plug gap for use with Dyna coils

  • happyhunter
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plug gap for use with Dyna coils

01 Oct 2015 16:19
#692887
I recently upgraded my KZ305 to Dyna coils. I want to take advantage of the hotter spark for easier starting in cold weather. I have heard the hotter spark can use a wider gap to give better starting. What size gap should I use? Should I change the plug type?

Thanks,
HH
'82 Kawasaki KZ305CSR
I did not set out to buy a project bike,
but I got one anyway.

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  • Patton
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Re: plug gap for use with Dyna coils

01 Oct 2015 17:39 - 01 Oct 2015 18:02
#692894
happyhunter wrote: I recently upgraded my KZ305 to Dyna coils. I want to take advantage of the hotter spark for easier starting in cold weather. I have heard the hotter spark can use a wider gap to give better starting. What size gap should I use? Should I change the plug type?

Thanks,
HH

Would use the factory recommended spark plugs and the factory recommended plug gap.

Look for fat blue sparks (not thin orange sparks) on removed plugs -- otherwise attached and grounded -- while cranking the engine. Fat blue spark is evidence of a healthy ignition.

Even with fat blue spark, difficult cold weather starting may result from such causes as imperfect carburetion and/or insufficient compression.

Is the stock airbox in place?

What are the spark plug readings?

New spark plug wires? With solid metal core?

Good Fortune! :)
1973 Z1
KZ900 LTD
Last edit: 01 Oct 2015 18:02 by Patton.

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  • Rustyhama
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Re: Re:plug gap for use with Dyna coils

02 Oct 2015 01:43 - 02 Oct 2015 01:45
#692920
I'm no expert in this area but I do have a 305. I mostly ride 10 minutes to work & back every day and I used to suffer from fouling plugs. I've recently found that running hotter plugs has given me a much more consistent performance, (and I have her tuned pretty sweet now) . I have never played with the gap. I have also replaced my coils with some kind of generic replacement and they seem to help too.

So, to answer your question if you do short journeys like me then consider hotter plugs otherwise just keep em stock, including gaps.
Hama

'82 KZ305-B1 Cafe Racer
'80 Z750E project
www.dotheton.com/forum/index.php?topic=59260.0
Last edit: 02 Oct 2015 01:45 by Rustyhama.

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  • bountyhunter
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Re: plug gap for use with Dyna coils

02 Oct 2015 15:36
#693070
I know a lot of internet press says to widen the gaps on plugs with "hotter" coils but I have never seen a single bit of data (real data like dyno or speed testing) to show it does ANYTHING. Here is the myth: since it's true that a weak spark can cause poor fuel burn and loss of power, it MUST be true that a bigger/hotter/fatter/whatever spark must mean you will get MORE power. It just isn't true. If you have sufficient spark for good burn, more doesn't do anything.

What is true: the coil is a flyback transformer that stores energy in it while the points (or switch) is closed. When they open it dumps the energy through the spark. The gap doesn't change the total energy stored on each cycle. HOWEVER: the voltage across the coil winding builds up to whatever voltage is needed to force the spark to jump the air gap so it can spark. Widening the gap increases the voltage stress on the coil on every spark and shortens it's life proportionately.
1979 KZ-750 Twin

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  • KZB2 650
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Re: plug gap for use with Dyna coils

03 Oct 2015 10:51
#693150
bountyhunter wrote: I know a lot of internet press says to widen the gaps on plugs with "hotter" coils but I have never seen a single bit of data (real data like dyno or speed testing) to show it does ANYTHING. Here is the myth: since it's true that a weak spark can cause poor fuel burn and loss of power, it MUST be true that a bigger/hotter/fatter/whatever spark must mean you will get MORE power. It just isn't true. If you have sufficient spark for good burn, more doesn't do anything.

What is true: the coil is a flyback transformer that stores energy in it while the points (or switch) is closed. When they open it dumps the energy through the spark. The gap doesn't change the total energy stored on each cycle. HOWEVER: the voltage across the coil winding builds up to whatever voltage is needed to force the spark to jump the air gap so it can spark. Widening the gap increases the voltage stress on the coil on every spark and shortens it's life proportionately.

I remember reading this in a bike magazine (many years ago) where they recommended .037 with Dyna coils and I did it for a while...... but like you said never seen much more on it being a proven hop up so I went back to and stayed at .032. At the same time they recommended the thin wire plugs of the time (forget what they were) gold tips, Platinum ? ? Iridium wasn't out yet.
1978 KZ650 b-2
700cc Wiseco kit 10 to 1.
1980 KZ750 cam, ape springs, stock clutch/ Barnett springs.
Vance and Hines Header w/ comp baffle and Ape pods, Dyna S and green coils, copper wires.
29MM smooth bores W/ 17.5 pilots, 0-6s and 117.5 main
16/42 gearing X ring chain and alum rear JT sprocket.

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  • daveo
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Re: plug gap for use with Dyna coils

04 Oct 2015 10:45
#693292
Patton wrote:
happyhunter wrote: I recently upgraded my KZ305 to Dyna coils. I want to take advantage of the hotter spark for easier starting in cold weather. I have heard the hotter spark can use a wider gap to give better starting. What size gap should I use? Should I change the plug type?

Thanks,
HH

Would use the factory recommended spark plugs and the factory recommended plug gap.

Look for fat blue sparks (not thin orange sparks) on removed plugs -- otherwise attached and grounded -- while cranking the engine. Fat blue spark is evidence of a healthy ignition.

Even with fat blue spark, difficult cold weather starting may result from such causes as imperfect carburetion and/or insufficient compression.

Is the stock airbox in place?

What are the spark plug readings?

New spark plug wires? With solid metal core?

Good Fortune! :)

Definitely "New spark plug wires, with solid metal core", and non-resistor caps! Then you can experiment with "R" plug types.
Since changing my caps from resistor, I'm in a whole different world now...where I'll stay for awhile. B)
1982 KZ1100-A2

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