Hi, New to Norton Ownership, with a Problem!

Hi, I've been using the forum to help me, before taking the plunge and getting my 1975 MkIII Commando roadster 2 weeks ago. I've just registered, to see if anyone can help me with a problem, please.

When I bought the bike it started easily on electric and kick start and settled to idle. A short ride it was smooth and tight, I was smitten! I had it delivered home. It is running a single Amal 34, mk2, with a K&N filter, Boyer ignition and powerbox. As it was very low on fuel, I rode to the garage, 4 miles. It was hesitant on the ride, but got there OK. I put in 1.5 gallons, not to the brim, and rode.

It was still hesitating on a steady throttle, around 40-50mph. I stopped to turn round and it stalled. It restarted and I headed home and it seemed to clear. The bike has only done 3,000 miles since 2013, so I thought it may just be down to that. So I rode on, in the end doing about 50 very pleasant miles, including a stop for a drink, where it ran, idling happily, and restarted with no choke, without issues. 5 miles from home, it stalled at a junction. It then hesitated the rest of the way home and stalled as I pulled in. From that point it only starts on the choke and dies when I switch the choke off.

I've taken the tank off, flushed and dried it out, it was pretty mucky, even some insect bodies in there. I checked the taps and filters, which were clean. They empty the tank with a steady stream, not a gush, but looked healthy.

Removed and cleaned the carb, including .015" guitar string through the pilot hole. Carb cleaner was spraying healthily out the other side of the system. Generally, the carb and filter wasn't noticeably dirty. I very lightly trued the top of the float bowl (oil on wet & dry paper on a flat marble worktop). It didn't need much. I ordered and fitted the maintenance kit from Burlen. I tested float height, it looked a little low, so increased it slightly. It's about 4mm from the brim. Replaced the fuel connector banjo filter, new gasket and put back together. I checked the rubber connector (carb to motor inlet). Looks fine. Cleaned and re-oiled the K&N. Tightened it all up, all fuel tight and tried again. No change. Won't run at all without the choke, even if I give it some throttle.

Battery is on a tender and seems to take a charge fine and a healthy burst with the starter. Theres a spark at both plugs, but they are sooty. Cleaned and gapped, they were about right anyway. Not sure if the snootiness is from running (few seconds at a time) on the choke.

So, I'm out of ideas and deeply frustrated. In the mid point of my ride, it was absolutely fantastic. It's my first 'classic' bike and I'm amazed how well it performs and handles. At least that ride will sustain me while I sort this problem out. I'm thinking there must be something wrong with the carb. The air supply in the pilot system, as it runs on the choke? On the choke, it is at 3,000 revs and rising. The original settings on the carb were pilot air screw almost fully out, which must be wrong, so I went from a 20 to a 15 jet, as recommended in Amal's tuning tips. But, not being able to idle at all, I don't know where to start with the throttle screw or pilot air screw, to then work from.

Sorry my 1st post is long and needy! Suggestions and any potential solutions gratefully received. Many Thanks,

Mart

Screw right out , 15 pilot jet, points to the obvious, it's too small. Try a 25, screw it 1 half turns out, (set it to what your engine needs)

Check your private messages aka Converstations. Look for the envelop at the top/right of the page.

So I can tell you with some confidence it’s an ignition problem. How do I know, because you think it’s a fuel problem. A bit glib I know but been there as have probably most others here! Hopefully you have a multimeter.

I can promise you with 100 % confidence that Boyer and ignition systems in general do not like sitting about doing nothing. 3000 miles in 8 years.

I had exactly this problem and fixed it by going through EVERY electrical conection in the ignition system with a multimeter. Including cleaning the internals of the main and handlebar switches. Check any kill switch. I found three bad connections on my bike.

After that do the famous check of broken wires down at the Boyer pick up The wires break where they are soldered to the pickup plate. They look fine but break inside the plastic cover. This problem manifests itself by running and starting fine and then stopping after a while when it gets hot. When the bike cools down the bike starts again. Very frustrating.

