John's 72 Commando woes

I am going to throw my two cents in and go with a dodgy coil or flaky EI. I have seen both fail and heat brings the failure out. The fact that the bike can sit and then start makes me think coils.

batrider said:

Choke left on?

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John Rollins said:

Choke is off. Thank you for your input, it is appreciated.

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cliffa said:

Welcome John. You have Norton in your blood, so no wonder you've been hankering after one. Your grandad was a regular name on race programs in the 60's 70's and 80's, and I remember it well. According to this article on GusKhun.net he narrowly missed out being in the JPN team after he and Peter Williams won the Thruxton 500 mile endurance race in 1970 on a Commando.

Charlie Sanby

www.guskuhn.net

This is a great picture of him jumping Ballaugh Bridge on the IOM, this time Guzzi mounted..


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A thought about your bike issue. Contrary to most other carbs the choke will be off when the when the choke lever is all the way counter clockwise ( i.e. cable under tension) so it may be that the choke cable for the right carb has snapped and allowed the choke plunger to drop.

Also check that the plug lead is fully pushed into the coil. I found mine was not, and was being held in place by the boot so the spark was having to jump 1/2" before it ever got to the plug.

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John,
Boggin underway is classic choke issue. The Choke is counterintuitive.
Needs to be pulled tight, the lever runs across the handlebars, not in line.

After that, loose coil wire. They come loose with the engine jumping around.

After that, carb clean up. These classics with carbs are at the mercy of modern gas.
Gas evaporates leaving deposits, pretty much making life miserable for us classics.
Learn to run the engine dry with taps off before storing, or better yet, drain the carbs.

GREAT FAMILY PROVENANCE!!!
Welcome aboard............

First thought is it sounds like a lack of fuel.
My check list would be…
1. Check fuel cap filler cap is breathing ok. Check the pinhole is clear. Try opening the fuel cap when the bike bogs.
2. check the fuel flow from the petcocks. Does running with both petcocks open make a difference?
3. check carb float heights.
Whatever you do, only make one change at a time!

nopdog said:

If the bike has inline fuel filters they can become full of gunk and restrict the fuel flow hence it bogs down under load. Same with the fuel tank petcocks, over time they gunk up and will restrict the fuel flow.

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Yes, old fuel that has been sitting a while can cause havoc. If it's been sitting, the carbs are probably fouled. Probably best not to guess and go ahead and pull the carbs and thoroughly clean all the pin hole orifices (with small needle like carb cleaners). This is a good opportunity to check your bowl floats (do they float and if they do, what's the cutoff level) and float valve, as well as what jets you have.

If they are clean and set up the same and are getting fuel with functional floats and still not running the same on both sides, it's probably something else.

Hi John, The Norton club. You will get to meet other owners , not just on the net. Its a totally different scene in the UK. More about using the bikes and not so much about heavy duty modification. I regularly meet up with 30 or more club members, and can ride out with members every other week if the weather permits. Gus Kuhn bikes are owned by members.

Welcome to the fun! I’ve had every problem known to man on my 72 in the last year. I was also fouling plugs and ran through the carbs at least 4 times. Replaced everything internal to the carbs and I think the NGK plugs were part of the issue. I put some autolites in while waiting for champions and it seems to be running well. Make sure you check all of you setting before dismantling them. Idle air setting, jet size and needle position. I’m doing some more test rides this weekend to decide if I need to drop the needles a setting.

Points won’t be too sensitive to battery voltage but in my experience electronic ignitions are. Given you symptoms it may be stator output vs battery though.

Congratulations and good luck! Not too many shortcuts here but you’re gonna learn a lot!

Hi John
We (crmc) still race for the Charlie Sanby trophy. One of our King of (circuit) events.
Charlie's was always linked to the Lord of Lydden trophy. Big man a gentle giant & a fast rider.
We've not been to Lydden for a while & Charlies race has moved around other circuits. He raced with the Crmc & I believe he rode his last race at Lydden while he was very I'll. I will try & find the write up the club did. Allan Robinson the voice from the tower gave him a beautiful eulogy.

Chris said:

Hi John
We (crmc) still race for the Charlie Sanby trophy. One of our King of (circuit) events.
Charlie's was always linked to the Lord of Lydden trophy. Big man a gentle giant & a fast rider.
We've not been to Lydden for a while & Charlies race has moved around other circuits. He raced with the Crmc & I believe he rode his last race at Lydden while he was very I'll. I will try & find the write up the club did. Alan Robinson the voice from the tower gave him a beautiful eulogy.

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Charlies last race was at Pembrey, he passed away a few days later

He was given special permission to start from the back as he needed Wally to push him for the start

Is the petrol tank fiberglass? These are notorious for dissolving in modern ethanol fuel, leading to gumming up of the carbs.

Also when you say problem happens under load, what exactly do you mean? Riding along at steady speed, going up a hill, or just anytime you give it some beans? Make some tape marks on your throttle grip and watch how far its twisted when the issue occurs. This will tell you what carb jet or jets are involved. First 1/8th turn is idle circuit. 1/8-3/4 turn is needle. After 3/4 turn is beginning of main jet.

Check out the excellent Bushman's Guide to Amal concentric carbs, link found under the Technical Information thread of this forum.

