Hitchcocks Forum

Quoting from a posting on 05th August, under Decompressor Problem: "Will a spark plug block both holes? The inner hole that vents compression into the exhaust port also needs blocking." If a spark plug will fit where the decompressor is, and a twin spark coil is wired in, does this turn the Bullet into a twin sparker! Is it that simple! Will it work! Is there any gain to be had for a standard tune Bullet! Am I barking up the right tree, or just barking...
Regards
Bullet Train

Woof woof! No, you'll not see any gain on a standard engine.

Yes it will work but no unless you plan to do other very high performance things with the engine I doubt whether there would be any real advantage. Plus of course you lose the decomp.

I can't agree with Pete or Simon. With duel plugs you'll get crisper acceleration and slightly better petrol mileage. The second plug will screw in no problem. Same threads. The down side is: You must remove the head to enlarge the hole for the decompressor so you can use a plug spanner. The decompressor hole (the small hole) must be closed permenently. You must use a plug in the same heat range BUT a SHORT reach plug. If you improuve the air filter for better flow and the exhaust for the same reason and increase the main jet one size you'll see a marked improvement. I've beening running duel ignition for the last four years and I am still pleased with it. So I know of what I speak. Cheers.

Sorry Daoud, but I have to agree with Pete and Simon, twin plugs only causes the flame front to start from two places instead of one the result is a faster burn for a split second, usually this causes the ignition to feel too far advanced and you then have to retard it slightly which almost totally removes the advantage, for any noticeable gain this is only a small part of the tuning process and on it's own not worth the trouble, on the plus side however if you get a plug failure the other one will keep the bike going.

On at least one point I agree with you Dennis. It's not worth the trouble nor the expence. For the rest I can only speak from experience which is only my perception on my bike. Have you and the others actually tried duel ignition on Bullets? Your objections seem more theoretical then hands on to me. Cheers.

Hi Daoud, Yes sorry to disappoint you but a lot of my earlier years were spent tuning Velocette singles for racing with considerable success, so I do have hands on experience of twin plugging and the benefits. ------- I am sure that you feel that your bike is greatly improved by fitting twin plugs, and there is absolutely no harm in that, after all most of us ride for pleasure nowadays and anything we think is an improvement is a bonus. ----- Ride safe and enjoy your bike.----- All the best Dennis.

I fitted twin plugs to our racing Enfields - it works well, but I disconnected one plug cap and connected it to another earthed plug outside the engine, to revert to single spark and ran it on the dyno [this was the 500]. It lost about 0.25 bhp out of 46 and the line on the readout was a little more ragged, you wouldn't really notice any difference on the road, I would think. Paul.

But Dennis, it is a good idea to have 2 plugs working but the problem is if the first plug fails you probably won't realise till the second one fails and then you will still be stopped but have 2 plugs to change

That's very true Norm, so therefore no real benefit at all on a road bike?, Hmmm, I was trying to find a positive.