Engine Misfire

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Jun 19, 2003
Recently, after I've been riding the bike for 30 minutes or so, the engine begins to misfire. Not frequently, probably no more than once every 3 to 5 minutes and it appears to happen on either side. The really frustrating thing is that it only seems to happen when I get the rpms up into the power band, meaning that "getting on the gas" sometimes makes it feel like you're "getting thrown over the handle bars" from the sudden deceleration.

This problem started on a ride back up from Laguna Seca to San Francisco and has persisted after a head rebuild. Not that I think the problem is caused by the head but we went through the carbs at the time and they checked out ok. It's a Combat motor running a Boyer ignition and I've replaced the coils. It idles fine, ~1100 RPM, and the plugs look nice. I've checked all the electrical connections in the ignition system and they seem solid. Neither coil feels significantly warmer than the other after a ride.

Has anyone seen this before? What can happen if a Boyer starts to go bad?

I once had a Norton S type that I mistakenly equiped with a Boyer electronic ignition. This bike soon developed symptoms similar to the ones you described. I replaced the Boyer with points and condenser and the problem disappeared!

I suspect your Boyer is at fault.


Charge your battery


Try charging your battery or replacing it if is old.
Boyers are great, but they do need a good battery.

Good Luck.
Hi Jeremy,

I saw this posted by illf8ed on anther thread, maybe your problem too???

"I put the Boyer on my '74 JPN and it worked fine. Watch out for the low tension wires coming from the inductor coils..these break inside the insultation due to vibration causing the engine to misfire at midrange"
If you have a bike that runs on a Boyer but misfires, Try this pull the points cover and with the bike idleing pull at the wires below the zip tie that is to be removed for Norton running. The following fix should be done in any case. A post from another board. Maybe it will help someone. --------------------------------------------------------------------------------
Only useing words can be hard. If you look at the Boyer plate that replaced the point plate you will see two wires coming out of that plate and a goob of epoxy holding them fast on the plate. Depending on the age of the unit you may find a nylon tie wrap around the same two wires at a mid point in the plate. Most of the time one wire will break at the tie, not all the way just a few strands at first. It's hard to find this break sometimes the bike will start and run well up to the point of a certain RPM, that is the RPM that is breaking the wire and will continue to as you replace every component on the bike. I have been thru this with seven bikes in the last two years only Commando's. So unhook the bullet connectors noteing witch wire is on the left and right holes in the plate. Cut the zip tie remove the plate from the bike after marking the timming location, I use a felt pen and than scribe a line in that mark. Now the plates in your hand small cheap lighter torch in other hand. Without ruining the circut board you must melt the solder on the back of the plate and pull the wires out. Reheat and useing a cotton cloth wipe away the old solder till the hole there is clean and clear. Repeat for other wire. This process finds the wire that is broken most if the time. Now you need a trip to the hardware, circut plate in pocket to find some short screws that will fit the holes in the board. They need to be long enough to go through the board and still fit two nuts on them. Also pick up some eyelet wire termanials that fit your screws, so, four nuts, two screws, two termanials, and two new male bullett conectors. Put the screws in the holes from the back to the front run down one nut and blue locktite in place on each screw. Now for more soldering, find an old piece of coax cable old TV stuff works and discect it till you have two short pieces of hollow braided wire, solder one end to the wire termanial and put some shrink wrap over that about one inch long crimp on the fresh male bullet connecters on the other end of the short hollow wires. Devise a color code for marking one of the new leads white or yellow electrical tape will do, a thin piece over the shrink wrap. Reinstall the plate, reconnect the wires now for the second set of nuts to hold the eyelett termanials down than the bullet connectors, and the hard parts done. You now need a small soft piece of foam to hot glue or silicone into the inside of the point cover that will keep the connected wires from ratteling Hope this works for you worked for me. Same simptoms as you cut out at mid to higher RPM's.

Just as important the power wire goes from the Boyer box to the coils and than to ground if this wire brakes or the ground wire from the motor to the frame brakes it can cause the same trouble. That's why I use a flat braided ground strap from the auto parts store to do the frame to engine connection. And make sure the coil wire is grounded at the top of that strap. norbsa
Wow there Norbsa!

That sure is a bunch of work just to make sure that dang ole Boyer gizmo keeps working.

