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Goodo

SPARK PLUGS?

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Hi all.

sherpa 250 , how come I’ve seen some of them with 2 spark plugs in the head?????

cheers

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One for the start, one for running the engine,
That was common back then, so a hotter plug to start with and a colder for running, but this was more related to racing engines.

 

Back then you often had decomressors, (I btw. like them very much), and when these units failed with the time (where not tight anymore) most people mounted a second plug instead to mount a new one as it is not so easy anymore to get the right ones, (I dno't mention the chainsaw decompressor units instead these with cables and Hand Lever).

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Thanks very much for the info.was wondering why.im sure I’d seen it on another Bultaco but not the Sherpa.

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Hang on a sec.i can only recall seeing ONE spark plug lead!!!!!looking for the pic now

Edited by Goodo

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Double ignition is also possible and some still think that it will do something to the better,
and you still can get double ignition systems from VAPE in Czech for example.

A double iginition and plug for wone cylinder would make sense with big bore engines,
and there are some big V8 and V2 engines with nearly 1l cpacity in one cylinder,

But with the Bultaco you don't have that big diamater bore so you will not have any surplus
power, what you can archive is a longerr working ignition if the engine is running on the rich
side just to survive and not seizing.
Two stroke engines running much castor oil and super high rpm are prune to kill their plugs,
as plugs don't like too rich mixture and fail easily then, with a double plug you can archive a
longer life time in racing, so if one plug is failing the bike will still get a spark. 

Bultaco Pursangs come into my mind, too Pursangs being used for Super Moto and Bultaco
Street Racer.

 

Edited by pschrauber
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2 hours ago, pschrauber said:

One for the start, one for running the engine,
That was common back then, so a hotter plug to start with and a colder for running, but this was more related to racing engines.

Interesting I have never heard this.

My TSS has 2 plugs and a decompressor, The second plug fires 1/64th of a degree after the top plug the theory being with an oil rich mixture it is to ensure an efficient burn.

it was a concept introduced by Alfa Romeo for their Grand Prix cars       

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Often if both plugs actually fired it was because the head design was not the best.

My CZ race bike ran twin plugs standard, only 1 was connected to the points & the second plug fired just after. Combustion chamber is a trench at the back of the cylinder on both 250 & open class machines

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Well I’m new to all this,trying to follow what ever I is saying lol.

so why would a bike have 2 plugs but only 1 connected? Fins broken and someone just replaced it with what they could get?

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Thanks for all the answers chaps.may be me being thick but I’m still non the wiser lol

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Twin plugs but with one lead? Thats either what pschrauber says, a decompressor hole plugged with a plug, or so whenever you oil the plug, you can swap your plug lead to the other plug. And because the second plug was at a distance from the ignition point, it will not have oiled.

Edited by faussy

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 The plugs would foul easily, so you could just change the lead. Not having to change a hot plug.

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