New Commando Owner In Need Of Advice

I'm a relatively new Commando owner (1973 850) and I've been avidly reading my way through Access Norton after discovering the forum via Google. I bought the bike a few weeks ago after having wanted one forever, and today I had my first mechanical gremlin pop up.

I went through the usual procedure and on the kickstart there was an almighty POP sound, followed by some smoke through the carburettor's air filter. I thought it might have just been a backfire so I attempted to kickstart it three more times, and each time it kicked back hard with more smoke visible from the air filter.

I wanted to ask what could be causing this and how I can best troubleshoot it? It's currently fitted with a stock ignition, the original Amals, the original coils and a battery that's seen better days. I plan on replacing all of the above over the next week or so.

Thanks for your time!

Branch, new members always welcome.

Can you tell us more about the bike.
Has it run recently or been sitting for a long time?
Did you do anything that could have affected the timing since kickback sounds like ignition failing to retard?
When it banged did it also kick back which also sounds like a timing issue?
New plugs?
Fresh gas?
Carbs clean especially if Amals all the small orifices.
If not run for a while may have corrosion in wiring, at switch, kill switch, others causing bad spark
Kicking it over with plugs out and plug held to head do you see a decent regular spark?

Without knowing more I'd take a close look at ignition for corrosion, point clearances, and make sure static timing ok.
As you go forward with the bike a very popular upgrade is an electronic ignition which reduces kickback issue, stays in tune and avoids the common problem of wear in the points system known to cause irregular spark. A number of decent choices but Pazon Sure Fire is not very expensive and I've personally had very good service with one.

I'm sure others will add other ideas.

Whatever it takes you'll find it very worth while when the bike is all sorted out and you get out on the road.

You mention that the battery is tired. What voltage is it showing?
Insufficient charge in the battery can cause back firing, though points ignition is more tolerant of<12 volts than older EI ignitions are.


Glen

Thanks for your replies, I was researching this further on this forum and decided to try what another guy had tried who had a similar issue. I turned off the ignition and cycled the kickstarter a few times to clear the cylinders. After this is started first kick. It looks like I may have flooded it and caused a misfire - it was my first time hearing one and feeling kickback so I was a little concerned!

RX7171 - Thanks for mentioning the ignition, I've actually got one on they way by Tri-Spark with a modern coil and new plugs/leads. I'll also get a new battery. The electrical systems on the bike look like one of the previous owners might have bodged it more than once so I'm tempted to look into fitting a new wiring loom, although the complexity of that task may be a little out of my reach for now.

Glen - Thanks for that, this may be a stupid question but how can I check the voltage?

FWIW, a points system is totally unaffected by voltage as far as timing issues. The timing is totally mechanical so with points, there is either enough voltage to fire the plugs or there isn't. However, the oem advance is known to stick at full or partial advance if the advance unit is not given periodic maintenance which can cause erratic operation when kickstarting - being stuck in the advanced mode (kickback/backfire) sometimes and not other times. Obviously, incorrect initial timing will produce incorrect advance…as it will with an electronic system.

I think the Trispark is a good choice. Of the commonly available E-systems, it is the one that most closely duplicates the original points/mechanical advance curve which is the optimum setup for a street bike. I removed the Boyer that was on my bike when I bought it in '06 and went back to oem for better overall performance and I had no intent of ever going to an E-system. But when the Trispark showed up, I decided to give it a try based on the duplication of the oem advance curve. It's been on the bike for 6 years and has been working flawlessly.

Even with points, when the voltage gets down back firing occurs, at least it does with my system, (Commando points ignition on a vincent) With that bike when the battery is near dead, it's kick,kick, kick, boom. With Battery up it starts in one kick almost every time.
You can check the voltage with a multimeter set for DC voltage measurement. They are available at most any auto parts store.

Glen

I find that mine is liable to kick back if I have the throttle open too wide.

>>The electrical systems on the bike look like one of the previous owners might have bodged it more than once so I'm tempted to look into fitting a new wiring loom<<

Best approach is get a new loom and as old one is removed install new alongside and switch out each connection point new with old.
Repair manual has wiring diagram which is helpful.
Standard looms had extra wires that only related to the police model of bike with its radio, flashing lights, etc which make for quite a few uneeded wires.
However I believe the loom sold by Commando Specialties leaves out those extra wires. You may want to call and confirm if thinking of buying from them. The wire colors should match originals.

rx7171 - I've been wondering about this, I'd love to get a brand new loom as I can see that I'll have electrical problems (especially in the rain) otherwise.

Welcome & good luck. Nice looking bike, what ocean is that your parked next to??

Branch said:

rx7171 - I've been wondering about this, I'd love to get a brand new loom as I can see that I'll have electrical problems (especially in the rain) otherwise.

Click to expand...

The largest problem with the stock wiring is the connectors. Nothing really wrong with the wire as long as it hasn't been rubbed through the insulation or a previous owner hasn't gone artistic. The connectors have a "C" shaped metal inside the plastic tube that breaks with age and use. I check and replace worn connectors each winter and have cleaned up past owners mistakes keeping to original wire colors. No electrical problems on my machine.

Removing the wiring and replacing it is not as big a job as it appears. Remove the gas tank, seat, side covers, headlight and you should be able to access everything you need. I find replacing the Lucas bullet connectors with modern ones really helps. Make sure you have good grounds especially to the engine as it is suspended by the isolastics and they don't make a very good ground. Study the wiring diagram with the bike in front of you and it will all start to make sense after awhile.