What happened to the "set it and forget" that Nortonfan keeps talking about?

Are you guys sure that points and condenser are less reliable than a black box?


Hey Jason,

I have been running boyers for 25 years or more with no problem.

Maybe Boyer just sends the bad ones to you personally :?:

Then again, maybe it depends on whether you install it on the sidestand or centrestand.
It folds up out of the way on the centre stand but can scrape if on the sidestand :wink:

Like I said, I just set em & forget em :D

I really don't know why all the fuss about em, they are great unless you are into absolute technical things and argue the advance curve compared with Rita.

Maybe some people are a bit heavy handed when they are pulling the two wires through the points cover hole ?
Could this be the reason the lil wires are breaking on their systems ?

This is the only thing you need to really worry about and it's only the Commando's that do it to them. At least so far. The really old Boyers came this way from the factory screws and eyelet connectors. A friend has had one of these running in his Commando for 25 years and it has needed nothing. Sometimes the new ideas don't work. Any company that uses epoxy to hold wires is haveing a problem. But points should not be used by people who do not understand how to set an maintain them. Only the re-pop points are avilable, and for those with good Lucas points keep what you have because they out last the re-pops 10-1. The whole advance curve thing is being addressed by the use of the red box Boyer that can be changed to suite your requirments if you know what they are. Everyone that I know in Michigan that has a Boyer is told to turn on the key kick it slow one time and then kick it like you mean it. Seems to save the barked shinns and broken bones. norbsa

Just another one to throw in the ring.

On one occassion, my fuse holder had a break inside of it where you could not see it. Sometimes it was touching, other times not.

Looking at the fuse holder you could not tell, one of the connecting wires that goes in one end had a broken fittng on it. The break was just inside the fuse holder.

I had intermittent backfiring & other times loss of power.

It may have been one of the dreaded boyer fuse holders :wink:

By the way Norbsa, I can stand at the right side of my norton and kick start it first kick mostly with the kick start going through 3/4 of its range.

When you set em right it is the real meaning of life :D
No sore shin, no kickback, just a sweet running norton.

Glass fuses went out with points don't ya know. Kinda like running Lucas light bulbs when out for a long road trip. Little hard finding a replacment for the burnt one aye. norbsa
Now where does it mention "glass fuse", are you assuming ?


Have you had any luck solving this problem you have with your norton ?
Reg, you have had the rubberized buss fuse holder break? That's a new one on me. That slow kick thing is cheap insurance for broken bones only needs to happen once. norbsa

I think you had better read what I posted once again.
You are misunderstanding my post. Hint - "Wire" is the key word

I am more interested in trying to help people than discuss your personal choices of ignition etc.

Hi Jeremy,

I have a 74 Norton with a Boyer Ignition conversion - and I had exactly the same problem as you are having.

I had new carbs installed (the old ones were worn out in any case) and had the high voltage coils tested (they wre fine). So I went looking for an intermittant connection as this will signal the plugs to fire - most likely at the wrong time.

I found one loose connector on the black-yellow wire at the sensor plate where the points used to be. I soldered it to the wire and then proceeded to follow the Boyer wiring diagram and soldered every press-fit connector to its wire in the system. I cleaned the connectors as well. Since then the engine has run flawlessly - never missing over the last 3 seasons of riding.

There are other really good suggestions in this thread. Good luck with tracking down your problem.
So, as most of you guessed, it was an intermittant open in the ignition circuit for one of the cylinders. Now, I had checked all of the connectors (which were quite solid) but decided to pull the circuit board after noticing that I could "adjust" the idle +/- 500 rpm just by wiggling the wires. Discovered that tuning trick while broken down in the middle of the tollbooths on the Bay Bridge, what fun!

Short story even shorter, one of the wires had corroded through. Couldn't find it initially because it was hidden under the silicone my mechanic uses to strain-relieve the joint between the board and the wire.

anyways, i'm off to the hware store after work for some 4-40 washers to go with the mechanical fastenation between the ign. wires and the board.

thanks, folks, like always, it's been educational.
My favoite is when you have the key on pull on the wires at the plate and get the loud unexpected bang. Glad you found the bad wire. Your not the first or last. BTW this hardly ever happens to Triumph and BSA owners. Good time to check your timming marks with a dead stop and degree wheel. norbsa
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