My Commando won't start

TheCounty said:
Any chance choke is not partially on.
I've been riding a 750 since 1991 in Canada. Never needed choke even at freezing, just a smidge longer on the tickler. Removed choke system & packed away. Possibly you're just to rich on a cold start, & plugs wetting up at first kick.
Best of luck
Click to expand...
The bike does not have chokes fitted. There was very little wetting of the plugs before I cleaned the carbs. They are wetter now after a couple of kicks.
 
Ever try cold with an intial shot of ether?
Bad fuel a reality in Canada, so bad that fresh premium from Name-Brand station would not fire in an injected car recently. Ether is a quick check to see if you should drain & refuel. Good carb clean & adjust won't help if fuel is bad.
Best of luck. Cheers
 
Another point I noted in your original description...a modern rectifier and a zener? Please describe this more....most folks move to a reg/rec....which fully replaced the zener.
 
What carbs do you have?

You say you cleaned out the jets, but the pilot jets are very difficult to clean on mk1 concentrics, some would say impossible without modification (search Old Brits guides for this).

Carbs also wear: slides, bodies, needles, needle jets all wear.

50 plus year old carbs WILL be worn. They could also have none standard jets / needles.

So, stripping the carbs to verify what slides, needles, spray tubes, jets you have, and what condition they are in, is a needed step.

It’s similar with the ign: wires, black boxes, pick up plates, HT leads, plug caps, etc can all suffer age / use related degradation.

So… when it comes to problem solving on a 50 plus year old bike like this, it is often NOT a case of searching for one finite root cause, it is often a case of several contributory causes (each one quite minor alone) combining to cause your symptoms. Therefore, what is required is to ‘confirm / revert to standard’ with the relevant systems / parts.

You DO have one known issue, the coils. IMO you are pissing in the wind trying to work around this. You need a good spark, so having the correct coils is a real no brainer.

Then, you need to calmly, methodically, go through and rule out all of the potential contributory causes mentioned above and confirm / revert to standard condition, which means repairing or replacing parts that are incorrect, suspect or worn.

If it were me, and I wanted a good starting and good running bike (and some will disagree with this), I’d put a Tri Spark ign and two new Tri Spark coils on it straight away.

Then I’d strip the carbs as mentioned above and make a decision on them. Meaning, if they’re good and just need a clean then I’d use them. If the bodies are worn, or if I had to spend a lot of money on new parts for them, I would bin them and fit new Premiers.

I know you’re trying not to waste money, but I assume you don’t want to waste a lot of time either right, and want a nice starting and running bike? At the end of the day, a new Tri Spark and a pair of Premier carbs really does provide an easy starting, well running machine (provided the rest of it is ok of course). If you’re planning on keeping it and enjoying it for many years, it’s really not a big investment to make on a bike and is a quick way of ruling out dozens of potential issues.

By the way… @SteveBorland is based in Denmark and has (or had) a pair of Premier carbs for sale… they’d be much cheaper to ship than new ones from England I imagine.
 
Last edited:
I think if the plugs are wet you have an ignition problem. If the 12volt coils are connected in series they will be working on half the voltage they were designed for. I would connect them in parallel and see if it then starts. Even if the resistance is then below the recommended for the ignition it would prove a point and mean buying two 6 volt coils would be worthwhile.
 
TheCounty said:
Ever try cold with an intial shot of ether?
Bad fuel a reality in Canada, so bad that fresh premium from Name-Brand station would not fire in an injected car recently. Ether is a quick check to see if you should drain & refuel. Good carb clean & adjust won't help if fuel is bad.
Best of luck.
Click to expand...
I have drained the tank and carbs. For the next try I will use new fuel.
Tornado said:
Another point I noted in your original description...a modern rectifier and a zener? Please describe this more....most folks move to a reg/rec....which fully replaced the zener.
Click to expand...
The rectifier is this type. The Zener is OEM.
Fast Eddie said:
Are you flooding the carbs correctly prior to starting?
Click to expand...
I would think so. I tickle both carbs until they barely weep, close the tap, give the bike two kicks with ignition off, then turn ignition on and kick.
 
Fast Eddie said:
What carbs do you have?

You say you cleaned out the jets, but the pilot jets are very difficult to clean on mk1 concentrics, some would say impossible without modification (search Old Brits guides for this).

Carbs also wear: slides, bodies, needles, needle jets all wear.

50 plus year old carbs WILL be worn. They could also have none standard jets / needles.

So, stripping the carbs to verify what slides, needles, spray tubes, jets you have, and what condition they are in, is a needed step.

