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Ignition

Bill Thomas

Well Known and Active Forum Website User
VOC Member
Greetings, Can anybody help, I have Rita ign' 12v useing 2 6v mini coils in (series)?. I broke down a long time ago, Faulty front coil, I was lucky to have in my bag a 12v mini coil, Started well and got home ok, But slow running was changed i.e. faster. Spoke to the Rita man,told him I didn't like small coils, Had trouble years ago,He said use 12v double coil, "But it will not rev' past 5800" Thats OK I said. He sold me one and it's been on for some time,It always started better with 2 6v coils, (Why) ?. I know that putting 2 6v batteries in series gives you 12v but i can't work out how much power goes to each 6v coil ? and what happened when I used one 12v and one 6v to get home, Rita man said it did no damage. Am thinking of going back to 2 6v but I need to no why, Please keep it simple as my head hurts !! Cheers Bill.
 

Matty

Well Known and Active Forum Website User
VOC Member
Hi Bill-
As an electrical Engineer I'm a bit puzzled by your query if you have a V Twin Vincent because the two 6v coil system you describe is usually associated with parrellel twin bikes - like a Triumph or Matchless/AJS and produces sparks for each rev of the engine one of which is "wasted" on the cylinder which is on the induction/exhaust stroke. However I am not very familiar with the Rita system and there may be some "Magic" wasted spark version which can be used with a Vtwin - though I can not imagine how !! Triumphs also used a system with two sets of points and two coils, ie a separate set of points and coil for each cylinder - a horrible system because you had to set the timing of each spark individually and as the points wore differently, the ignition timing changed between the two cylinders!!
.


With a parrellel twin the two 6v coils can be substituted with one 12v coil which has each end of the high voltage side brought out - one to each cylinder to produce a wasted spark electronic system as used on most Japanese twins, fours and 6s, with one, two or three coils as appropriate.

If one set of points are used on an older bike,with a wasted spark system they need to have either a double lobed cam if it rotates at half engine speed or a single lobed cam running at engine speed .


I do not believe a wasted spark system can be used on a Vtwin because the cylinders do not fire at 180 degree intervals, though it may be possible for an electronic substitute for points to provide two outputs at the correct timing intervals to drive two separate 12volt coils - one for each plug.


If in fact the bike you refer to is a parrallel twin and had two 6v coils in series, then if one coil was substituted for a 12v one, the the current would be reduced and you would get a poor spark from both coils because the 12v coil would have about 8v across it and the 6v coil only 4v - the bike would probably run, but the sparks would be much less than ideal and could cause poor running.

Hope this may help and not cause too much confusion.

Matty
 

Matty

Well Known and Active Forum Website User
VOC Member
PS -Read this in conjunction with my previous reply.

Having thought a bit more about a wasted spark system for a Vtwin, I believe it would work with two pulses to the coils from the Rita at unequal intervals to accomodate the 50degree differernce between the two cylinders. The "wasted" sparks for the cylinder not firing would then not happen at 180degrees but would still not do anything to this cylinder which would not be on its compression stroke.

Two 6v coils in series should however perform the same as one 12v double ended coil (obtainable from Goff) but my thoughts about one 6v coil and one 12coil in series remain the same - ie. you will have a weaker spark to each cylinder,- though why this causes the tickover speed to change is a bit of a mystery.

Matty
 

Howard

Well Known and Active Forum Website User
VOC Member
Bill

I don't know about the Rita, but my Pazon uses the wasted spark principal. Pazon say 2 12 V in series is ok, but two 6 volt in series or a double output 12 v coil should be used on racing and high compression engines.
PM me your email address and I'll send a copy of O&Ms if you're interested. I tried to PM you the info but I don't know how to do attachments.

