Intermittent ignition problems and such.

Lately my 72 Combat has been having a slight ignition problem, and it just got really bad yesterday. Once in a while cruising in top gear, the right cylinder decides to stop running, the only way to get it back on again is to pull in the clutch and rev to 5,000 RPM.

Yesterday, it did the same thing, but it started to cut out on both cylinders, VERY BADLY. Feed it more throttle and it just acts as if the ignition switch is off, then at about 2,000 rpm it cuts back on again for 4-5 seconds, then back off again.... this went on for about 3 miles. The only way I made it home was to keep it at 1/4 throttle and 5,000 rpm, still intermittent though.

It would clear up for 10-20 seconds, then start acting up again. Got it home and had a look at a few things, nothing really obvious. The pickup plate under the points cover, one of the wires was a bit nasty looking, but it was still fully attached, it seems to be missing a few strands, I will try and remedy that and see if it helps.

After I let it sit for a few hours, I went for a another ride, it went fine untill 3rd gear at about 5,000 rpm and it would start playing single cylinder again.

And I have been having problems with lighting and blinkers lately too. then i found the fiberglass tank is leaking from the side of it.. everything hit the fan at once, perfect

Anyways, what should I be looking for?

Are you running a Boyer ? It is probably a combination of low battery volts and poor connections. An oxidised connection or a break inside the insulation are enough.

If you don't want to be constantly chasing problems, the best advice is probably a re-wire and a new battery.

Yeah, I forgot to add that I have a Boyer on it. The battery is brand new.

Where should I start looking for these poor connections?

The boyer box is probably on its way out isn't it?

72Fastback said:

Yeah, I forgot to add that I have a Boyer on it. The battery is brand new.

Where should I start looking for these poor connections?

The boyer box is probably on its way out isn't it?

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Probably not in my experience.

A new battery is not a guarantee of a good one. Do you have a multimeter ?

The Boyer needs a good feed. It might be a good idea to by-pass everything (switch included as that could be the problem) and run a cable from the battery to the Boyer. The other crucial area is the wiring from the pick-up to the black box. It will typically break where it passes through the timing chest. I use moulded two-core mains cable as I find that the outer casing helps delay this sort of problem better than two loose wires fed through a sleeve.

Yes I have a multimeter. The battery is around 12.8 volts right now.

How do you get to the wires that go through the timing chest?

Have you tried measuring at the ignition switch and at the Boyer box ? This won't necessarily tell you anything as your fault is still intermittent at this stage.

In order to remove the wiring in the timing chest, you'll need to remove the Boyer back plate. Best to scratch a line to aid reassembly. To be honest, I would just replace it anyway. It should really be a maintenance item.

There should be a long thin grommet/ sleeve in the timing chest and it can be a bit of a fiddle to pull through with both bullets on (but usually one pulls off showing the bad connection that was causing the problem ! )

I recently had a similar problem with a bike that had an all new wirng harness and good battery. The fault was in the Lucas ignition switch. I bypassed the switch with a jumper wire and the problem was solved.

worntorn said:

I recently had a similar problem with a bike that had an all new wirng harness and good battery. The fault was in the Lucas ignition switch. I bypassed the switch with a jumper wire and the problem was solved.

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It's a good idea to take the switch/kill switch apart and clean same...it might be corroded and needs to be cleaned. I was surprized to see how small a contact there is in the switch...All the juice to your ignition goes through this switch, so if it's corroded, it can cause problems for your ignition. I tossed the Boyer and went back to points...

My kill switch does not do anything at all on the bike. Is it possible for it to be unhooked and still let the bike run?

I will have to dig into that switch tomorrow and check where my wires go, and whether they are hooked up or not.

Thanks for the help so far

If you run a kill switch on an electric ignition equipped Commando you can carry a short jumper wire in the head light shell to bypass the kill switch as necessary and it will be necessary believe me. Ride in the rain for three hours to find out why. So learn the circuit colors build the jumper and stow it in the shell all can all be done inside the head light shell on the side of the road. You should also have stowed along the loom a power wire to jump power to the ignition module from the battery kept on the bike. It just makes sense with the known faults in this old system.
When you quote a battery test voltage did you know that you must first run the head light for 3 minutes and than without turning it off test the battery? Any other test means nothing. You have to remove the surface charge from the battery to know what the bike is accurately getting running down the road. Anything under 12.4 volts is suspect for an E.I.

