Lost spark on one cylinder

Kjell

Kjell

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Suddenly lost spark on one cylinder. How much voltage am I supposed to measure on the negative side on the first of the two 6 volts lucas coils connected in series ?
 
Most of these EI's turn off the feed to the coils a few seconds after they detect the engine is not turning so the answer is 0V.

Assuming you have a boyer then follow the Boyer Troubleshooting guide.

Boyer Bransden Electronics Ltd - Fault Finding

www.boyerbransden.com

Note they do make the bland statement that a Boyer will either get both plugs sparking or none and if only one plug sparks the Boyer is not at fault. However their is one rare fault where the head earth back to battery can get compromised and only enough current flows enough for one spark (Boyer is wasted spark so both fire at the same time so needs double the flow of points). So when I suddenly lost one spark and all the normal fixes of swapping coils, HT leads, plugs etc did not work a supplementary earth wire from head steady bolt to battery terminal did.
 
Kjell said:
Suddenly lost spark on one cylinder. How much voltage am I supposed to measure on the negative side on the first of the two 6 volts lucas coils connected in series ?
Click to expand...
Assumming your connections and ground are good, you have a bad coil. If you think of the two coils as one and you have a positive ground, then the + of one coil is grounded and the - of the other has voltage when the EI provides it. One coil cannot have "power" without the other having it. That leaves only the secondary of the two coils separate (able to fail).

Ignition off, your meter set to ohms, lowest scale. Measure from the + of the coil with a ground wire to the + of the battery - must be 0 ohms. Then measure from the + of the coil with a ground wire to the head - must be 0 ohms. Repeat both with your meter on the highest ohms scale. For all four readings, ANY resistance is TOO MUCH. BTW, if using a digital meter with only one ohms scale, then use it and there are only two tests rather than four.
 
In the past I have had a coil go bad it was my left coil
Although it was still sparking but not passing current to the right coil
Very confusing at the time as the right coil had no spark and I changed it before realising it was the left one that was faulty
 
A bad ht lead could account for one side no spark. Try swapping left ht cap end to right plug and vis versa. If problem stays to left/original side then it is not the lead nor cap, nor plug.... coil likely.
 
baz said:
In the past I have had a coil go bad it was my left coil
Although it was still sparking but not passing current to the right coil
Very confusing at the time as the right coil had no spark and I changed it before realising it was the left one that was faulty
Click to expand...
While I agree, how does a coil know if it is right or left?
 
Everytime when I have lost one cylinder, it has been a HT lead, usually just falling loose at the coil.
 
baz said:
I used the left and right terminology that's all
I could have said one coil was dead but still sparking but not passing power to the other coil
Cheers
Click to expand...
We knew what you meant, installed position was implied via context.
 
marshg246 said:
Assumming your connections and ground are good, you have a bad coil. If you think of the two coils as one and you have a positive ground, then the + of one coil is grounded and the - of the other has voltage when the EI provides it. One coil cannot have "power" without the other having it. That leaves only the secondary of the two coils separate (able to fail).

Ignition off, your meter set to ohms, lowest scale. Measure from the + of the coil with a ground wire to the + of the battery - must be 0 ohms. Then measure from the + of the coil with a ground wire to the head - must be 0 ohms. Repeat both with your meter on the highest ohms scale. For all four readings, ANY resistance is TOO MUCH. BTW, if using a digital meter with only one ohms scale, then use it and there are only two tests rather than four.
Click to expand...
Excuse my ignorance but I see the terminology "head" is used when members talk about electric wiring.
The only heads I know of on my bike is the cylinder heads. Probably a stupid questions but still
 
kommando said:
Most of these EI's turn off the feed to the coils a few seconds after they detect the engine is not turning so the answer is 0V.

Assuming you have a boyer then follow the Boyer Troubleshooting guide.

Boyer Bransden Electronics Ltd - Fault Finding

www.boyerbransden.com

Note they do make the bland statement that a Boyer will either get both plugs sparking or none and if only one plug sparks the Boyer is not at fault. However their is one rare fault where the head earth back to battery can get compromised and only enough current flows enough for one spark (Boyer is wasted spark so both fire at the same time so needs double the flow of points). So when I suddenly lost one spark and all the normal fixes of swapping coils, HT leads, plugs etc did not work a supplementary earth wire from head steady bolt to battery terminal did.
Click to expand...
There is a Lucas Rita AB5 on the bike
 
Kjell said:
Excuse my ignorance but I see the terminology "head" is used when members talk about electric wiring.
The only heads I know of on my bike is the cylinder heads. Probably a stupid questions but still
Click to expand...
Greg is saying to ground the wire to the cylinder head, as it should a good ground point.
 
Kjell said:
Excuse my ignorance but I see the terminology "head" is used when members talk about electric wiring.
The only heads I know of on my bike is the cylinder heads. Probably a stupid questions but still
Click to expand...
Yes, the cylinder head is quite important to the ignition system. That's where the spark plugs live and if the head is not grounded there can be no spark!
 
You can get or borrow some long enough plug wires to connect the left coil to the right cylinder and vice versa and see if the misfire changes sides. You could also use two spark plug testers like this to do the switcheroo. Like others have said, it sounds like a bad coil.
 
Kjell said:
There is a Lucas Rita AB5 on the bike
Click to expand...
some Rita fault finding & troubleshooting tips:




Lucas Rita instructions

There has been a bit of discussion about the Rita system here. If anybody wants a copy of the original instructions for the AB5 and AB11 systems, they can be found here: http://www.triplesonline.com/techtips/Lucas%20AB5.pdf http://www.triplesonline.com/techtips/Lucas%20AB11.pdf
www.accessnorton.com www.accessnorton.com
 
Kjell said:
There is a Lucas Rita AB5 on the bike
Click to expand...
In short here's what happened. Noticed the bike was low on power but I did not hear any misfiring and it started on first kick.
Drove it home, parked it and put my hand behind the exhaust, right cylinder exhaust noticeable colder than left.
Pulled both plugs and it was obvious that the plug on the right cylinder was not firing.
Double checked with a few kicks - no spark
Suspecting the coil and since I had a brand new one laying around swapped I swapped the coil. Still no spark
Then I connected a test batteryt I use and put the positive battery on the minus on the right coil, then the negative on the battery to the + on the second coil.
Got a nice spark on the right cylinder.

Then I attempted to connect the minus on the first directly from the ignition switch since I figured I had a problem with my wiring.
The fuse blew and since then no spark whatsover.
 
Tornado said:
A bad ht lead could account for one side no spark. Try swapping left ht cap end to right plug and vis versa. If problem stays to left/original side then it is not the lead nor cap, nor plug.... coil likely.
Click to expand...
Tried changing the coil since I had a brand new one laying around. Still no spark
 

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