H
 

Bill Thomas

Well Known and Active Forum Website User
VOC Member
Hello Matty, Thanks for your help,The Rita is for a Vin twin, I bought it from VOC about 6 years ago. It has worked well with 2 6v coils but after a few hundred miles I broke a cam follower and it was off the road 2 years ish, I was running TT carbs, It's my old L/ning racer, I thought the volts might be like you said 8 and 4ish but the slow running went up so I thought it must be getting a better spark, It has a single lobed cam, But they started putting stuff in the petrol about this time so I lost my way a bit. Am now running 28mm concentrics, Another mistake !! I am getting the carbs better by the day but starting after a 20 min' stop is like the old days with a Mag'. I am just off to Netley boot fair so i might pick up a couple of 6v coils and try again. The Rita man says with 12v coil it has a 5800 rev limit so it is not the same !! Cheers Bill. Hello Howard It's bill.thomas@fsmail.net Not sure I will understand it but thanks, Cheers Bill.
 

Matty

Well Known and Active Forum Website User
VOC Member
Two 12v coils in series would need 24v volts to work properly so it must be two 6v coils in series for your 12v system.

Don't really see why a double ended 12v coil from Goff should be rev limited unless they are using a cheap form of iron core which does not work at high frequencies (I used to design transformers and inductances in the 1950s in my early electrical reseach careeer) and had to think about these details then. The Rita man has no doubt done some experiments, so you have to believe him when he says it will not work properly above 5800 revs - which coincedentally was the limit put on the old style crowded roller Vincent big ends!!.
However a Japanese 12v double ended coil should be fine - they are designed to work at much higher revs than a Vincent could ever go.

Best of luck.

Matty. mattynjane@btinternet.com
 

bmetcalf

Well Known and Active Forum Website User
VOC Member
Harleys have used wasted spark coils since the '70's, so the wasted spark must occur before the mixture is rich enough to be persuaded to ignite. The RITA needs a coil in the right impedance range to work. I called Mistral Engineering and they told me the right impedance as an alternate to their standard 2 coils in series. I am not at home now, but will look up the number and post here. (I bought my RITA from Kemps maybe in the 80's, but my mag has done so well - touch wood - that I never put it on the bike. I even have a Phil Primmer GRP mag cowl to mount the coil!)
 

Matty

Well Known and Active Forum Website User
VOC Member
A good point Bruce - the Rita electronic system could well require a coil with different characteristics from one used with points and a capacitor. This could mean a different DC resistance and possibly inductance from the ones used by an old points based unit.

However the Japanese and Bosch units with double plug connections are designed to work with electronic ignition systems and could possibly work OK. To be safe however it would be best to use a 6v coil which is the same as the good Rita one left on the bike. If you can identify the good coil as a standard unit it may be easier and cheaper however to buy one from a normal motorcycle parts dealer.

Good Luck

Matty
 

Bill Thomas

Well Known and Active Forum Website User
VOC Member
Hello All, Thanks for your input, My double coil came from the rita man, I spoke to Goff the other day, Didn't get on with him,he may have had a bad day, Or as the wife would say It's Me !! Good bit from Howard, His bloke says"A higher resistance coil may give slightly less spark, But will draw less power", Come to think of it ,Befor with 2 6v coils, The ampmeter gave a bigger discharge when switched on, I asked Goff what the resistance of his coils was and he said he didn't know !!. So Matty have I got to look for a low number resistance ?, Unlike Howard I am not worried about it taking too much power because I have a flash Alt' from the USA, I don't know what the resistance was on that 12v coil I used to get home with, Maybe that was why It ran faster ? When the bikes going it goes like stink, I thought with 28mm carbs it would be slow, But not a bit of it !!. Thanks Again Bill.
 

Matty

Well Known and Active Forum Website User
VOC Member
Yes old Goff can be a bit grumpy at times and not very helpful. Your best safe solution I am sure is to buy another 6v coil of the correct specification from Rita - though there is always the risk that they would charge you for a special coil when it is just a standard cheap unit with their label on it.


Sorry I am just a bloody old cynic who has seen most of it before!!!

Matty
 
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