the same Moved on to carbs,
dropped the bowls, and noticed main jet threads were showing !, sure enough loose.. well that will fix it...
NOPE. I even confirmed the chokes slides were still all the way open as they had been disconnected years ago, yep, all the way open. Blew out all the passages with compressed air, everything's open, clear. Slides are synced. Running better, but rough. I put in the new points, checked the valves, they are right on, and all
of them are moving. Strong compression with finger test. I did notice when I pulled the R side plug
wire I got a bit of a shock. So I pulled the long wire off my HD Shovelhead and tried it. No change,
but I'm thinking it's not plugging all the way into the coil, and same with a wire from a car I tried. Of course
the original wires were steel... It's not so much a miss, just running roughly.
I don't know if that's what it's down to or not, but about ready to pull the few hairs I have left out of
my 60 year old skull !!!! As I said the thing's I've corrected should be conclusive.....I can't leave it
alone til I've solved it, but I'm shot. After I these years with it I know it pretty well, I thought... Any idea's ?

I reckon your missing drain plug caused misfiring and increased vibration, and that vibration was the ‘straw that broke the camels back’ for your wire. I say this cos I have an almost pathological aversion to believing in coincidences!

I have an almost pathological aversion to pre insulated connectors too...

I would STRONGLY suggest going through your wiring and removing all such horrid pre insulated connectors. They really have no place on a motorcycle at all.

I must be ‘connector-ist’ or sumthin, cos whenever I see them on a bike I just see ‘botch’ and struggle not to just assume the whole rest of the bike is a ‘botch’ too !

Fast Eddie said:

I reckon your missing drain plug caused misfiring and increased vibration, and that vibration was the ‘straw that broke the camels back’ for your wire. I say this cos I have an almost pathological aversion to believing in coincidences!

I have an almost pathological aversion to pre insulated connectors too...

I would STRONGLY suggest going through your wiring and removing all such horrid pre insulated connectors. They really have no place on a motorcycle at all.

I must be ‘connector-ist’ or sumthin, cos whenever I see them on a bike I just see ‘botch’ and struggle not to just assume the whole rest of the bike is a ‘botch’ too !

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I think you might almost be right FE. When I relive what happened I think the wire broke first then the drain plug fell out for the reason you suggest. I agree about those connectors, they just happened to be what I had when I replaced the bridge wire between the coils. I use superseal, bullets or uninsulated with clear sleeves normally. I have the (very expensive crimpers) for all 3. I have also used some connectors normally used in RC models on the race bike. Found these when buying a RC battery for the ignition.

Aren’t RC connectors gold plated for Max conductivity?

Fast Eddie said:

Aren’t RC connectors gold plated for Max conductivity?

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Now you mention it they do have a gold finish, I assumed some alloy. They solder well whatever it is.