cylinder not firing, then OK

hypnohio
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cylinder not firing, then OK

14 Jun 2011 12:55

Having an issue with my '82 KZ440. when I start it cold, #1 cylinder is not firing or is barely firing.I give it some throttle, and after a few seconds it comes alive and then everything is fine. Idles great, runs great. Anyone have this situation or know what it might be? I'm getting ready to run through the ignition system but thought someone might know what can cause this. Thanks.

1982 KZ440 LTD
2003 EN500 C
2006 Virago 250

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apbling
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Re: cylinder not firing, then OK

14 Jun 2011 13:08

#457234

I have similar issues with my 750-4. #1 doesn't fire when choked. Runs fine and dandy otherwise. Carbs are spotless, so I have no clue what the deal is. Once you crack the choke to about 3/4 from full it starts to fire. Reproduceable all day long.

Anyway, your situation... Have you checked valve clearances, inspected coils/wires/plugs? maybe your pilot circuit is dirty or someone tinkered with it? Have you balanced/synched your carbs at all?

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bountyhunter
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Re: cylinder not firing, then OK

14 Jun 2011 15:16

#457263

Pretty much has to be caruburetion. The spark plugs on twins are wired in series so an electrical failure that keeps one from firing would take them both out.

1979 KZ-750 Twin

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martin_csr
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Re: -

14 Jun 2011 16:15 - 14 Feb 2013 11:23

#457265

.

1981 KZ650 Competition Sports and Road

Last edit: 14 Feb 2013 11:23 by martin_csr.

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hypnohio
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Re: cylinder not firing, then OK

14 Jun 2011 16:24

#457266

put on new plug wires and caps and cleaned all the connections I could find -same deal.

1982 KZ440 LTD
2003 EN500 C
2006 Virago 250

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hypnohio
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Re: cylinder not firing, then OK

14 Jun 2011 16:30

#457267

apbling wrote: I have similar issues with my 750-4. #1 doesn't fire when choked. Runs fine and dandy otherwise. Carbs are spotless, so I have no clue what the deal is. Once you crack the choke to about 3/4 from full it starts to fire. Reproduceable all day long.

I'm glad to hear someone else is experiencing this - your description fits perfectly, especially cracking the choke to about 3/4. Carbs are synched, valves are set, and new wires and caps on the plugs made no difference. Since it's running fine otherwise it's not a life or death issue, but really has me stumped.

1982 KZ440 LTD
2003 EN500 C
2006 Virago 250

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MFolks
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Re: cylinder not firing, then OK

14 Jun 2011 17:06

#457268

Tried a different brand of sparkplug? I've had no trust in NGK's after having many fail right out of the box. I'm using Denso's now with no problems.

1982 GPZ1100 B2
General Dynamics/Convair 1983-1993
GLCM BGM-109 Tomahawk, AGM-129A Advanced Cruise Missile (ACM)

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hypnohio
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Re: cylinder not firing, then OK

14 Jun 2011 17:39

#457272

I'll give that a try. At this point anything is possible. Thanks for the suggestion.

1982 KZ440 LTD
2003 EN500 C
2006 Virago 250

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bountyhunter
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Re: cylinder not firing, then OK

14 Jun 2011 19:11 - 14 Jun 2011 19:13

#457285

martin_csr wrote: The problem could be the spark plug wire connections which become poor from oxidation over time.

Almost impossible. The spark plugs on a twin are in series across the HV winding of the coil secondary. The current to make either plug spark passes through both plugs. Only way to get a single plug firing is to short across the other plug's gap or short one plug wire to ground. An open wire, fouled plug, etc will cause both plugs to not fire because they are in series.

Learned this the hard way when my 750 twin was fouling the left plug and would strand me. Even though the right plug was fine, zero spark at either plug.

1979 KZ-750 Twin

Last edit: 14 Jun 2011 19:13 by bountyhunter.

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