dual plug head

jordan /
danjor
Jan 27, 2009 09:49AM

first i need to say that i have the highest respect for the opiniones and advise i have recieved on this fourm.

this is a two stroke that is not moped specific. i recently acuired a 75 kawasaki f11 250cc enduro. i got it running great and i will pull a weelie in first gear very easily. but i want more power. I noticed that the cylinderhead has another spark plug hole. is there an advantage to running dual plugs? also the stock compression ratio is 6.4 to1. i increased my puch 1 speed to 14 to 1 and noticed a big difference in low end torque. is there a danger in doing this whith a bigger motor. please help me im addicted to modifieing two strokes....

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Re: dual plug head

SchijnHeilig /
schijnheilig
Jan 27, 2009 12:13PM

I don't think going to 14:1 directly will be a smart thing to do. You might want to go to 11:1 or so. And if that works, gradually increase the compression. 6.4:1 is very low for an old 2-stroke, maybe your piston is worn out?

When you work the head, make sure you keep atleast 0.7 to 1mm squish (Room) between your piston and your head, to prevent the piston from hitting the head.

About the dual sparkplugs: Some people say they do work (keep the head cooler, burn cleaner) and some say it's BS. Try it for yourself.

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Re: dual plug head

 GotSpark /
couey
Jan 27, 2009 12:15PM

Is there just a plugger in the other hole now?

are both holes verticle or is one diagonally set into the head?

do you have any pictures?

I would think that running 2 plugs at once would just lead to detonation. which is bad.

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Re: dual plug head

SchijnHeilig /
schijnheilig
Jan 27, 2009 12:23PM

Dual plugs don't lead to detonation, detonation is self-combustion of fuel caused by too high temperature or pressure in the cylinder. Mostly fixable by using higher octane fuel or jetting your engine properly.

Alfa-Romeo is also very big on it's twin-spark engines, so the use of dual plugs per cylinder isn't too odd. There's even stock Puch dual-sparkplug heads, but those are rare.

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Re: dual plug head

Todd rod /
hotrodtodd
Jan 27, 2009 02:15PM

Worn out rings will not change the compression ratio. compression ratio is calculated from the difference between volume of the cylinder when piston is at bottom dead center compared to the volume of the combustion chamber. This stays constant even as the engine wears. the only thing that changes compression ratio is by changing boar, stroke or cylinder head volume. Check your compression pressure. Put a compression gauge in the plug hole and crank the motor approximatly six revolutions. that pressure reading is a good number to use. There is problably a spec in the repair manual for that motor. If you mill the head you will raise this number. You dont want super high compression pressure on a two stroke. The compression ratio of 6.4 to 1 is ok for a two stroke. If you really want more power you should get some new rings and hone the cylinder. Make sure everything is in perfect shape then clean your carb and make sure your ignition system is in perfect working order. After all that is in perfect shape you can start by changing pipes or porting. Just do your homework or you will end up with a boat ancor. Get gordon jennings two stroke tuners guide and start reading.

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Re: dual plug head

Flagrant - /
stevew
Jan 27, 2009 02:18PM

With two plugs firing the flame front for each travels less distance than for just one. A 250 might benefit but a 50cc cyl diameter is so small anyway. The faster the charge is burned the more pressure will be applied to the piston head early in the downstroke. At very high RPM this could make a difference and you would be assured when the exhaust port opens combustion would be complete w/o fire exiting the port. If 4 strokes are run too lean the flame front speed is slow enough at car RPMs that when the exhaust valve opens it gets burned by fire passing over it

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Re: dual plug head

Ian T /
iant
Jan 27, 2009 02:30PM

my '65 two stroke 80cc suzuki has 7.6:1 compression stock. I think these bikes were meant to be bulletproof.

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Re: dual plug head

Rocky M /
sickstep
Jan 27, 2009 03:49PM

Not too long ago I believe I saw a Peugeot 103 head for dual spark plugs on ebay.fr

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Re: dual plug head

human drew /
dog_poopie
Jan 27, 2009 09:18PM

2 spark plugs only work if you have 2 coils

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