750 sf ignition problem

Lyndoneil

Lyndoneil

Full member
Location
Towcester uk
Hi knowledgeable ones.
Slightly perplexed! I've a sf2, was fine 2 weeks ago when I parked it up. But now it's only firing on the right cylinder.
It has a Boyer mirco_mkIII ignition system (Not fitted by me), with a duel outlet Wat Yong coil, (which in itself does not fill me with confidence, but what do I know, it might be the Ferrari of coils)
It's firing fine on the right cylinder, have changed plugs and caps, makes no difference.
I'm rather under the impression that the coil is very unlikely to fail on one cylinder only and if it fails then it should be both. Any ideas?
By the time I get replies I guess the bike will probably be in a thousand bits.
 
Appears the Boyer mirco_mkIII ignition system is working or both plugs would not be firing. I take this a Pointless ignition system. See if both plugs will fire on the side that works to eliminate a possible bad plug and if both plugs do not fire on the none working side I would suspect a bad plug wire, coil or one of the electronic trigger distributor pick ups. 750's came with dual points. Sometimes when one side doesn't spark, excluding the aforementioned electronic modules, can be attributed to Point Gap or a bad Condenser.

The wire from that side of the Coil feeding to ground through trigger may be broken or disconnected.

This system appears to have Magnetic Triggers - Is this coil a dual in one pack container ??

www.britishbikebits.com

KIT00052 Boyer MKIV Ignition Kit - 12v Twins BSA, Triumph - BBB

Boyer Bransden MKIV Ignition Kit - 12v Twins BSA, Triumph
www.britishbikebits.com www.britishbikebits.com


I always preferred points Vs Electronic Units for twins - Especially kick Starters - as they never seemed to provide enough spark to get them started or idle correctly.
 
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Laverda SF said:
Appears the Boyer mirco_mkIII ignition system is working or both plugs would not be firing. I take this a Pointless ignition system. See if both plugs will fire on the side that works to eliminate a possible bad plug and if both plugs do not fire on the none working side I would suspect a bad plug wire, coil or one of the electronic trigger distributor pick ups. 750's came with dual points. Sometimes when one side doesn't spark, excluding the aforementioned electronic modules, can be attributed to Point Gap or a bad Condenser.

The wire from that side of the Coil feeding to ground through trigger may be broken or disconnected.

This system appears to have Magnetic Triggers - Is this coil a dual in one pack container ??

www.britishbikebits.com

KIT00052 Boyer MKIV Ignition Kit - 12v Twins BSA, Triumph - BBB

Boyer Bransden MKIV Ignition Kit - 12v Twins BSA, Triumph
www.britishbikebits.com www.britishbikebits.com
Click to expand...
Hi Laverda SF2
Yes it is a pointless ignition system, i have tried both plugs plus a new one all work on right side, but not left, it is a duel one pack coil with a single wire to each of the secondary connectors.
I have tested the secondary circuit which gives 1.9 ohms, but can get no reading on the primary with and without the sparp plug caps fitted
 
Good LUCK ! If you have ignition issues on the road you can always get a point system to work; whereas, your dead in the water most times with an Electron System.

Try swapping the ground wires on the coils - That is see if each coil will fire a plug - if not I would suspect a bad coil side or bad spark plug wire. If it does fire I would suspect a bad Pick Up Trigger , Wires to and from the ECU Box or possible the Box itself.
 
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get any cheap dual outlet coil, wether it fits or not from a wrecker, (jury rig it any way you can) and try it, if one plug fires it is highly unlikley to be primary (LT) side related, and its only secondary (HT) after the coil.
CLEM
 
Hi other more clever people
Further to my earlier thread re: ignition problem.
I took the dual coil off and decided to see if I could remove the HT lead to the non sparking cylinder, well apparently they're not replacable, so thats one knacked coil.
I was considering using 2 x PVL 6 volt coils, but having googled it, I would need to install ballast resistors, and in any case, I can not see where I could mount them, as the wiring beneath the fuel tank is the most god awful mess, I've never seen so many wires and such gigantic connection blocks on a motorcycle.
Or if I replace it for another duel outlet coil, is the TEK MP08 the one to go for?
 
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Held onto my original 70 Bosch Copper strand Plug wires and Plug Shields till the very end along with the original points and Bosch Coils through a few sets of Bosch or Champion BE8 or 9's or until I was filing metal to Gap the Points - Did a little fab on a set of Echlin Blue Flame VW Beatle Points and all ended well through to 2018 when I decided, in my old age at 70, I was not fit to handle a 70 750 Breganzie SF and sold her ;o(

Who say's a 70 Breganzie 750SF can't hit 8000rpm and do 120+ mph down any straight on points and be more reliable Vs using Electronic Ignition crap that will leave stranded and Guess What - You Loose the Race.

My 70 Breganzie SF was not only most rewarding motorcycle but the most hands on motorcycle I've ever ridden - Bar None - As side from the fact she always wants to kill me.

She particularly liked long distance grueling road races (400 / 800 miles of Northern Ontario Asphalt) but not shabby in the 1/4 either - About equivalent to a Yamaha 1100 LTD for her time and pass 3 of them in the 1st corner never be seen again ;o)

WARNING ! She's Lady that demands Respect and Abeyance and teaches you to shit yourself with out crashing.

