intermitent spark on right side

Craig · Dec 10, 2009

Hello all ; while I've used this site since' 04 I rarely make a post... I really enjoy reading and learning . My problem is a persistent miss on the right side. The commando is a 1972 combat . Useless fixes so far compression test ...Good ,new coils, wires, and plugs , switched from single 34 mm mikuni to two 32 mm mikunis ( that was fun ) and have switched from side to side wires ,coils and plugs. Brutus (her name ) had boyer electronic ign. installed when I got her and I estimate it is from early to mid 1980's . The head had been done before I got her and a hotter cam installed ? ( unknown type or make ) When setting up carbs I thought I could lean out mixture to cure the fouling plug so far I have some improvement .Since winter has come and brutus is in the shed I thought I might get it right this time with help from your expert brains . Any suggestions would be great . I have never set timing but usually Brutus starts first kick ... brutus' personal info is V.I.N. 207384 APR 1972 Thank you to all who take the time to read and respond !!!

Craig
Truro N.S. Ca.

Jeandr · Dec 10, 2009

When did the trouble start :?: (if I can read correctly, you switched to dual carbs after the problem started am I right :?: )

Is it possible there is an air leak on the right side :?:

Did you vote for Stephen Harper :?: :wink:

Jean

Craig · Dec 10, 2009

Hi Jean
Yes the switch was made to try fix the problem .When I stripped the bike down after I got it home I noticed the spark plugs were different but it didn't register as a possible sign of trouble and no I didn't vote for S.H. but nobody did when you ask them , I don't know how he got control with so few votes . I can tell you when she's running good she runs real good. I use NGK BPR7ES on both sides.What is a good test for air leak ... wd40 ?

JimC · Dec 10, 2009

The Boyers have an all too frequent problem with the wires from the pickup coils breaking. The break occurs inside the insulation near the solder point, so it's impossible to detect visually. If your bike starts and runs on one cylinder, but after ~3000 rpm the miss disappears you can pretty well bet it's one of the wires from the Boyer pickup coil. There's a ton of info here on the infamous Boyer wire fracture problem and how to fix it.

likebikes · Dec 11, 2009

I had the same problem. It drove me nuts!
Check the ground wire on the Boyer and coils. I ran a wire back to the (+) battery. Bonded the engine to the frame with flex wire.
That was it. FIXED!
Let us know if this was the problem.
dave

Craig · Dec 11, 2009

Thanks Dave for the response...I made up my own wire loom for Brutus while rebuilding and I'm pretty sure as an after thought I ran a "dedicated ground" from engine at head steady bolt back to the battery.
Is this what you mean?
Craig

maylar · Dec 11, 2009

You've touched pretty much everything but the Boyer ignition module. As already suggested, check the wires going to the stator board inside the points cover. Not only do they tend to fracture at the PC board, but they also chaffe against the crankcase where the wires enter the points cavity.

It seems odd that only one cylinder is misfiring though. Ignition problems would normally affect both cylinders since the coils fire at the same time. Possibly a funky magnet in the Boyer rotor. Also possible to have a sticky valve. Does it miss at all speeds or just at idle?

JimC · Dec 11, 2009

If only one wire from the Boyer pickup coil is fractured it will miss on one cylinder.

Jeandr · Dec 11, 2009

JimC said:
If only one wire from the Boyer pickup coil is fractured it will miss on one cylinder.

What is the logical explanation for that? The pick-ups give a pulse for each revolution of the motor, both coils fire at the same time (if two coils are used of course). I can understand a miss on both cylinders if the pick-ups or the Boyer itself are involved, but only one side :?:

Now if the pulse from the pick-ups was not timed correctly, I could understand, the Boyer depends on the two coils and the two magnets being exactly 180 degrees to each other and the resulting pulse occurring at the right time when it is needed by the corresponding cylinder.

Craig said he swapped everything that could be swapped and the miss was still on the same (right) cylinder, to me this means something still on the same side has not been changed, this leaves a lot of mechanical parts like pistons and valves, push rods, followers and camshaft, then there is the induction system, valve adjustment...

