Navigation

You are here: Home / Messages / Commando / Intermittent fault

Intermittent fault

Up to Commando

Intermittent fault

Posted by keith_smith2 at October 25. 2018

I have a 1972‭ ‬interstate commando that has developed an intermittent fault‭. ‬It usually becomes evident after I have ridden for 40+‭ ‬miles‭, ‬it starts to what I would term as feeling like a miss-fire by starting to get jerky‭, ‬some times it will get through this and then be fine for a while and in the worst case completely cut out‭.

‬On my last ride it completely cut out and would not restart‭, ‬I took out the plugs they were fine‭, ‬fuel was getting to the carbs‭, (‬they are a new pair of amals just 3‭ ‬months ago‭), ‬I took off the ignition cover to check the wiring of the pazon ignition system and all looked OK‭, ‬and checked that all other wiring‭ ‬was connected‭. ‬After about half an hour of various attempts to kick it over it started and I rode the 20‭ ‬miles home with out further issue‭.‬

Any advice will be greatly appreciated‭.‬

Re: Intermittent fault

Posted by ian_soady at October 25. 2018

This is possibly misleading but when I had a very similar problem with my Commando it was an intermittent connection between the Boyer pickups and the control box - the Boyer used silly crimp on connectors and these were dismantling themselves internally. As I say, different system but maybe worth a check? One problem with the Commando is that although the rider doesn't feel any vibration the engine is still suffering it - in fact more than with a Domi or similar as the frame isn't damping it.

Re: Intermittent fault

Posted by peter_austin at October 25. 2018

Previously keith_smith2 wrote:

I have a 1972‭ ‬interstate commando that has developed an intermittent fault‭. ‬It usually becomes evident after I have ridden for 40+‭ ‬miles‭, ‬it starts to what I would term as feeling like a miss-fire by starting to get jerky‭, ‬some times it will get through this and then be fine for a while and in the worst case completely cut out‭.

‬On my last ride it completely cut out and would not restart‭, ‬I took out the plugs they were fine‭, ‬fuel was getting to the carbs‭, (‬they are a new pair of amals just 3‭ ‬months ago‭), ‬I took off the ignition cover to check the wiring of the pazon ignition system and all looked OK‭, ‬and checked that all other wiring‭ ‬was connected‭. ‬After about half an hour of various attempts to kick it over it started and I rode the 20‭ ‬miles home with out further issue‭.‬

Any advice will be greatly appreciated‭.‬

Re: Intermittent fault

Posted by peter_austin at October 25. 2018

Hi Keith,

I had a very similar mystery misfire that took nearly 6 moths to trace as it only occurred on the road after 30 miles or so. I had checked all the usual things and the bike would run perfectly on the stand, so very difficult to trace/test. In the end it turned out to be a dodgy HT lead and as soon as I replaced these the fault disappeared. I hope this helps.

Regards,

Pete Austin

Re: Intermittent fault

Posted by jonathan_newton at October 25. 2018

Previously keith_smith2 wrote:

I have a 1972‭ ‬interstate commando that has developed an intermittent fault‭. ‬It usually becomes evident after I have ridden for 40+‭ ‬miles‭, ‬it starts to what I would term as feeling like a miss-fire by starting to get jerky‭, ‬some times it will get through this and then be fine for a while and in the worst case completely cut out‭.

‬On my last ride it completely cut out and would not restart‭, ‬I took out the plugs they were fine‭, ‬fuel was getting to the carbs‭, (‬they are a new pair of amals just 3‭ ‬months ago‭), ‬I took off the ignition cover to check the wiring of the pazon ignition system and all looked OK‭, ‬and checked that all other wiring‭ ‬was connected‭. ‬After about half an hour of various attempts to kick it over it started and I rode the 20‭ ‬miles home with out further issue‭.‬

Any advice will be greatly appreciated‭.‬

For me two areas to focus on, heat and mixture.  40 + miles would suggest  everything is up to temperature, then the  problem emerges.  Coil failure/fault is commonly coincidental with heat. Mixture can also be an issue as your engine  temperture rises or airation of the fuel due to prolonged vibration,  make sure you are not on the too lean side of the settings especialy when it is hot.  How does it start  once you have the problem?  it may be an indicator of either of the above.  As Ian said electrical connections should be inspected/ remade if in doubt.  I would suggest riding it  differently to see if you can induce the falut at a different stage.  Load it up heavily, run it on a light throttle, over rev,  under rev, try to get it it play up at a differnt point and then eliminate potential causes .  I did have a fuel hose  delaminate internally and restrict the flow once; that only showed up when riding "enthusiasticaly".

