Norton Commando MK 111 ES Misfire/Backfire

Hello, I have recently acquired a Mk 111 ES Commando, it is in superb condition and only covered 18,000miles. When I started it for the first time, although it started easy, it had a bad misfire on the LH cylinder and when revved to around 2,000RPM also backfired badly on this side. When warmed up it runs slightly better but if I hold my hand over both exhaust outlets the LH gasses are colder than RH and are uneven(so the silencer is cooler on the LHS. I have checked the Boyer ignition and that seems OK, I have also swapped the plug/coil leads over and fitted new plugs and moved the stator plate through 90 to eliminate a suspect pick up coil. I still have the misfire on LHS. I have checked the carbs which are new and re set them. The Battery is new and fully charged. I have checked tappet clearance which was spot on. I now suspect that the problem may be a sticking valve as the bike had been off the road for over 10 years until last summer and has only done a few miles since. One last thing if I rev the engine by quickly opening and shutting off the throttle in around 3-4 sec cycles to 4,000 RPM it seems good and does not misfire or backfire.
Any suggestion? thanks

This site is full of posts about the Boyer causing the exact problem you are having. A search will probably provide the fix you need.

yes many posts about the lead wires breaking from the back on the plate, must remove to check tho. Also i would do a compression check cold with the throttle WOT and see what your left side shows. MUST BE WOT

With the carbs there are many small things that make a large impact. From your post it doesn't looks like you have actually rode the bike yet, you are just running this on the center stand? If so, most of what your doing can be focused to the idle circuit.......so far. I would first check the pilot jet, then throttle needle to make sure it hasn't fallen out of the clip AND the position of it. You said they are new but did you do the work and can verify or someone else??

Also fuel petcocks not allowing enough fuel, filters if you have them, all can collect swarf and choke off fuel supply causing a lean condition. Most of the time that only becomes prevalent under a load though, not while your zinging the engine away on the center stand.

There are ALOT of good posts about carbs and sites we can direct you to when you get to that point.

Jaymac,

I'm with Gavin on the probability of carbs. They may be new, but I had a very frustrating episode with a Mk2 850 with new Amal replicas and the lefthand cylinder was playing up in a similar manner to yours. After exhausting all possible electrical causes, and blowing air through jet passages (which indicates some flow but NOT the actual volume), I stripped the LH carb and found machining swarf trapped between the main and needle jet. In addition there is a suspect dud Pilot jet and the float setting was out and the tickler plunger was set too high to flood the carb as well. Pretty abysmal for a new product.

However, I am pleased to say the manufacturer in the UK has offered to investigate the problem and supply new carbs. They are concerned and taking the right approach to rectifying the quality issues.

Mick

Ninety-five per cent of carburetor problems are electrical. I would definitely eliminate the Boyer pickup wires before I started delving into the carbs. From what you posted I'd give pretty good odds it's electrical. The pickup wires in particular.

JimC said:

This site is full of posts about the Boyer causing the exact problem you are having. A search will probably provide the fix you need.

Click to expand...

Thanks Jim,it did seem like a Boyer fault. I have checked out the Boyer from their fault finding guide and it looks OK, also checked pick up coils on stator which also were giving correct reading and as a final check I rotated the stator through 180 so that the coil with the timing holes was now in the position of the other coil(which I had assumed if the coil or wires were faulty would transfer the fault to the RH cylinder) but the misfire was still on LH. I also have swapped over the plug leads to check coil 1&2 but still have same fault. As both spark at same time is it possible a fault with black box?

GavinJuice said:

yes many posts about the lead wires breaking from the back on the plate, must remove to check tho. Also i would do a compression check cold with the throttle WOT and see what your left side shows. MUST BE WOT

With the carbs there are many small things that make a large impact. From your post it doesn't looks like you have actually rode the bike yet, you are just running this on the center stand? If so, most of what your doing can be focused to the idle circuit.......so far. I would first check the pilot jet, then throttle needle to make sure it hasn't fallen out of the clip AND the position of it. You said they are new but did you do the work and can verify or someone else??

Also fuel petcocks not allowing enough fuel, filters if you have them, all can collect swarf and choke off fuel supply causing a lean condition. Most of the time that only becomes prevalent under a load though, not while your zinging the engine away on the center stand.

There are ALOT of good posts about carbs and sites we can direct you to when you get to that point.

Click to expand...

Thanks gavin, I did check the carbs(needle setting, slides, main jet,etc) but I had assumed that as they were only 6 months old and had not had any use the would be OK but from your reply and others i have seen this may not be the case.

ML said:

Jaymac,

I'm with Gavin on the probability of carbs. They may be new, but I had a very frustrating episode with a Mk2 850 with new Amal replicas and the lefthand cylinder was playing up in a similar manner to yours. After exhausting all possible electrical causes, and blowing air through jet passages (which indicates some flow but NOT the actual volume), I stripped the LH carb and found machining swarf trapped between the main and needle jet. In addition there is a suspect dud Pilot jet and the float setting was out and the tickler plunger was set too high to flood the carb as well. Pretty abysmal for a new product.

However, I am pleased to say the manufacturer in the UK has offered to investigate the problem and supply new carbs. They are concerned and taking the right approach to rectifying the quality issues.

Mick

Click to expand...

Thanks Mick , sound like you had the same sort of problem i will check the LH carb again as you suggest. I have now seen a few posts with the same sort of problem with new carbs.