From my experience the Breganzie 750 has to be the BEST Motorcycle ever made for Enthusiasts - Mainly because, she can WIN Races and serviced on your Wife's kitchen table and teach you how to ride.

Just ask Ducati 750s, MV Augusta 750 and perhaps some of our 3 Cly Breganzie motorcycle enthusiasts in this forum ;o)

I've been riding since say 12 and my 1st road bike was a 67 650 BSA Lightning (19 years old) racing a 500 Norton Manx Single. 2 Farm Kids wanting to get to Wassaga Beach to Party on a Saturday night. We were Farm Boys driving Tractors, Combines, Manure Spreaders and not to say the less Motorcycles ;o)
 
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Sounds like it's time to rewire the bike - it's very difficult tracing elec faults when you're faced with a horrendous array of dodgy wire and connectors. If I was riding a std SF I would retain the original Bosch coils. Sure, they're bulky, but they work a treat and I never had one fail. My original SF1 40yo coil even helped me trace a faulty coil issue on my partner's ZZR Kwaka.

Failing that, it should be pretty straightfwd to trace the fault when you basically have two separate ignition systems. Just swap stuff across until you isolate the prob.
 
We tend to agree piranha ;o)

On thing about racing the Breganzie 750 "Farm Tractor" where you can easily melt a piston - I'm guilty of that on both accounts - But I'm the one that fix that piece of shit and given me a little piece in time, I would have to Tubo-Charged that sucker.

Just amazing how much power them 2 little Breganzie 750 pistons can put out well before their time - Plus I got a Yamaha 550 Twin CDI System that can virtually bolt into a 750 Breganzie Twin with minor mods, in the closet - Any One Interested - PLUS - Duel 34 Mukini VHS Carbs included .

I always wanted to it - But never did - It's hard to kill the Breganzie 750 SF before she kills you or Wife does.
 
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The biggest issues I had with my 70 Laverda Breganzie SF was the Tires and the weight of oil in the forks Vs both front an rear - Perilli did NOT make an 18" Rayon Radial Belted Tire any more ;o(

O course I blew the Engine up more then once or twice but it was the Tyre and Suspension that kept on 2 Wheels
 
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Thanks for the advice guys, next time I promise I will post my query and then wait a day before I decide to start ripping the bike to pieces, so just have to wait to get another coil, then I will follow the advice.
I didn't fit the electronic ignition or the dual coil, but I can see why they went for a single coil with dual outlet, easied to find a position to mount it.
The bike could well do with a rewire, although a lot of the wires have been replaced and all the connectors, until Saturday everything worked fine, so will just sort out the immediate problem .
May in the Northern hemisphere is not the best time to decide to start rewiring a bike, unless I don't actually want ride any bikes this summer, another 7 weeks and the days start getting shorter again, and we are still getting frosts.
 
I'm confused. How does a dual coil work on a 750 Laverda?

OK, I admit to being a bit of a dunce as far as the 750 twins are concerned (I've never owned one) but as far as I'm aware, the original setup has two points and two coils. The points cam is gear driven off the crank and rotates at half engine speed. That means it can't be a wasted spark system, even though the pistons rise and fall together.

You can't drive a dual output coil from two sets of points. The same goes for a pointless electronic ignition. An electronic system fitted to a 750 twin will normally have two pickups (as stated in the original post) and two coils. Although different configurations are possible with smart electronics.

If it really is a double output coil and wasted spark system, then it either has two lobes on the ignition rotor and one of the pickups is redundant, or the two pickup signals are somehow sorted out in the electronic box and fire the same coil. I know nothing about Boyer ignition systems (and there's bugger-all info on their website) so it could be either of those alternatives, or maybe another that hasn't occurred to me.
 
I'd kind of been thinking the same thing, Cam. Maybe the coil is a two-in-one???!!! So it processes two separate inputs through two 'halves'. Geez, I dunno ...
 
Gerald said:
copyright with author van Dijk
Click to expand...
Hi Gerald
That's exactly so.
I've ordered 2 (Its how they was listed) Tek Mp08 coils , (ex VFR) from eBay, will use the best one, and new HT leads, for now, to save me having to fabricate too complex a method of mounting, if that does not solve the problem then I will test the pick up coils.
I've just had a Sachse ignition delivered to fit to my 500, so by the time I have fitted that I will have a better understanding of the electronic ignition set up
 
Electronic ignition on SF can have two pickups and a single lobe rotor and each pickup firing it's own HT coil. In this system the plug leads must be on the correct side for TDC compression. Alternatively it can have a twin lobe rotor and one pickup that fires both sides at once - a wasted spark system - and both plugs fire every time the pistons pass TDC (as per the Ignitech I have on my street SF2, and the Sachse system I recently fitted to a friends bike). I am having trouble understanding why Boyer would have two pickups and a twin plug coil. With only two wires to the pickup plate it would seem to be a single pickup system but I have never seen one so maybe they have some weird electrickery in that black box. It will be interesting to see if a new coil fixes this bike.
A 500 Laverda has 180 degree crank and has to have two pickup system with two coils.
 
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