On the Britbike forum John Healy has posted detailed instructions on Boyer checking. Do a search and I'll look for it too.

From memory his first line is " the day you fit electronic ignition is the day you cleanup your wiring "

Can't find the Healy one but this one looks good.


Note when you check the trigger plate wires give them a good pull and twist check. They can look perfect but broken inside

Next time it starts misbehaving pop the fuel cap, the vent hole may be plugged or restricted. Do this with great caution as an open cap and a few good bumps could turn you into a crispy critter. You won't need to have the cap open long, but do be careful.

Best

Bernhard said:

Screw right out , 15 pilot jet, points to the obvious, it's too small. Try a 25, screw it 1 half turns out, (set it to what your engine needs)

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Very likely he already has a 25 pilot jet, that has a 17 thou hole which is cleaned out by a 16 thou drill or guitar string. That a 15 thou guitar string gets through says it a 25 pilot not a 15 pilot jet. The 25 refers to the flow rate in cc per min not the size of the hole.

The premier pilot jet numbering is by size, so a 17 premier pilot has a 17 thou hole which is equivalent to the old 25 pilot jets and bush.

kommando said:

Very likely he already has a 25 pilot jet, that has a 17 thou hole which is cleaned out by a 16 thou drill or guitar string. That a 15 thou guitar string gets through says it a 25 pilot not a 15 pilot jet. The 25 refers to the flow rate in cc per min not the size of the hole.

The premier pilot jet numbering is by size, so a 17 premier pilot has a 17 thou hole which is equivalent to the old 25 pilot jets and bush.

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He said he has a Mk 11 amal carb

Mart, where in the U.K. are you?

Dave

Don't take offense, Are you sure you are operating the enrichener correctly?
Assuming you have the lever, lever up pushes the rod down, enrichener off. This is the run position.
Lever down pulls the rod up, enrichener on, choke position.

More than one person has been fooled by this.

The Mk II Amals come with #50 choke jets. That's way to rich, unless you live in Antarctica. A #35 works much better. Generally, a #25 idle jet comes stock. The mixture screw [controls the air, not the fuel] should be out 1 1/2 turns, plus or minus 1/2 turn. Otherwise, you need to change the idle jet, or locate the vacuum leak.

johnm said:

He said he has a Mk 11 amal carb

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Mk1 and mk2 pilot jets are 25 for 4 strokes, 25cc per min flow with 17 thou hole. They may be different shapes but the hole is 17 thou.

Welcome to the world of Lucas, Amal, Boyer and Norton. Don't get discouraged, Their are like women you have to learn what makes them happy, after that you have an enjoyable life!!!

When you filled the tank it started running badly, previously it was fine. When you drained the gas what did you do with the gas? Kill some weeds in the yard or put it back in the tank?

Fantastic response. Thank you. The original build sheet for the carb conversion, settled on a 15 pilot jet. That was changed to a 20 in 2019. So, I went back to a 15. When I got Berhard's reply, I thought I would swap back in the 20 jet I'd removed. It started, idled roughly, but with the pilot screw out about 5 full turns settled down and will tickover without stalling at about 1,000 to 1,100rpm. Progress. Thank you Bernhard.

I will order a 25 pilot jet tomorrow and believe that could be the solution.

On the ignition comments, I've not ruled it out, but I read previous threads and moved the wiring behind the points cover, it feels fine. Fingers crossed. It had a new wiring loom in 2013, but not a new kill switch.

I did open the fuel cap, to check, no difference, I also cleaned the cap and it leaked fuel on me when I tipped it up, flushing it out! Swooshdave (are you the utube guy? Like the channel), the old fuel was only a couple of days old from my fill up. I stood it in an old Jerry can for a day to settle and poured off the top 2/3 into the lawn mower can. The rest became weed killer. I didnt put it back in the bike, I bought fresh fuel in a clean can for the restart!