These links should explain it all in addition to what has been previously posted:

Boyer: http://www.ntnoa.org/engine.htm
(Wiggle and pull on wires vigorously while checking trigger coil resistance at the coil end of the wires.)

Amals: http://www.jba.bc.ca/Bushmans%20Carb%20Tuning.html
(Especially idle jet passage cleaning - reaming. I had this problem over the summer and it backfired like crazy when first starting.) Also the modern 10% alcohol gas goes bad really fast. I use Stabil marine version.

Good luck.

Russ

Jaymac,

I rotated the stator through 180 so that the coil with the timing holes was now in the position of the other coil

Click to expand...

The Boyer stator coils are excited at the same time, turning the stator over won't change anything. However try swoping the plug leads over and see if the problem goes to the right cylinder.

Could be a coil.

Cash

Thanks Cash, but I swapped the pickup coils as I was running out of ideas, I had already tried swapping the plug leads and the misfire was still on the LH cylinder.

batrider said:

These links should explain it all in addition to what has been previously posted:

Boyer: http://www.ntnoa.org/engine.htm
(Wiggle and pull on wires vigorously while checking trigger coil resistance at the coil end of the wires.)

Amals: http://www.jba.bc.ca/Bushmans%20Carb%20Tuning.html
(Especially idle jet passage cleaning - reaming. I had this problem over the summer and it backfired like crazy when first starting.) Also the modern 10% alcohol gas goes bad really fast. I use Stabil marine version.

Good luck.

Russ

Click to expand...

Hi Russ, thanks for that, I have already tried trigger wires etc on the Boyer. I will now check the LH carb thoroughly especially the idle jet passage. This point has also been made by Mick and Gavin who also have had problems with new build Amals.

I had the same problem and I found the answer here in the forum.
Check for bad ground.
I ran a wire from the coil to the battery (+) earth cable and installed a braided flex wire from the head to the frame up by the head steady.
The problem started as intermittant then becames continuous with the same symptoms you are experiencing.
She runs like a charm now.
Let me know what you find.

likebikes said:

I had the same problem and I found the answer here in the forum.
Check for bad ground.
I ran a wire from the coil to the battery (+) earth cable and installed a braided flex wire from the head to the frame up by the head steady.
The problem started as intermittant then becames continuous with the same symptoms you are experiencing.
She runs like a charm now.
Let me know what you find.

Click to expand...

Thanks for that, the first time I tried to start the bike it took around 10 kicks which I forgot to mention on my first message. Once started it misfired and backfired and would not tickover and even when warm it still took 5 or 6 kicks to get it going. I called the bloke I bought it from and he said he had not had a problem with misfire(well he would wouldn't he) he also said that there was a art to starting it and not to use choke even from cold! I then removed the tank and investigated the Boyer wiring to coils etc as their fault diagnosis suggested this is where the problem could be. All the wires were connected OK and the coils checked out also but when I was checking the earth connection to coil 1. the wire pulled out of the connector which was the original earth wire to the wiring loom. The wire was blackened and obviously the solder was aged and I assume due to a dry joint to the pin. So I removed the pin and made good the joint and resoldered, I also included additional earth wire from this +ve connection to the coil to the frame. Once I had corrected this earth connection the bike fired 1st time
from cold with full choke, and 1st or 2nd when warm also it ran much more even and would tickover fine. However I still had the misfire/back fire on LH cylinder so I assumed I had not cured the problem. On reflection the poor earth was causing part of the problem but there was another fault. I think that I will take your advice and make sure that I have a good earth connection to the engine as their is corrosion on the earth tag on the engine bolt. I now am in the process of stripping down the LH carb to check out the pilot jet etc as a number of replies have mentioned that the new Amals build standard is not that good. So I believe that I have had two faults contributing these problems. If all goes well I hope to take the bike on the road for the first time tomorrow, I will let you know how I get on.
Cheers

Thanks to everyone for your help, it has enabled me to sort the problems in just a few days. I wish I had found out about this website earlier it's by far the best.
I took the bike on the road today for the first time weather was OK sunny and roads were dry although it was only 4.5c. It started first kick with full choke and I started off straight away, once underway it ran fine with no misfire or backfire I did not venture too far from home just incase. After about 1 mile the engine was warmed up enough to take the choke off fully, I was cruising at around 70mph(around 4,000RPM) and it pulled well up hills and felt very smooth. After about 15 mins I returned to base to check things over, just as well as the right exhaust had worked loose(the locking tag was not engaged properly). After tightening the exhaust ring and securing the tab correctly ( I will lockwire them together later) I looked it over for any other snags, as it all checked out I set off again. This time I went a bit further, around 20 miles and it ran perfect no misfire and no popping from the exhaust or back fire on overrun. I had forgotten how good the Commando is to ride, it is around 25years since my last one and I have only had modern sports Italian and Jap bikes since then.
So I now know when I got the bike it had two problems one was a disconnected earth to the Boyer(coil 1.) and the other was with the LH carb idle jet blocked. As the misfire was still there after I found the bad earth on Boyer I had assumed that ther must be another fault the the ignition. As I had a number of replies which said that they had problems with the new build Amals I cleaned out the slow running as suggested and found some crap.
So thanks again for all the help, atleast I have found out quite a bit about Boyer etc. I will post up some pics of the bike in the next few weeks.
Cheers

I'm glad it all worked out for you - look forward to seeing the pics!