Jean

JimC · Dec 11, 2009

That's exactly what happened on my Commando. Try it yourself.

Jeandr · Dec 11, 2009

JimC said:
That's exactly what happened on my Commando. Try it yourself.

Well, I'll be :!: Call me a doubting Thomas but I still find it hard to believe. This may be a good reason to switch to a better electronic ignition :wink:

Jean

JimC · Dec 11, 2009

I would add, I was using a Dyna coil.

norbsa48503 · Dec 12, 2009

"I have never set the timing" says it all to me. Until you have strobe timed the machine and watched the behavior of the line under the light you have no reference to go forward . Always one flame will go out before the other when a base line adjustment has been ignored like timing or float bowl height. You have to get these set before proceeding. You may be dealing with a new bad plug, it happens. I have Boyer kits if you need one.

highdesert · Dec 12, 2009

maybe, the timing is too far advanced?
don't know if works in theory, but in reality this was the case of a mis firing for me

Jeandr · Dec 12, 2009

I know sometimes a simple basic adjustment will need to be done to fix what appears to be something else. Years ago, a friend had a Datsun 510, the thing would start at a quarter turn everytime except when the temperature went below -15C (5F) then it would need to be boosted for up to 30 minutes, ether pumped in the carb... The shop changed all the ignition system, the carb, the fuel pump... until one day they checked the valve lash which was a few thou too tight, after that, no more problems.

Jean

likebikes · Dec 14, 2009

Hi Craig,
Run a dedicated wire from the (+) side of the coil (the one with the red wire from the Boyer) to the (+) battery terminal.
Bond motor to frame with flex wire. I had a bad connection here and it caused misfire on the right cylinder just as you described.
I have no explanation of why this affected only one cylinder, but maybe has something to do with wiring the coils in series.
Here is a one line.
Positve ground one is on the bottom of the page.
http://www.britcycle.com/Manuals/Boyer_pos_neg.pdf

Craig · Dec 15, 2009

Thanks to all , for all suggestions ; I will make new pick-up leads ,time with a strobe and check my valve lash adjustment. Any other ideas are welcome and will I report back with my results.
Thanks again and HAPPY HOLIDAYS!!!! to all members of Norton Nation
Craig

Paul1972 · Aug 7, 2010

Hey Craig,

I was just wondering if you found out what the problem was.....I have the same snag

rick in seattle · Aug 7, 2010

Craig,

Focusing on the Boyer when the problem is with a particular cylinder is a waste of time. The Boyer output (like all other EI systems) is COMMON to both coil inputs and results in a wasted spark. Both coils are driven simuiltaneously by the same EI output. EI failure must affect both sides of the bike equally. Your problem lies between the coil inputs and the spark plugs (if electrical) or fuel delivery (which, with dual carbs, is inherently non-symmetric), or, less likely, exhaust. Running a Dyna dual coil system makes the IE scenerio even more unlikely, as the coil inputs are common. Pull the plugs, positively ground (with test leads) the plug cases to the head, turn off the lights, and confirm that both plugs are sparking at the same time when the engine turns over. While this test doesn't guarantee that the plugs are working at high ignition pressures, it is a strong enough indicator to move on to fuel problems. Checking the input and exhaust valves is the next easiest thing to do. Saving the carburettors for last is, IMHO, a wise course of action.

dorteerts · Aug 9, 2010

One can only hope the problem was solved otherwise it has been a long frustrating eight months!
Just as an aside, when I first got my Commando it was fitted with a brand new Accel Super Dual coil (receipt came with bike) and a Boyer. After one week one of the coil primaries failed. Would fire fine on one side not on other. Simple coil lead swap found and isolated problem quickly. Was replaced under warranty with no hassle (East Coast Custom here in Oz, nice people to deal with). In the meantime I went with some original type high voltage Trispark coils I had bought for the Bonnie and not yet fitted. They have been excellent. I still have the new Accel in it's box and may refit one day (or sell/give to one of my Harley mates). :mrgreen:

intermitent spark on right side

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