73 850 was running then it stopped and it wont restart

Hi guys.

So, I started my bike in the garage just because I hadn't ran it in a while so I just want to run it for a few minutes. It took a bout 4-5 kicks since I hadn't started in a while and then it ran fine. I left it running longer than I planned to because I got on the phone but basically it ran for about 10 minutes fine, then it quit... and ever since then it Wong restart.

Ive tried run starts, wont even try to start.


-full tank of new gas
-nice blue spark at both spark plugs
-fully charged battery


Any ideas on why it would quit and stay quit?

Check if the spark plugs are wet with fuel.

Er, taps on?

Crap in the carbs? been stood for a while.

The bike was running,/idling in my garage, so everything was working, then it stopped running and I haven't been able to re start it.


I cant tell if the plugs are wet, they dot seem to be. The carbs were rebuilt a few months ago and its been running fine since, doesn't mean something not wrong wit them but its a little low on my list.

Taps are on, both just in case.
The bike only stood for maybe a month, not sure thats enough to make the fuel go bad. Specially since it ran fine for a good 10 minutes before it quit?

I don't think they care to idle that long,,, tend to load up. But, you say there is a nice fat spark, now? Unless you really need to get it going right now, I'd keep the plug out and let the cylinders dry out. Put the plugs back in tomorrow and give it a whorl.

All is well. You are at home in the garage. Plenty of time and low effort to do the entire trouble shooting routine.

Empty each carb into a clean container to check for water and debris. Turn on tap and check again to see if
you flushed anything out and to make sure the lines are indeed feeding. If in doubt pull the petcock and check screens.
As you likely have no problem, time to check plugs. What do they look like? Do you indeed have spark itself?

Well have at it, fuel, vacuum, spark, compression. The usual suspects.

Id be sort of unwilling to just let the bike idle for any length of time anyway.

The spark plugs may have sooted up or fouled from idling so long.
Even though they may not not look all that bad.

Try it with a new set of plugs in there.

If you have a spark now, and it kicks over with compression, I would look at the fuel system.

If the carbs flood with tickling, then fuel starvation is probably not the problem. If they don't flood, then starvation may well be the problem

Take the fuel bowls off - you can do that with the carbs on the bike - just take the fuel line off the bowl and remove the two screws that hold each bowl to the body.

You can check the nylon filters in the banjos, and clean out any junk that may have accumulated. You can check to see if there's water in the fuel, too, if you remove the bowls carefully, or drain them into a container. The water will separate from the gas and sit in a puddle under the fuel. Too much water in the gas will keep the bike from running.
I've seen the main jet come out with the fuel bowl - vibrations from the engine caused it to unscrew from the body, and drop into the bowl. generally, the bike won't start when this happens.

If everything else is good, then check to see if the pilot circuit is plugged. A strand of wire from an old cable makes a good snake.

Did you have the choke on when idling? Is it on now? No reason to ever leave a norton idling any longer than to put jacket, helmet, and gloves on.

Maybe your advance mechanism came loose, and the timing is way out ??? Not unheard of, the Commando doesn't have a locating peg on the cam for the advance assembly. It is just a taper fit, they should have copied Triumph IMO. :mrgreen: Cheers.

Biscuit said:

I don't think they care to idle that long,,, tend to load up. But, you say there is a nice fat spark, now? Unless you really need to get it going right now, I'd keep the plug out and let the cylinders dry out. Put the plugs back in tomorrow and give it a whorl.

Click to expand...

Interesting ... this makes the most sense so far, thank you.

Onder said:

All is well. You are at home in the garage. Plenty of time and low effort to do the entire trouble shooting routine.

Empty each carb into a clean container to check for water and debris. Turn on tap and check again to see if
you flushed anything out and to make sure the lines are indeed feeding. If in doubt pull the petcock and check screens.
As you likely have no problem, time to check plugs. What do they look like? Do you indeed have spark itself?

Well have at it, fuel, vacuum, spark, compression. The usual suspects.

Id be sort of unwilling to just let the bike idle for any length of time anyway.

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So far the theme is I might've let the bike idle too long.. never thought about that since I never et it do that until this time.

BillT said:

If you have a spark now, and it kicks over with compression, I would look at the fuel system.

If the carbs flood with tickling, then fuel starvation is probably not the problem. If they don't flood, then starvation may well be the problem

Take the fuel bowls off - you can do that with the carbs on the bike - just take the fuel line off the bowl and remove the two screws that hold each bowl to the body.

You can check the nylon filters in the banjos, and clean out any junk that may have accumulated. You can check to see if there's water in the fuel, too, if you remove the bowls carefully, or drain them into a container. The water will separate from the gas and sit in a puddle under the fuel. Too much water in the gas will keep the bike from running.
I've seen the main jet come out with the fuel bowl - vibrations from the engine caused it to unscrew from the body, and drop into the bowl. generally, the bike won't start when this happens.

If everything else is good, then check to see if the pilot circuit is plugged. A strand of wire from an old cable makes a good snake.

Click to expand...

The carb flood fine and fast, that s wy I havebt suspected rule starvation yet. Its starting to look like a spark plug issue even tough the bike has sat in the f-=garage 1-2 days between attempts. Ill try pulling plugs and even putting in new ones. I have spark and carbs flood but it wont get gong with a running start so thats whats baffling me. Even if the sparks were fouled you'd thing it would at least TRY to start with a goo doling downhill running start no? It doesn't even attempt to.

michael levato said:

Did you have the choke on when idling? Is it on now? No reason to ever leave a norton idling any longer than to put jacket, helmet, and gloves on.