Interesting problem  keep us posted on what you try ... 

 

J

Re: Intermittent fault

Posted by andrew_heathwood at October 25. 2018

Keith

I had a very similar problem on my 1972 Roadster.

I found this a difficult fault to repeat.  I reckoned it was heat and electrically related since the spark plugs were not sparking when the problem occurred although they returned the next day.

I did the following:

i) Ensured that the ignition module was not too well 'tucked away' from any airflow.

ii) Made a better earth connection from one of the coils - this connection is shared with the Pazon ignition module - using a crimped eyelet connector bolted to a bare frame point.  Pazon instructions emphasize the need for good earthing.

iii) Ensured there was a good clean earth point from one of the bolts securing the top engine plate (fits to the head steady) and wired a connection to a frame earth point. This ensures that the engine has a good earth connection by-passing the isolastics.  Mentions of engine earth wires are a bit 'buried' in the workshop manual (Pt No 065146). See:

Section C37 (para 7)

Detach engine ground wire attached to lower left crankcase stud.

Section F4 (para 15)

Fit the main head steady plate to the cylinder head, securing with three socket headed screws. Note that the centre screw secures the ground (earth) tab on the red leads.

 

I don't know which of the 3 changes solved the problem but it has never recurred.

Andy

Re: Intermittent fault

Posted by graham_powis at October 25. 2018

Is the problem apparent throughout the rev range? If the problem manifests itself lower down in the rev range could the pilot jet circuit be a fault. Unlike the Monobloc the Concentric has the pilot machined into the casting, Many years ago I dropped my concentric on the floor, thinking no more about it I reaffixed it. The bike wouldn't run at low revs, once the power was opened up it was O.K and then lumpy as soon as the revs dropped. By dropping the carb I had distorted the carb body and distorted the pilot circuit, the problem dissapeared once a new body was fitted. I suppose a niggling fault like this is best dealt with by many brains, someone on the forum will be right?

Good Luck,

graham

Re: Intermittent fault

Posted by keith_smith2 at October 25. 2018

Thanks for the responses so far, I must admit I think it is more electrical than carb related.

I did fit new HT leads just over a year ago, not because the existing were giving problems just wanted to fit new ones, I will fit the old ones back and see how that goes.

How can I tell if the coils are failing.

I will also be checking all the electrical / earth connections.

In response to Graham Powis's question the fault happens through the and the plugs are a good colour

Shame the weather is getting colder as it makes it harder to go for the longer runs to test out.

As a bit of background this is my first classic bike, so its very much a learning curve for me even though I have had it for 4 years now.

Thanks

Keith

Re: Intermittent fault

Posted by keith_smith2 at October 25. 2018

Sorry the post lost some of my answer:

The sentance: In Response should have been:

In response to Graham Powis's question the fault happens throughout the rev range at normal speeds and revs. I fitted the new Amal's because I could not get it to tick over evenly and was a bugger to start when not used for a few weeks (sometimes over 20 kicks), now it ticks over evenly and starts 1st-2nd kick most times, the and the plugs are a good colour

Re: Intermittent fault

Posted by mike_hadden at October 25. 2018

Previously keith_smith2 wrote:

I have a 1972‭ ‬interstate commando that has developed an intermittent fault‭. ‬It usually becomes evident after I have ridden for 40+‭ ‬miles‭, ‬it starts to what I would term as feeling like a miss-fire by starting to get jerky‭, ‬some times it will get through this and then be fine for a while and in the worst case completely cut out‭.

‬On my last ride it completely cut out and would not restart‭, ‬I took out the plugs they were fine‭, ‬fuel was getting to the carbs‭, (‬they are a new pair of amals just 3‭ ‬months ago‭), ‬I took off the ignition cover to check the wiring of the pazon ignition system and all looked OK‭, ‬and checked that all other wiring‭ ‬was connected‭. ‬After about half an hour of various attempts to kick it over it started and I rode the 20‭ ‬miles home with out further issue‭.‬

Any advice will be greatly appreciated‭.‬

Had a similar problem ,turned out to be a loose battery connection.

