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ET: Engine (Twin) No Spark

brian gains

Well Known and Active Website User
VOC Member
Twin plug heads fitted with twin spark DynaTek coils and EI. The rear pot only cuts in when I make the spark jump between plug cap and plug, I've only tried this on one of the rear plugs. I can only think that both rear plugs have fouled, any other ideas.
 

Marcus Bowden

Well Known and Active Website User
VOC Member
Do not fit a double-ended coil to same head as it will only fire one plug. Struggle all the way to London and back once so over retarded and plugs went blue.
 

Robert Watson

Well Known and Active Website User
VOC Member
Are the dynatec coils the right resistance. I ran them on a Lucas Rita electronic ignition. They would go about 2500 miles and then go on one cylinder and eventually die completely. The new set said 3 Ohms but when I tested them they were only 1 1/2. The rita burned them out.
 

brian gains

Well Known and Active Website User
VOC Member
I was provided with a 'sketch' of the ignition and it indicates that each coil fires the front and rear pot.
Same as Robert, running Lucas RITA I picked up the bike late last summer so not 100% familiar with it. The supplied paperwork has a Mistral Eng' ignition diagram that indicates 17M6 coils (?). DYNATEC paperwork states coils available 5ohms DCS 8-1, 3 ohms DC1-1 , 2.2 ohms DC4-1 and 1.5 ohms DC2-1.

The ones that should be fitted are the 3 ohm then, rather alarming that quality control allows coils of only 50% of the specified resistance.

I guess testing the resistance is as easy as setting the resistance range on meter and shoving probes in between input and output? 3 ohms being the desired reading give or take 10%.

I don't recall any specific identifying stamps on the coils but then haven't inspected that closely. If coils read OK I guess I'm looking at plug and more likely carb if the plug is fouling however they did not look too bad to me. I'lll have another ferkle and update.
 

Robert Watson

Well Known and Active Website User
VOC Member
I queried back in the day if there was a + or - on the coil as nothing was marked and I was told that it did not matter which way round it was connected. I do have an old (I think unused) coil from back then and it is marked 3 ohm, and i just checked it and it measured 3 ohms between the terminals. I fought that unit quite a bit as they wanted two big Lucas 6v coils in series which would have meant having two big ugly coils hanging off the engine somewhere. Also when it is running it draws a lot of power and I think that contributes to the coils overheating and self destructing. I ended up using really cheap coils from an Onan 2 cyl genset as they were pretty cheap and I could buy them in just about every small town in North America that had an auto supply store, which is pretty much all of them. Always pack a couple on a trip and with great regularity they also lasted about 2500 miles even with the mag cover off for extra cooling.

Eventually I used the Mistral housing and adapted it to run Harley electronics. If I think of it I change plugs every 40 or 50 thousand miles. It has NEVER skipped a beat, and I haven't touched it since about 1993 or so.
 

brian gains

Well Known and Active Website User
VOC Member
in close on 50 years of biking I've only ever ha one pair of coils go south on me, does that mean i'm overdue? whatever, when I picked up the machine it started and ran as sweet as a nut, although apparently it had been standing for some while. I've been through the carbs. although this issue started before. I'll look at the resistance on the coils and maybe change the plug diet.
 

Bill Cannon

Well Known and Active Website User
VOC Member
Are the dynatec coils the right resistance. I ran them on a Lucas Rita electronic ignition. They would go about 2500 miles and then go on one cylinder and eventually die completely. The new set said 3 Ohms but when I tested them they were only 1 1/2. The rita burned them out.
Forgive me if this is obvious but are you aware that if two 3ohm coils are wired in parallel the combined resistance is half, i.e. 1.5ohms?

Cheers
Bill
 

Robert Watson

Well Known and Active Website User
VOC Member
I do know that but this is a single double ended coil and fires a lost spark on the other cylinder
 

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