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no choke on this guy, got yanked by previous owner

nortriubuell said:

Maybe your advance mechanism came loose, and the timing is way out ??? Not unheard of, the Commando doesn't have a locating peg on the cam for the advance assembly. It is just a taper fit, they should have copied Triumph IMO. :mrgreen: Cheers.

Click to expand...

Aw man, hope its not that deep, but not completely crazy now that I think about it leaving it idling that long and how it backfires every 10-15 kicks or so

While I've never had this exact situation, I have had a few occasions of the bike refusing to start after being laid up for a while.
Agree with BillT - What's worked for me also is to remove the pilot screws (after noting the 'turns-out' setting) and clear the pilot jet with a piece of fine wire.
I use the brass wire mesh from wine bottles, but the effect is the same.
Easiest/cheapest thing to try at any rate
Previous suggestions also sound good, and I'd also favour a new set of plugs and a quick check that the timing hasn't suddenly adjusted itself.
I've encountered Electronic Ignition stators appearing to be tight in the cam but actually free enough to spin slightly due to the supplied retaining bolt being a little overlong and bottoming out.
Something I now check on every build... :roll:
Is yours still on points, or electronics?

I sometimes let my bikes idle for a while, and yes they get a bit hot, but I can't see it doing any lasting harm. Just not the best time to set the pilot screws.

Hope you get it nailed

Are you running points ignition or electronic?

Check the simple stuff:

-is the kill switch sticking or corroded?

-look for a grounded wire inside the headlight shell or a skinned wire on the harness

-old, crappy ignition switch with corroded contacts.

-add a few temporary direct hot wire to the ignition box, and temporary ground wires to the ignition circuit and engine to eliminate electrical causes.

-old battery with a single bad cell or a weak cell. check the water level on your battery, leave the headlight on for 5 minutes and check voltage

-remove the air filter and visually inspect (with a dental mirror if need be) your slides going up and down when you twist the throttle. Perhaps a cable let go...

-Reach a finger into the mouth of each carb and gently feel if the needle is moving up and down with the slide body when you twist the throttle. The needle clip could be dislocated and the needle is now sitting in the jet... (the bleeders will work, but the bike probably won't run)

-check all the intake manifold bolts for tightness and inspect the manifold for cracks

... a little deeper:

check compression

-check valve train for proper clearances

Drsus-

Brother, I have 40 years with Brit bikes and I started with a TRident which we all know is a lot more funky than a Commando and I have NEVER heard of idling too long as being an issue and I live in the southern US where its as hot as the devil's balls right now

- Always remember that the Commando is an extremely simple motorcycle and that any issue is ALWAYS the simplest root cause. Again - simplest root cause

There are only 3 things involved in a relatively healthy motor starting and running - Fuel, Spark, and timing. That's it, nothing else.

Fuel -
- You mentioned that the float bowls flood as normal, So, it is not the tank vent. If it starts, runs for a short period of time and dies, check the vent. Next, drop the float bowls. You can do that without removing the carbs. Inspect them for something obvious like a lot of trash and clean them with carb cleaner. Next, pull the jets. Again, you can do this with the carbs still in place. Check them carefully and make sure they are not blocked. While the jets are out, look at the bottom of the exposed needles and make sure one is not obviously lower that the other. If the jets are clear and you don't find anything obvious, put them back together. Your problem is not fuel. I caution you not to over think carburetors. Amals are really simple and really reliable and they don't fail catastrophically, they just get sloppier and sloppier as they wear out. I chased gremlins in the 3 trident carbs for years and years till on a visit with Les Williams in England he explained how they work and helped me recognize that my issues were all in the ignition.

Spark - OK, if all of the above went well and you have ruled out fuel delivery; lets check the spark. First - put the key in the ignition and turn the bike on and check that you have lights and horn. If these systems are not working, you have a short circuit and it should be obvious because the bike was running. start looking for a lose wire or something melted. Assuming that this checks out and you don't have a general short or electrical failure , pull one of the plugs. Clean and gap it and hook it back up to the spark plug lead. Lay it on the side of the motor and with your garage relatively dark, kick the bike over and check to see if you have a spark. If you have spark , the problem is timing which we will talk about below. If not, go to the kill switch on the handle bars and clean the contacts and check again for spark. If you now have spark, you are good to go. If not, the problem is in the ignition system. If you have electronic ignition, check the box. (When you are under the seat be careful. My MK3 has a capacitor that will light you up if you are not careful).

Timing - If you determined that your fuel delivery system is normal. And you had spark at the plugs and it still won't start - the only thing left is timing. Static time the bike and make sure the advance unit moves freely.

Once you've been through this model the bike should start. You should be able to do all of this in a couple of hours. I'm not saying that your problem isn't some bizarre multifaceted cascading multi-system bla bla bla one in a million event - Well, yes that's exactly what I'm saying

Let us know how it goes
Cheers,
Cameron

Commando Cam said:

Drsus-
There are only 3 things involved in a relatively healthy motor starting and running - Fuel, Spark, and timing. That's it, nothing else.
Cheers,
Cameron

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What about compression?