It’s similar with the ign: wires, black boxes, pick up plates, HT leads, plug caps, etc can all suffer age / use related degradation.

So… when it comes to problem solving on a 50 plus year old bike like this, it is often NOT a case of searching for one finite root cause, it is often a case of several contributory causes (each one quite minor alone) combining to cause your symptoms. Therefore, what is required is to ‘confirm / revert to standard’ with the relevant systems / parts.

You DO have one known issue, the coils. IMO you are pissing in the wind trying to work around this. You need a good spark, so having the correct coils is a real no brainer.

Then, you need to calmly, methodically, go through and rule out all of the potential contributory causes mentioned above and confirm / revert to standard condition, which means repairing or replacing parts that are incorrect, suspect or worn.

If it were me, and I wanted a good starting and good running bike (and some will disagree with this), I’d put a Tri Spark ign and two new Tri Spark coils on it straight away.

Then I’d strip the carbs as mentioned above and make a decision on them. Meaning, if they’re good and just need a clean then I’d use them. If the bodies are worn, or if I had to spend a lot of money on new parts for them, I would bin them and fit new Premiers.

I know you’re trying not to waste money, but I assume you don’t want to waste a lot of time either right, and want a nice starting and running bike? At the end of the day, a new Tri Spark and a pair of Premier carbs really does provide an easy starting, well running machine (provided the rest of it is ok of course). If you’re planning on keeping it and enjoying it for many years, it’s really not a big investment to make on a bike and is a quick way of ruling out dozens of potential issues.

By the way… @SteveBorland is based in Denmark and has (or had) a pair of Premier carbs for sale… they’d be much cheaper to ship than new ones from England I imagine.
Click to expand...
Thanks for this in-depth post.

I have bought the carbs from @SteveBorland. They are with my father-in-law in Denmark and will be picked up in June. The carbs fitted to the bike right now are resleeved. I am usure about the condition of the needle jets.

I will be buying a pair of 6 V coils later today. It seems good investment and they will be correct also if I decide to change the electronic ignition to a Trispark, Panzon or newer Boyer at a later date.

So the plan is then to fit the new coils, check compression, use new fuel and plugs and see if that improves things.
 
I had some carbs re sleeved and bored out to 33.5mm some years ago. Afterwards they gave me really annoying intermittent problems despite blowing them through with compressed air, carb cleaner, etc.

In the end I boiled them in a large saucepan with some detergent !

The crap that came out was amazing, along with a very unpleasant looking piece of swarf.

The swarf was clearly a result of the work I’d had done on them. They were fine after this.
 
Good news, it starts! I got and fitted the new 6V coils last week. This Sunday I finally got the time to adjust the carbs and make a new attempt. After a bit of adjustment the bike now starts after a kick or two.

But the exhaust pulse from the left cylinder is a lot weaker than the right. It also stumbled when I raise the revs.

I am suspecting an air leak or some blockage in the pilot circuit? Or could it be something else? Suggestions and troubleshooting-steps are much appreciated.
 
solbero said:
Good news, it starts! I got and fitted the new 6V coils last week. This Sunday I finally got the time to adjust the carbs and make a new attempt. After a bit of adjustment the bike now starts after a kick or two.

But the exhaust pulse from the left cylinder is a lot weaker than the right. It also stumbled when I raise the revs.

I am suspecting an air leak or some blockage in the pilot circuit? Or could it be something else? Suggestions and troubleshooting-steps are much appreciated.
Click to expand...
Suggested approach already laid out in post 25…
 
Good to hear progress and 6v coils are right direction. Generally, stubling just as throttle opens is a sign of overly lean condition from pilot jet and potentially needle clip position. When cleaning carbs, i do not stop until there is a good spray up out each of the two tiny holes in the carb throat. A spray straw can be used with some finagling to spray down into one of the holes to see spray oit the other...even possible with carbs on bike if the slides are removed.
Confirm needles are on middle clip groove and perhaps try raising the needle (clip to next lower groove) to increase richness of mixture during transition from pilot to needle jets.

I use locktite gasket maker on both sides of the insulator "gasket" on intake manifolds. Check for hairline cracks on manifolds esp around the balancer pipe spigots. Confirn balance pipe hose is tiggt, not cracked.
 
Out of sync slides will also cause on stumble on opening of throttle that clears the more the throttle is opened.

Back to basics and tune the carbs from the beginning including sync first. But first check the valve clearances.
 
I went through the different parts of the carbs one-by-one. Turned out the nuts holding one carb to the manifold was a not finger-tight enough. Tightened them and that took care of the air leak. But the carbs are worn. Looking forward to picking up the new Premieres in June. The old carbs will just have to do until then.
 

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