72Fastback said:

My kill switch does not do anything at all on the bike. Is it possible for it to be unhooked and still let the bike run?

I will have to dig into that switch tomorrow and check where my wires go, and whether they are hooked up or not.

Thanks for the help so far

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Sounds like someone by passed the Kill Switch, which can be done...
Trace your ignition wires from the Points/Boyer to see. Someone may have spliced into the main wiring loom to bypass the switch...Be careful taking the kill switch apart...parts will fly and fall out if you're not....

"The Boyer needs a good feed. It might be a good idea to by-pass everything (switch included as that could be the problem) and run a cable from the battery to the Boyer."

Could you please elaborate on this quote? Would it be from the possitive lead from the battery? Which wire on the black box? Do you have to disconnect anything from the ignition? Any help appreciated. thanks, jerome oh yea, how do you enter a quote?

jerome said:

"The Boyer needs a good feed. It might be a good idea to by-pass everything (switch included as that could be the problem) and run a cable from the battery to the Boyer."

Could you please elaborate on this quote? Would it be from the possitive lead from the battery? Which wire on the black box? Do you have to disconnect anything from the ignition? Any help appreciated. thanks, jerome oh yea, how do you enter a quote?

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Quoting's easy - just click on the blue quote box and space out anything that you don't want.

If your Commando is standard +ve earth then NO not the +ve lead from the battery ! Simply run an extra cable from the battery -ve to the connection on the white wire close to the Boyer. You shouldn't need to disconnect anything else.

If it's a Mark 111 Boyer (ignition, not Commando) then the wiring is marked on the black box. No harm in also trying substitution on the other wires such as to the stator.

Well, I got out the volt meter and did some testing. On the timing stator/rotor, the black/white wire had 11.43 volts, while the black/yellow wire had 11.33 volts, does this sound weird or is it ok? I may have got the wire colors switched, but you get the point. I had one voltmeter lead on the engine head, and then checked each wire. At this same time, the power take off socket read 12 volts I believe. I guess I will just test ride the bike, if I have the ignition problem again, I will run the alternate wire from the battery to the white wire on the boyer?

There's your problem. Too low for a Boyer. You've either got a battery problem, or a voltage drop between battery and Boyer.

You should have your battery load-tested (or do a quick and dirty test yourself - run headlights for two minutes then check voltage across battery terminals). Should be at least 12.5 or so I would think.

If battery okay, you need to get a multimeter and figure out where you're dropping voltage. If you don't know how to do such a test, I or someone else here can tell you, or google "voltage drop test'; I'm sure there are tutorials out there. It's simplicity itself, and a very valuable skill - essential for any Britbike owner, and darned worthwhile for any bike owner.

Fastback,
Do you mean the Boyer Timing stator or the alternator?

Cash

The timing stator, underneath the round timing cover. I will check again tonight, just to confirm my voltage readings.

Where could I lose voltage between the boyer and the stator, all that is in there is a set of connecters?

Could the connecters be bad, I pulled them apart and cleaned a bit of corrosion off of them, but thats it. Hopefully there is nothing wrong with the Boyer box.

fastback, old britts web site has a technical section and in that section they have a very methodical boyer troubleshoot section in there. i suspect i am having a simalar problem, but mine is at low speed, getting some popping, backfireing, uneven running. runs almost perfect mid throttle on. i found my connections in the timming cover poor, and have since soldered them. i suspect some wireing issues, since i had to move my coil cluster when i removed my head, and has not run the same since? good luck, when i have success i will report. jerome

Well, I fixed some old connections and resoldered a few things here and there, and rode the bike for 95 miles today, and everything was perfect!! I'm loving it!

For some odd reason it feels like it runs noticeably better as well. Maybe thats because I took off my luggage rack and blinkers, less weight is less weight, after all. :wink:

Jerome- good luck with getting your problems sorted out, if anyone can help you, its these guys here! Thank all of you guys for your help.