Re: Intermittent fault

Posted by graham_powis at October 25. 2018

Previously keith_smith2 wrote:

Thanks for the responses so far, I must admit I think it is more electrical than carb related.

I did fit new HT leads just over a year ago, not because the existing were giving problems just wanted to fit new ones, I will fit the old ones back and see how that goes.

How can I tell if the coils are failing.

I will also be checking all the electrical / earth connections.

In response to Graham Powis's question the fault happens through the and the plugs are a good colour

Shame the weather is getting colder as it makes it harder to go for the longer runs to test out.

As a bit of background this is my first classic bike, so its very much a learning curve for me even though I have had it for 4 years now.

Thanks

Keith

Remember you don't need ballast resistors with the Pazon {just a thought}

Re: Intermittent fault

Posted by lance_crossley at October 26. 2018

Previously keith_smith2 wrote:

I have a 1972‭ ‬interstate commando that has developed an intermittent fault‭. ‬It usually becomes evident after I have ridden for 40+‭ ‬miles‭, ‬it starts to what I would term as feeling like a miss-fire by starting to get jerky‭, ‬some times it will get through this and then be fine for a while and in the worst case completely cut out‭.

‬On my last ride it completely cut out and would not restart‭, ‬I took out the plugs they were fine‭, ‬fuel was getting to the carbs‭, (‬they are a new pair of amals just 3‭ ‬months ago‭), ‬I took off the ignition cover to check the wiring of the pazon ignition system and all looked OK‭, ‬and checked that all other wiring‭ ‬was connected‭. ‬After about half an hour of various attempts to kick it over it started and I rode the 20‭ ‬miles home with out further issue‭.‬

Any advice will be greatly appreciated‭.‬

Hi, Keith.

In my experience whenever you have multiple possible causes of a problem it's always the last one you attend to which is the culprit!

I had similar running symptoms to you with my 650SS following recently refitting twin Concentrics, though I didn't have the restarting problem. It turned out to be fuel starvation to one cylinder caused by the float needle not being lifted from its seat all the time by the lowering float, probably caused by my having tweaked the stay up float bracket in the past whilst adjusting the fuel level and exacerbated by the needle being a brass, viton tipped one and thus a bit heavy for the fuel pressure to lift. Shouldn't be your problem since you state your carbs are new but I've had issues with Amal quality control in the past so it might be worth checking if all else fails. Solved my problem by refitting an older plastic float for the time being. To add to the problem the idle circuit in that carb wasn't quite clear either and needed a good clear out, which sorted the idling. Back to how it should be now.

Good luck.

Re: Intermittent fault

Posted by alan_sessions at October 27. 2018

Had a similar problem with my 850 mk3 with twin Amals - over 6 months, ran dedicated earth lead & power feed to the EI, missing out the handlebar circuits - swapped everything electrical except the wiring between the EI black box & points housing - when I eventually stripped this out, there was a small nick in the cable where it went through the heady steady. After 30 miles, there is a lot of engine heat (plus vibration) that rises up under the tank & may affect wiring & black box if mounted there (my black box is behind offside side panel)

Re: Intermittent fault

Posted by christopher_winsby at October 27. 2018

Hot wire ignition via a fuse and switch so that it runs on sa nerw wiring circuit. Look up Bushmans Amal they have a simple mod so that you can get to both sides of the pilot jet (unlerss you have the new premiers) bush. The clean out carbs and go from there. You say they were new carbs, from where? Quality of new parts can be suspect with reports of swaf contamination, badly fitting welch plugs etc. Spark plugs are another thing to watch out for, getting cheap  spark plugs can be false economy.

I have had carb issues, intermittent Boyer black box and poor quality connectors.

Re: Intermittent fault

Posted by eelko_byker at October 27. 2018

I had a simular problem my bike would quit intermitantly a year later it would  quit after 10 min of running and restart after a half hour cool down I removed the pazon and put my old boyer back problem solved I sent the pazon back it was tested and found to be defective they sent me a new unit no more problams

Re: Intermittent fault

Posted by andrew_heathwood at October 27. 2018

Previously keith_smith2 wrote:

Thanks for the responses so far, I must admit I think it is more electrical than carb related.

