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Original Post (Thread Starter)
#867141 12/23/2021 10:30 PM
by Hugh Jörgen
Hugh Jörgen
Having installed new Amal 930's on the Norton, proceed to set-up.
Follow Bushman's procedure.
Start engine, intermittent miss and backfire on D/S, was running normally before carb replacement.

OK, back to first principles, start with checking timing.
Strobe normal on T/S, reflects misses on D/S.
?? Pazon is wasted spark, so either none or both sides should strobe the miss?

For more confusion on my part, back in 2013 Kommando wrote:
"I had the same as Rohan, boyer only sparking on one side, a dedicated earth lead from head back to battery cured it."
So a wasted spark system can misbehave on one side?
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#867167 Dec 24th a 07:01 AM
by DavidP
DavidP
Originally Posted by Hugh Jörgen
Having installed new Amal 930's on the Norton, proceed to set-up.
Follow Bushman's procedure.
Start engine, intermittent miss and backfire on D/S, was running normally before carb replacement.
Then I wouldn't be looking at the ignition. There are many little things which can go wrong with a carb installation. Sounds like a small intake air leak to me.
2 members like this
#867373 Dec 27th a 05:03 PM
by kommando
kommando
Originally Posted by Hugh Jörgen
This is what lost me after reading Kommando's comment from 2013.
How does an engine ground function for one and not the other?

On dual coils one coil is wired opposite polarity to the other internally so ignition spark current stays within the coil/head loop and so both always fire if the coil is good.

On twin coils you have a full loop including the battery.

With wasted spark you have double the ignition current than with points, on my bike the engine earth wire was failing and so when 2 coils fired there was not enough capacity for 2 sparks but enough for 1 spark so only one plug sparked. When I added the dedicated earth the capacity for 2 sparks was restored.

What gave me the idea was when I took the HT off the 'Good' coil and started the bike on only one cylinder the 'Bad' coil sparked well with none of the previous backfiring or no spark.

Quote
New N7Y's gapped .028.
Swapped HT leads. No change.
Coils are 2 6V PVL's in series. Swapped in spares. No change.
Checked/snugged trigger wire terminal block screws. No change.

I did all that and changed EI completely, all made no change until I left the HT lead off the good coil and then I realised there was an issue further down the path and added a new earth wire, instant restoration of 2 sparks.
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