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[ChrisD]

Hi Guys. I took my newly rebuilt 1996 535cc Enfield on a 5-day ~1500km ride last week (after 500kms trouble-free testing). The engine went well but the coil slowly died over the trip – misfiring a bit, then getting worse and allowing only 1/4 throttle then much of the time missing then death! This is the twin-plugged 8.5:1 compression bike and the coil was our hosts dual lead coil (EMGO). Some of you indicated (notably TimNZ) that coil should not be used for a twin-plugged bike, and I now concur!

SO: I need a pair of 6v coils, but I note that the Boyer Brandsen twin electronic setup (Hitchcocks PN 92004), advertised as suitable for a twin-plugged 500 Bullet, is barely GBP90 more than the cost of two coils – and it includes the coils. So why not? I would also loose the points which are forever advancing too fast (despite the shortened springs and the reduced weights) giving pinking.
Can anyone who has made this change give advice?

Many thanks, ChrisD

[Bullet Whisperer]

Hi Chris, Twin plugs will not make any noticeable difference. If you have pinking [with correct ignition timing], try retarding the inlet cam by 1 tooth, it will lower the cylinder pressure on the compression stroke and also boost power and revs, while losing nothing much low down. Regards, Paul.

[ChrisD]

Thanks BW. Yes, I am aware of that. But the twin plugging, metal-to-metal head joint, high cap oil pumps etc were solely to reduce heat at the exhaust valve. Riding recently in the Karoo desert at around 40degC - nothing else removes heat enough. Already retarded inlet (timed using dial gauge too).

The advance curve is a guesstimate from weights ground down to ~10grm, springs of near double tension but still, 80kph up hill into a strong wind at ~1000m above sealevel means the bike always pinks unless I go down a gear. I need a proper advance curve – preferably one that is easily tunable for different conditions.

Cheers, ChrisD

[vince]

Hi,1. I had coil go like that, it was traced to regulator over charging. 2. Try fitting an oil cooler in the return line to the rockers. I made one from an old fridge radiator. I a bit confused about you comment 'advancing to fast'. Vince

[Adrian]

Chris,



I don't know if this will help or if it's available in SA, but Kal-Gard Gun Cote might be an idea. I'm assuming that you're already running an alloy barrel. Scroll down here:



http://tedsshed.co.uk/paintwork-3/engine-coatings/

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[Tim NZ]

The EMGO coil should have had the correct resistance to suit which ever ignnition system you were running: EI OR Points? The coils a re not interchangeable between systems...


Check the specs of the coil to confirm suitability.


Otherwise, sounds like it could be that your condencer that has died?

[stinkwheel]

It was my understanding that "twin lead" coils actually produced one spark that goes up one HT lead then down the other? Or maybe I imagined that? I'm not certain it's in any way relevant.



I was always told you should set your static ignition timing on a low powered bike with the cam locked in the fully advanced position on the basis that a bullet will be spending most of its time there anyway. The ignition retardation is just a way to get it to start and idle without biting you.

[ChrisD]

Gentlemen.

It has been noted that the OEM A-R curve for the 1996 500 Bullet is too steep – reaching full advance by ~1500rpm – so I wanted to delay that as LesH suggested by lightening the weights and strengthening the springs. Also I prefer to kickstart with only 6-8 degrees of advance since I have twin plugs and a 8.5:1 piston – so in order to get 28-30 degrees of advance, I need an A-R curve that reaches perhaps 24degrees, i.e. longer than normal. Yes, I know that maybe I only need 28degrees of advance for normal usage, but, as some of you have also stated, a higher advance may benefit at higher revs as noted by Ace Café and Adrian for the AVL. And since I have fitted a steel conrod, roller bearings, lightened valve gear etc I wish to use those revs, since I have paid for them! See the attached advance curve data.

With the A-R curve at max by ~2500-3000 rpm, the engine is not over-advanced at lower revs, such as going up a hill on a road where slowing below 50mph is dangerous (i.e. a freeway).

Regarding the coil, there are so many conflicting stories. But notwithstanding the advice from Mr H, the dual output coil is NOT suitable for a twin-plugged single, especially if the compression is higher than OEM.

Tim-NZ – yes, condensor is OK (tested new and older ones). Yes and I followed your advice for the improved cooling effect by fitting twin-plugs.>br>
And Paul, I recollect your note in 2009 that your racing 350/500’s are twin plugged and removing a plug cap sees the power drop off by up to ~10% (yes, probably only at revs I can’t reach). But still, any power drop is a lot for most Bullets!

Thanks Vince – I shall check the regulator next. Also the oil cooler issue – but there are many out there who say that too is unnecessary although I doubt many of those naysayers have tried riding the bike at temps well over 40degreeC through a poorly inhabited semi-desert). So I shall continue investigating that.

Adrian – thanks for the advice but since I have a beautiful alloy barrel, why paint it? Besides, there would always be someone out there who’d tell me how wrong that was as well.

Stinkwheel – the dual coil is a “double-ended” one - yes that’s my understanding too.



SO: is there anyone out there who has fitted a Boyer to a twin-plugged single (RE or other) and can they provide advice on it?

Thanks, ChrisD (hope the image shows up!)

[Bullet Whisperer]

Chris - you misquote me!! I disconnected one plug of the two on the 500 racer when it was on the dyno and it lost 0.2 bhp from 42 - hardly 10 percent - and the 350 racer runs only one plug, does 9,500 rpm, wins races and is the 2018 BHR pre '63 champion ONE PLUG IS ENOUGH for any Bullet !!! Regards, Paul.

[Adrian]

I think the twin-plugging thing for classics originally started with worries about unleaded fuel. Some of the lore being bandied around at the time was that the ignition timing should be retarded by 5° with twin plugs. I had been working on a twin-plugged BSA Victor project at the time, and had I ever got it near being finished, following that advice would have meant a full advance figure of 23° BTDC, which seems way too retarded. From Bullet Whisperer's comments it sounds like I needn't have bothered! A good stable ignition and a properly set-up carb would have done.

From the look of that Pazon advance curves chart, the brown one for the early 1971 BSA B50 seems to be of most interest. The B50 was/is a high-comp twin valve 500 single from the heady days when you could buy 5 Star petrol, same 84x90 bore and stroke as an un-modded 500 Bullet and (for 1971) same ignition timing at 32° BTDC on full advance, according to the chart. Pazon and Boyer are different companies, so they may have different philosophies on what makes a good advance curve, but as Pazon was founded by ex-Boyer employees it might be similar.



http://www.pazon.com/pages.php?pageid=10&mode=preview



Cosmetically speaking I have to agree with you that bare alloy top ends LOOK better, especially when you consider the powder coating that RE India currently insists on plastering over the UCE heads and barrels. I'm guessing that's a general-purpose coating to minimise corrosion rather than a specialist treatment. That said, if I were regularly running a Bullet in desert temperatures and I knew that Gun-Kote actually did what it said on the tin, I'd be sorely tempted, never mind what "someone out there" might think.



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