carb adjustments

[gspd]

... make extra sure that you have strapped the plug threads down so they touch the fins...and there's no possibility that they will vibrate/loosen.

Strapping it down is very a good idea if you're running the engine. Glad you mentioned that Kurt.

If you have plastic or rubber after-market spark plug caps, assure that the actual spark plug threads or body are touching the fins.
if you have metal OE type spark plug caps, just the outer shell touching the fins is OK. It's the same thing electrically as if the actual spark plug threads or body are touching.

I've blown coils and automotive electronic boxes (a hunnert years ago) by unknowingly attempting a simple compression test with the wires hanging. Kind of embarrassing (and costly)

[pdx_r100s]

so as I looked into doing this shorting approach, I discovered that my coils aren't set up with the lower plugs going to one coil and the upper plugs to the other. Each coil connects to a lower plug and an upper plug on the opposite side. I forget where I got the diagram for setting it up, but I used something that I found online in a discussion for dual plugging. I also think that this is how the other electronic ignition was wired when I got the bike (it had a dyna on it).

so disabling the coil won't work, right?

[gspd]

so disabling the coil won't work, right?

If killing the spark to either cylinder is too complicated, just kill the fuel supply instead.

[Rob Frankham]

On essence, plug shorting on a bike with electronic ignition isn't a good idea.

+1
Hi Rob, glad you're back, hope you're feeling better.

Experienced mechanics have figured out how to avoid getting zapped when playing with ignition systems.
I learned my lessons from experience, which is not always the best way.
I've had my share of 'zaps' over my lifetime and I'm still completely norbal.
When properly done there is absolutely no danger, but it's hard to explain the exact do's and don'ts here.
That's why I suggested that pdxr100s just lay a spare spark plug on the engine; this assures no zapping or possible component damage.

I'd be interested in hearing your opinions and personal experiences concerning dual plugging.
Also, your views on using one coil for the 2 left plugs and one coil for the 2 right plugs? (as opposed to the conventional one coil for the upper plugs and one coil for the lower plugs setups). The only advantage I see with the conventional setup is that it will allow the bike to keep running perfectly for decades if one coil fails, so much so that you'll never even know it has failed. However, the other way, at least you'll know for sure right away when one of your coils fails. (but that failure could cause you to lose the race or be late getting home)

Hi,

Yes thanks, neither my partner or me had a particularly bad time with the lurgy... it did take some time to completely get over it though. Pretty much back to (ab)normal now. Yes getting 'zapped' is pretty much an occupational hazzard and I would agree that it is not necessarily going to kill you but the possibility remains that it can. You can get a shock a thousand times and walk away and then on time 1001, the circumstances will be wrong... you might be holding on to bare metal with the other hand, you might be kneeling in a damp patch or you might just jerk and hit your head... the only thing is , if you're really unlucky, there won't be a time 1002. It's right that people should be aware and avoid a shock if at all possible. Any way, enough of Jonah mode,

I have never dual plugged an airhead so any opinion I have is based on first principles and hearsay. Nevertheless never let it be said that I would avoid offering an opinion (informed or not) if asked .

Advantages... It seems to be generally accepted that the combustion chambers on 247 series engines are not particularly good. The plug of to one side and the thin combustion chamber (according to better minds than mine) slow down flame spread and inhibit the production of energy. This being the case, a second spark is very likely to lead to better combustion and more efficient use of fuel leading to better performance, fuel consumption and emmissions... PROVIDED... that the engine is properly tuned following the conversion. Simply sticking dual plugged heads onto a stock motor and expecting it to become a rocket ain't gone happen. That being said, there is no consistent evidence to quantify the improvement and it could well, in the real world, be very slight. I'm very sceptical of completely subjective claims of improvement from any aftermarket mod. Yes, dual plugged bikes might run very well... but so do most single plugged bikes...

Disadvantages -

Complication - no more need be said...

Physical vulnerability... the bottom plugs are vulnerable to physical damage and to degradation from road debris and road chemicals.

Workmanship and modifictaion. The job really does need to be a skilled undertaking. The amount of metal available in the lower half of the head is quite small and this needs to be machined to allow a fitting face for the plug. The amount of metal available for the plug thread is small. If used with a 14mm plug, the thread is more likely to strip so many convertors use a 10mm or 12mm plug in the hope that this will help... which it doesn't really it just means that there is still less thread area.

Would I consider doing it? No, but that's not a helpful answer because I like my bikes pretty much as they came off the production line. I'm not the sort of owner who needs to get the last hp and the last foot/ounce of torque and my airheads perform well enough for me with single plugs. That doesn't mean that I am decrying experimentation or modificatiom... I always tend to the opinion 'it's your bike, do what you like... just don't expect me to like it be too sympathetic if it doesn't work out'.

Would I buy a bike with dual plugs? A big question and depends on a lot of other factors, let's just say it wouldn't be a plus factor in the equation.

OK, I've rambled on enough...

Best wishes and thanks for the concern.

Rob