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Zed Head

All brains on deck - an unusual problem

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Has anyone ever seen two adjacent cylinders, on two different carbs, foul in an identical manner and in the same amount of time?  While leaving the others clean (except for one that's half dirty)?  It's an odd thing that might mean something to someone.  It's from the poor-idle-when-hot problems on our Panama member's 204Z with ZTherapy SU's.  

This picture, apparently, comes from six brand new plugs installed, engine started and allowed to run for ten minutes, then plugs pulled.  Is there anything carb intake system related that could cause fuel-fouling like this?  Has anyone seen such a dramatic difference between cylinders like that?  So clean, next to so dirty, all in ten minutes.  If it was EFI we'd have all kinds of ideas.

Here's the picture, the currently active link, and a drawing from carpartsmanual for reference.  Just a new look at an old problem.

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https://www.classiczcars.com/forums/topic/60072-misfiring-while-cruising/?page=7&tab=comments#comment-558478

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Weird. No, I don't have an obvious answer, but here's some musings.

There's no guarantee that all three cylinders fed from the same intake manifold get exactly exactly the same percentage of input stream, but they've got to be close enough to not result in that. All those Z's on the road running carbs with the stock intake... I'm no expert, but I've not heard a contingent of people complaining that the intake manifolds were designed such that 3 and 4 run twice as rich as the rest.

Those clean plugs don't look like they've got anything at all on them. Like they're still brand new out of the box.  After ten minutes or so idling, I would expect to see something on all of the plugs. I can't see anything in the pic... Is there at least something on all of them?  Maybe the root problem is with the clean plugs, not the dirty ones?

I would confirm that all the cylinders are firing (probably by pulling spark plug wires while the engine is running or some other potentially dangerous method). Pull and ground each plug wire in turn and verify that the idle RPM goes down and gets rough? Don't get zapped, and don't burn out your ignition system by running OC.

I would also check the valve lash and run a compression test. Make a note not only of the final peak compression pressure, but also make note of (about) how many compression cycles it took to reach that pressure for each cylinder. If four cylinders take three revolutions to get to peak, but the other two take ten cycles, that could be a clue.

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What about disabling each carb, let it run at idle and see what the plugs look like?

I can't stop thinking those two aren't getting fire like the rest. Maybe try a spark test in the dark or low light on each one? 

That petronix system is something I know nothing about so I'm throwing stuff out there.  Alabama game is boring. LOL

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I've never used one of those flashing spark checkers, the kind that fit between the plug and the wire.  Has anyone used one of those?  Would a misfire show up in the flashing even though it's fast?  Don't know if the human eye could catch it.

Here'a thought that just came to mind.  One of those old engine analyzers.  That would show misfires, if I recall right.  They might still be around down in Panama.  That would be a quick easy way to show if spark is good or bad on all six at the same time.  If I was down in Panama I'd try to find a shop with one of these I think.  Might make things clear pretty quickly.

http://www.enginebuildermag.com/2015/10/old-gold-vintage-engine-analyzers-and-distributor-testers/

 

 

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 Speaking of old engine analyzers, my Dad used to check his plug wires by waiting until dark and spraying water (spray bottle) on the plug wires while the engine was idling. It was my first of many light shows to come. @jalexquijano Give it a try. You never know, it might turn something up.

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Is it possible the coolant line between the two manifolds could be the culprit?  That's the only thing that connects the two from what little I know. The spacers have more holes on the later 240s too. That slimy octopus is falling pretty quick off the wall now. LOL

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I have another wild arse guess, based on an old memory about the Pertronix trigger ring and the tape holding it on.  I believe that the magnetic ring is actually six magnets isn't it?  Or it's six bits of iron that pass a magnetic sensor.  Not sure which.

In the past, Jalex noted that the tape was peeling off of his, if I recall right.  If the trigger ring slipped, could this give two bad triggers out of six?  Do the bits inside the ring move separately?

I've never had a Pertronix igntion system so don't know all of the fine details about how they work.  But it might explain why the plug wires and plugs and cap all look good but there still seems to be some misfires.  Each magnet or iron piece triggers a certain cylinder.  Another reason to use an analyzer, I think, then work backwards to find the cause.

In the meantime maybe take a good close at how the Pertronix parts are fitting under the cap.

Edit - it's magnets.  Hall effect is the term I couldn't remember.

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Edited by Zed Head

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regarding the color tune (clear plug). Have used one, you can slow down the video and really see what is going on.

 

 

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power testing idea is 1st thing to check. pull one plug at a time, and see effect on idle. Please video while doing so we can all get a good chuckle and the zapping received. Or get some of those long purpose designed pullers that lets you grab the plug cable at the spark plug and pull with out the risk of getting zapped.