Dave, I'm in Essex. I've been emailing the local NOC coordinator, who's put me in touch with a local machanic who specialises in Brit bikes and rides a Commando. Once I've got it running, I'll get him to look it over for anything I've missed / safety check.

I was using the choke / enrichener lever the right way round, but easy to see how it could be confused. Not offended, worth raising.

Really pleased with the replies. Thank you, much appreciated. My feeling is, crap old fuel, low tank, muck in the carbs. Didn't work on reassembly because it was the wrong pilot jet. The pilot air screw is still too far out with a 20 jet, so I will get a 25. I plan a short ride to top the tank up tomorrow and will report back.

Mart

Mart UK said:

Swooshdave (are you the utube guy? .

Mart

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I see my disreputation proceeds me.

Have you checked for air leaks at manifold and or any jet screw o-rings?

One other thing to check in the carb is the choke plunger seal. The choke has a plunger, or piston, that seals off the fuel supply from the cold start circuit when the choke is ‘off’.

The plunger has a rubber seal in the end that can corrode / split / deform and thus fail to seal properly. When this happens the cold start circuit fuel can cause havoc with the carburation. The fact your air screw is 5 turns out got me wondrin’ if this might be the case (an attempt to weaken it to compensate for the over richness).

Its a 2 minute thing to check, so well worth doing.

Also, there is a myriad of needles and needle jets for mk2 carbs as many were used for two strokes and Triumph used some very unusual needle / needle jet combinations later on when they were fighting with emissions, so, worth checking in case a PO has inadvertently fitted something incorrect.

Finally.... IMHO it is ALWAYS sensible to change the spark plugs as a first step in ANY such running issues, especially on an old motor that might be running rich, burning a bit of oil and generally causing plugs to foul, and seldom gets ridden hard enough to burn them clean. Avoid buying cheap from eBay as counterfeit plugs are a problem. Buy a box at a time so you’ve always got new ones to hand when fault finding etc. I buy plugs from here:

Fast Eddie said:

One other thing to check in the carb is the choke plunger seal. The choke has a plunger, or piston, that seals off the fuel supply from the cold start circuit when the choke is ‘off’.

The plunger has a rubber seal in the end that can corrode / split / deform and thus fail to seal properly. When this happens the cold start circuit fuel can cause havoc with the carburation. The fact your air screw is 5 turns out got me wondrin’ if this might be the case (an attempt to weaken it to compensate for the over richness).

Its a 2 minute thing to check, so well worth doing.

Also, there is a myriad of needles and needle jets for mk2 carbs as many were used for two strokes and Triumph used some very unusual needle / needle jet combinations later on when they were fighting with emissions, so, worth checking in case a PO has inadvertently fitted something incorrect.

Finally.... IMHO it is ALWAYS sensible to change the spark plugs as a first step in ANY such running issues, especially on an old motor that might be running rich, burning a bit of oil and generally causing plugs to foul, and seldom gets ridden hard enough to burn them clean. Avoid buying cheap from eBay as counterfeit plugs are a problem. Buy a box at a time so you’ve always got new ones to hand when fault finding etc. I buy plugs from here:

Spark Plugs, NGK, Denso, Bosch, Champion | The Green Spark Plug Co

Spark Plugs UK Retailer NGK Bosch Champion Denso Bosch, Ignition, Fuel, Auto Electrical Wiring, Battery From Leading Brands. Also Stocking Modern Variants For Vintage & Classic Vehicles.

www.gsparkplug.com

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Reminds me of a situation a few summers ago when putting my 7 back on the road, recommissioned and off to the petrol station to fill up ready for a blast. On leaving the petrol station it started to run rough, returned home with the choke needing to be on, went over it, all the usual checks, nothing wrong but it turned out to be the fuel I had just put in. Replaced with fuel from another garage and away we went, sweet as a nut. You would never suspect bad fuel these days but, there you go.

Hi Mart
Whereabouts in Essex???
Great riding weather at the moment..... NOT!!!
:-(