cylinder #6 not firing


mike209
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cylinder #6 not firing

Post by mike209 »

looks like I need your help guys on this one.
I am finishing restoration on '79 cbx I brought home in january (in several boxes:)
engine is rebuilt, all seals, bearings, pistons, valves... are new
carbs rebuild, stock setup, oldschoolcarbs kit, Mike Nixon's booklet
engine starts but does not run on all cylinders, #6 exhaust is cold, with or without choke,
I did following tests to eliminate obvious stuff:
swapped spark plugs, same cylinder dead, strong spark on all cylinders
swapped coils, same cylinder dead
checked plug cables and spark caps resistance, all good (all new)
spark plug on #6 has no signs of action other than being wet.
Last thing that comes to my mind is problem with fuel delivery, any ideas?
carbs look good where they are now and I don't want to pull them off until I am sure they are causing the problem.

tevan
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Re: cylinder #6 not firing

Post by tevan »

I presume you checked spark with plug unscrewed and grounded good with alligator clips good. I would then check with known good plug from another cylinder. If all is no spark then maybe spark plug wire.

mike209
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Re: cylinder #6 not firing

Post by mike209 »

I checked plugs by touching them to valve cover bolt, spark is just as good as on other cylinders, I moved plug from cyl#1 to cyl#6, cyl#6 still dead, then i checked two other plugs, one brand new, one from another cbx, all plugs have good strong spark, as for plug wire, I swapped that too, every time it is the same cylinder.

tevan
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Re: cylinder #6 not firing

Post by tevan »

Just for grins change voltage wire.. The ones that are numbered 123 at the coils. It won't run swapping these but it will eliminate some things. Check spark once you get it changed again.

steve murdoch icoa #5322
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Re: cylinder #6 not firing

Post by steve murdoch icoa #5322 »

Is the compression good for cylinder #6 after the rebuild?
Are you sure the #6 plug is wet with fuel and not just moisture? #6 bowl is full?

mike209
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Re: cylinder #6 not firing

Post by mike209 »

Compression is good, fuel or moisture? Not sure now, and there is fuel in #6 bowl

tevan
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Re: cylinder #6 not firing

Post by tevan »

You still need spark for that cylinder to light

daves79x
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Re: cylinder #6 not firing

Post by daves79x »

Your idle circuit is plugged on #6, very likely. Carbs need to come off, but if you are adventurous you can get #6 bowl off with the carbs on the bike and try to work a wire up into the idle jet. If you didn't extract the pressed-in #35 idle jets during your rebuild, then you really need to - no shortcuts. You have likely read here that it takes a newbie at least three removals to get the carbs right, you have two to go. Not a criticism, just fact. These are very complex carbs and rack and require a lot of experience to get them right.

Dave

tevan
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Re: cylinder #6 not firing

Post by tevan »

I guess I didn't read your post right. Do you have good spark on #6??? If you do then I agree carb issue.

mike209
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Re: cylinder #6 not firing

Post by mike209 »

If you didn't extract the pressed-in #35 idle jets during your rebuild, then you really need to - no shortcuts
Pressed-in jets were extracted and cleaned properly, no shortcuts taken. It is only my second set of carbs rebuild, so maybe I have to pull them off the bike two more times :lol:

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NobleHops
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Re: cylinder #6 not firing

Post by NobleHops »

Yes, I'm puzzled too - do you have spark at 6?

If you do then maybe it's time to repeat your compression check on 6, see if a valve is stuck open.
Nils Menten
Tucson, Arizona, USA '80 CBX, sort-of restored :-)

mike209
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Re: cylinder #6 not firing

Post by mike209 »

Yes, I have spark at #6, sorry if my english is not clear enough, not my first language

daves79x
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Re: cylinder #6 not firing

Post by daves79x »

Yes, Mike clearly said he had spark on #6 early on - that's why I'm focused on the carbs. That's where the problem is.

Dave

tevan
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Re: cylinder #6 not firing

Post by tevan »

Ok. My bad. Carbs is the answer..

mike209
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Re: cylinder #6 not firing

Post by mike209 »

Update:
I started engine with exhaust off, cyl#5 and#6 not firing, I pulled carbs and took apart #4,5 and 6, found some crap in #4 slow jet, carb #5 and 6 nice and clean. Could carb#4 affect other two? This is getting confusing.

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