One(1) Dead Cylinder GL1200???

1079 Views 7 Replies 5 Participants Last post by Ole Guy, Sep 6, 2009

desi928s

Discussion Starter · Sep 6, 2009

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I noticed that my valves were extremely noisy and my fuel economy took a big hit...pulled valve covers and everything checked out well. Took off carbs and cleaned each one......I have fire coming from plug wire and I installed new plugs, but one cylinder is still not hitting rite. When I remove the plug wire, there is no noticible difference in the engine performance, wherein when I remove the other 3...it nearly dies Help! Missed a big ride today (a mechanic suggested a new carb/what say ye?) 1985 GL1200 Interstate

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FenderHead

· #2 · Sep 6, 2009

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Well, I wouldn't snap for a new carb without thoroughly exhausting all diagnostic tools available...have you tried a compression test?

Also, the 1200s apparently have hydraulic valves. I don't know much about them, but I'm sure that if one is malfunctioning, it could likely cause a symptom like yours. :waving:

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desi928s

Discussion Starter · #3 · Sep 6, 2009

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Thanks, will check out lifters/valves, etc.

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desi928s

Discussion Starter · #4 · Sep 6, 2009

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what should "good" compression be?

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FenderHead

· #5 · Sep 6, 2009

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desi928s wrote:

what should "good" compression be?

What I meant was a "good test", meaning - done correctly. If not done correctly, you will get false readings, leading to false diagnostics, possibly.

Your compression readings, since the bike starts & runs well, except for that one cylinder, would be considered "good" if each cylinder tested out to be within, say, 15 psi of highest to lowest readings. If the cylinder that is misfiring proves to be greatly different (lower)than the other three cylinders, it would not likely be a carb problem, unless the throttle valve isn't opening at all? Things like broken compression rings, cracked piston, blown headgasket, sticking valve would be going thru my feeble brain.

You could try swapping plugs to see if that oneplug is the problem (this has happened several times to me, even with brand new plugs).

If compression is high in the dead cylinder, there is likely a carbon buildup problem. I have also had plugs get shorted out from chunks of carbon getting wedged between the electrodes, causing "dead plugs". That has only happened to me on 2-stroke engines, however.

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peterbilt

· #6 · Sep 6, 2009

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i had the same problem on my 1100 recently it ran just fine at highway speeds, but at idle and low low speeds it had a miss on cyl 3 only i found out after testing one of the ignition coils was putting out weak spark at idle or low rpms or near idle speed but works fine at high speeds going to get a goood used coil tho.... honda's prices are outta this world

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dan filipi

· #7 · Sep 6, 2009

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Just as an fyi, pulling a plug wire on the flat four is not a good judge of a cylinder firing or not, even a strong cylinder running properly may not run any different with the wire off at idle.

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Ole Guy

· #8 · Sep 6, 2009

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Maybe it is still fuel problem. If it runs well at highway speeds, that is a good sign. It could also indicate the dead cylinder is not providing fuel at idle. It may in fact still have a clogged idle jet. So lifting the plug wire makes no difference in the idle because it is not contributing fuel when idling. Removing a good plug wire then reduces the engine to two good cylinder firing, thus it wants to die. Be sure the idle jets are clear. Also balance them. Something to consider.

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