I did fit new HT leads just over a year ago, not because the existing were giving problems just wanted to fit new ones, I will fit the old ones back and see how that goes.

How can I tell if the coils are failing.

I will also be checking all the electrical / earth connections.

In response to Graham Powis's question the fault happens through the and the plugs are a good colour

Shame the weather is getting colder as it makes it harder to go for the longer runs to test out.

As a bit of background this is my first classic bike, so its very much a learning curve for me even though I have had it for 4 years now.

Thanks

Keith

 

Keith
Do the plugs still spark immediately after the fault occurs? I.e. with both plugs removed and earthed against the cylinder head, ignition on and the engine kicked over.

If you have access to a multimeter, one test to complete on coils - once disconnected - is measuring the primary resistance (across the + & - terminals) and secondary resistance (between either + or - and the output terminal). Expected values I've seen are 1.7 to 2 ohms primary and approx 5100 ohms secondary. I'm not sure how useful this will be with an intermittent fault and this is really a test for a failed coil to be done back in your garage and not on the road.

I do have some good spare coils which you are welcome to borrow for the cost of the postage. Message me if you want me to send them.

Good to see your checking those earth connections. I made sure the earth connections to frame and engine parts used eyelet (ring) terminals where possible. This is preferable to the Lucar spade type connections for this use.

If you decide to buy new coils instead I can recommend the PVL ones.

Andy

Re: Intermittent fault

Posted by boo_cock at October 27. 2018

I had a similar problem with my T100 Daytona recently. I fitted the twin carb head replacing the single carb head, Without thinking about it I did not fit the heat insulation spacers on the inlet manifolds. As a result, the carbs got hotter than hell in 30 or 40 miles. Then it would miss fire at low revs. If I stopped, then it would not start until it had cooled down. Fitted heat spacers and now all is well again. Laughing

Re: Intermittent fault

Posted by keith_smith2 at October 29. 2018

Thanks for all the replys‭.‬

 

On Sunday I went through most of the wiring and found the earth/pazon shared connection on the coil pulled out with no resistance so have now fitted a new soldered on connector and also checked/cleaned the various earthing connections‭. ‬Until I get a chance‭ ‬to give it a good run‭, ‬hopefully next weekend I don’t know if that was the issue‭.‬

 

The Amal concentrics I fitted were the premium versions and I did fit the heat insulator spacers‭. ‬

Keith

Re: Intermittent fault

Posted by christopher_winsby at October 29. 2018

Previously keith_smith2 wrote:

Thanks for all the replys‭.‬

 

On Sunday I went through most of the wiring and found the earth/pazon shared connection on the coil pulled out with no resistance so have now fitted a new soldered on connector and also checked/cleaned the various earthing connections‭. ‬Until I get a chance‭ ‬to give it a good run‭, ‬hopefully next weekend I don’t know if that was the issue‭.‬

 

The Amal concentrics I fitted were the premium versions and I did fit the heat insulator spacers‭. ‬

Keith

Having had problems I now crimp and solder all connections then shrink sleeve to the insulation to bridge the solder/wire joint.

Re: Intermittent fault

Posted by david_broadbent at November 20. 2018

I had a similar problem on my Commando which would start running rough after 10 miles or so before finally cutting out . Once it cooled off it would start up again as though nothing had happened. I finally traced it to the wire to the points plate which had fatigued and parted within its insulation. When it was cold the wire insulation kept the ends close enough together but failed when the wire got hotter. The answer was to use a very much higher grade of wire which has many individual filaments to it, as used in the aerospace industry. The many finer wires are far more resistant to fatigue breaking. The wire had actually parted between the engine and the frame which is where all of the motion between those points creates the fatigue failure.

That was about 15 years ago and the problem has never returned.

Re: Intermittent fault

Posted by ian_soady at November 21. 2018

The Commando is particularly prone to this type of problem as the engine is moving significantly with respect to the frame therefore the wires are being constantly flexed.

Re: Intermittent fault

Posted by philip_rattray at November 21. 2018

A friend had the same problem ,turns out it was the fuel tank not venting.

worth a look

Powered by Ploneboard
This is Brio Diazo Plone Theme