Yeah, it's 50 years old now and that's 50 years that you don't know about it's history. I've owned one since '71 and had some of these issues and it's usually carbs if it's just one cylinder. A black spark plug indicates a too rich mixture or poor spark. You'll have to verify that the choke slider is actually functional visually by removing the air filter and seeing that the slider does move upward when it should be off choke. It is cable operated and you can check that both carbs act the same when cycling the choke lever.
You can always swap coils and plug wires, but it always came back to carbs for any of my problems.
I think the most essential skill for maintaining my Commandos was setting up the carbs to be synced and checking all the other settings like needle clip positions, cleaning out idle mixture passageway with a guitar G string and checking for wear in slides. You should also inventory the carbs to see if both carbs match components, but that probably isn't the root cause here, just good to know that they do match.
Again, you're running too rich on one cylinder and that indicates more fuel that air.

Hi John, welcome to the wonderful(ly) world of Commandos! FWIW also check the affected side’s main jet hasn’t come loose . Had that and it does mess things up as you’ve described. good luck

SteveC said:

First thought is it sounds like a lack of fuel.
My check list would be…
1. Check fuel cap filler cap is breathing ok. Check the pinhole is clear. Try opening the fuel cap when the bike bogs.
2. check the fuel flow from the petcocks. Does running with both petcocks open make a difference?
3. check carb float heights.
Whatever you do, only make one change at a time!

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That's where I'd start, because they're simple checks, before getting into ignition. Could be as simple as rust blocking the peacock filters, reducing flow.

Sounds like dodgy coils .

Theres a CYCLE Magazine link here somewhere " Great Coil test " showing how useles Lucas coils are . After a decade a Lucas Car Coil is usually trash .
The SPORTS Coil was better . A 1/2 in plus rathern 3/8 weak spark .





The Ring Ding 350 ( they pretended it was ' Race Developed " but we know better ! )

THAT SAID , Id wire the COILS DIRECT , ish . cut out the drivle . IF its still dodgy , its cause the coils are past their use by date .

Leaving Ign. on can roast em . The shellac insulation can go to the dogs . And other things .

CYCLE found K - Mart coils best , and least expensive . for the Dew Cati superbike . Spraying swithgear full of C.R.C. can help .
Not to Metion the IGNITION SWITCH .

Dismanteled theyre usually oxidised & grubby , No Wonder theye dont work proper ! .



If you have one of these ,
see if you can find a large
sledge hammer & anvil .

The THING being HOT the coil can cease , & re un cease when cooled .

Wire from battery to coil , with a taped accessable ' emergancy dis- connect ' ( pull apart )
twisted join . for ascertaining its NOT a loose wire / connector .

ANY unfirm unclean spade or bullet connectors can be erratic , intermitant , and unsatisfactory .
Custom Adj. FIRM , ALL .

If you can’t fix it with a hammer, it’s an electrical problem

I been watching this thread and your problem, one thing you say you been idling the bike a lot while working on it or what, the ALT won't charge the battery when idling and idling to longocould have a affect to the spark plplugs.

lots of things could be the cause of your problem But you got to go through things one at a time to find the problem, first of all I be tearing down the cards and replace new needles and jets (a carb rebuild kit needed) soak the all the carbs bits ( I soak mine in vinegar work well) make sure the floats are filling up with fluids, if they have petrol in them when you pull them down replace them, after cleaning the carbs make sure all passages have no blockages, refit carbs and see if that was the problem, if no then I be going through the electrics, starting with coils and leads, also new spark plugs, then EI be the next thing to check, also do a load test on your battery as even new batteries can fail, coils can work good when first fired up but as the get warm or very hot could fail,go through the plug leads, replace if nesasry and if still problem go through wiring as old wiring can be brittle from age and cold and hot weather and of course replace any old connections that are showing age, moisture is the biggest killer of electrical connections.

Remember your bike is over 50 years old and not knowing the history of the bike, where it's been parked up or stored can cause problems as you found out one day running fine the next day it's having problems, just be patient and go through things one at a time, and if you get frustrated just walk away and think about don't get angry, find someone close who knows how to do thing, never be afraid to ask as you have been doing here, but I be starting to pull those carbs down first, you never know could be just something simple to fix and looking right at you and make sure the needle clip is seating right under the spring in the slide, and make sure the choke is right, myself removed my chokes over 40 years ago as I got sick of people fooling around with the lever when parked anywhere, been caught out with that one a few times.

Anyway take your time and just work your way through things, you get there and sort it out and you get to know your bike as well, good luck.

Ashley

TBW said:

Hi John, welcome to the wonderful(ly) world of Commandos! FWIW also check the affected side’s main jet hasn’t come loose . Had that and it does mess things up as you’ve described. good luck

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Absolutely . I got stuck in Northern Ontario bush with wife and camping gear on the bike when the left jet assembly dropped out to the bottom of the float bowl . Knew what the problem was with a black carboned - up plug and eventual failure of the plug . Kept swapping the plugs over to keep the motor running until getting to some real help . Terrible gas mileage , where the Interstate tank helped . The jet assembly must be really tight . The carbs are violently shaken like say popcorn .