The problem with trying to diagnose over the internet is you always miss some crucial piece of the puzzle that the OP is just not relaying. The power test is the most obvious starting point, and perhaps it has been done, but if it was you would think there would be a huge imbalance just by looking at those plugs. what is thought to be loping due to a cam could really be loping due to a complete misfire. I have seen cars that sound like crap and the owner thinks its supposed to sound that way. So agree with capt O, I suspect the problem is not with the black plugs but the super clean ones not firing at all. the black is a result of trying to compensate for 4 others that are not working at all.

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29 minutes ago, Dave WM said:

the black is a result of trying to compensate for 4 others that are not working at all.

He has carbs though.  What would the "compensation" be?  The air-fuel mix happens at the carb and should be essentially the same for each of the three runners being supplied. 

The other side of the view would be "how can an engine run on two (or three) cylinders.  Assuming the clean ones are "dead" and the dirty ones live.  He said that those plugs were actually in the engine but there's no way to confirm.  Hopefully he wasn't just putting new plugs in the picture for comparison.

One reason we've focused on ignition is, like you said, internet diagnosis is difficult.  If we could confirm that spark is good for all six then we could ignore spark and focus on fuel-air, or oil, or compression, or valve timing, etc.

The power balance check is a good idea except for the fact that he has electronic ignition.  And ignition modules tend to be sensitive to having nowhere for their spark to go.  He might fry his Pertronix module, as CO implied in his comment.

 

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1 hour ago, madkaw said:

Blown head gasket? 

I thought it might be bad valve seals myself.  But folks are fairly convinced that the fouling is fuel fouling.  My old 76 engines with worn valve seals had all six plugs pretty dirty, but not wet though.

He says that all six cylinders give a solid 180 psi pressure reading.

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I'm not trying to crush ideas, just reviewing past discussions with Jalex and others.  The simplest solution would be to find a mechanic who knows engine basics but they seem hard to find down there.  Any good mechanic would look at those six plugs, if they are actually new and came out like that, and have some ideas. 

The picture of all six plugs fresh from the engine is new info.  Seems much clearer than any of the past discussions about Far311 cams, and percolation, and poor idle.

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2 minutes ago, Patcon said:

Someone got, the firing order off the top of your head?

That's a good one.  1-5-3-6-2-4 is correct.  Maybe he some wires switched.  That fits bad spark.

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3 minutes ago, Zed Head said:

That's a good one.  1-5-3-6-2-4 is correct.  Maybe he some wires switched.  That fits bad spark.

I was mainly working off your theory on bad pickups. I was hoping 3 and 4 were adjacent, suggesting a damaged section. However they are exactly opposed...

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21 minutes ago, Zed Head said:

I thought it might be bad valve seals myself.  But folks are fairly convinced that the fouling is fuel fouling.  My old 76 engines with worn valve seals had all six plugs pretty dirty, but not wet though.

He says that all six cylinders give a solid 180 psi pressure reading.

You can still have good compression with a blown HG. Might be enough coolant to foul plugs but not to cause a smoke. Need a pressure checker to find it 

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could feed up some solid copper up the boot, exposed wire could then be grounded to kill the spark. I can't imagine it NOT having a power balance problem though. from the look of those plugs I would think it would idle terribly.

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Are those NGK's? Doubt if it's the problem but they have a tip that screws on where the plug wire connects. They can get loose. I remember someone said they can misfire if they get loose. I always tighten mine up a bit (using finger-muscle not pliers) when installing plugs.

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I think if he had a wire swapped it would run more poorly than it does

What he really needs is a substitute dizzy. That would eliminate the pertronix as an issue

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What he really needs is a competent mechanic, as he does not posses and has not learned  the skills himself!

There have been so many issues with this car the owner could , by now, have paid a Z specialist an all expenses paid vacation to Panama for a month to work on the car and he would  come out $$$$$ ahead.

Especially if you make any accounting at all for aggravation.

My trusted mechanic, Jose, is from Honduras and cut his automotive teeth as a child learning firsthand from his grandfather and dad what it took to keep cars and tractors running dependably and indefinitely. They were extremely poor by U.S. standards and there was no running off to the dealer or parts shop for anything but the most vital of components. They ingeniously made do with what was on hand. I am constantly amazed at Jose's ability to read complex technical information in ENGLISH and comprehend what needs to be done, step by step, to effect a proper repair. He does not assume, jump to conclusions, or deviate from his methodical approach. Mechanical devices don't run on  "maybe", hope,  and wishful thinking.

The Moderators have my permission to flag this rant as "Not Constructive".

 

 

 

 

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4 hours ago, Zup said:

What he really needs is a competent mechanic, as he does not posses and has not learned  the skills himself!

 

 

 

 

I totally agree.  There's no shame in not knowing how to fix everything on the car you drive.  There are many older cars and trucks in Panama and someone is keeping them on the road.  Jalex should ask around (friends, relatives, coworkers) to find a mechanic who knows how to work on an older car with a carburetor.  Not sure if he ever tried to connect to a local car club, as suggested, for support.  The mechanics he has used most recently have not helped.

Dennis

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