Dead cylinder help

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Thomas Sottile
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Re: Dead cylinder help

#16 Post by Thomas Sottile »

Jeff Adams told me he was not using Bosch plugs any more he has had many problems with misfire

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Jonathan Halpern
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Re: Dead cylinder help

#17 Post by Jonathan Halpern »

Hmmm... can it be that simple? I will check as soon as I get back to the garage. These are recent Bosch Plugs. Thinking back a little, I had lost this same cylinder intermittently over a few days last year. Cleaned out the carb and all seemed well again. Could have been coincidence and a intermittent plug was at fault. Okay, feeling hopeful. If that doesn’t work, valve check and compression test next. Rotor and cap “appear” perfect. Will swap wire as well.

Jonathan

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Ron LaDow
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Re: Dead cylinder help

#18 Post by Ron LaDow »

"While I have that pesky #3 out, I’ll see if it sparks to the chassis."

Put another plug in the hole while you test it. You do NOT want to do a spark test with one cylinder pumping the fuel/air mixture out of the empty plug hole.
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Jonathan Halpern
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Re: Dead cylinder help

#19 Post by Jonathan Halpern »

Yes, of course Ron, but thanks for pointing it out as I have seen some very silly/dangerous repair attempts! You just never know what someone knows or doesn’t know. Much appreciated.

Jonathan

Geoff Fleming
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Re: Dead cylinder help

#20 Post by Geoff Fleming »

Just check the length of the sparkplug, where it enters the cylinder...it has to be short or else the piston will contact it and bend the electrode up, preventing firing. Dropping a plug prior to installation can also bend the electrode so carefully examine the end to ensure a gap exists.

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Matthew Devereux
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Re: Dead cylinder help

#21 Post by Matthew Devereux »

I've had the dead cylinder problem a few times. It was always the carb.
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Jonathan Halpern
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Re: Dead cylinder help

#22 Post by Jonathan Halpern »

I finally got back to the garage. Easy test done. Spark plug is sparking, wire is good, ignition not the issue. Tried a new plug anyway, same issue, came out wet with gas. Other plugs all good.

I’m leaning towards a carb issue as well. Dormancy plus ethanol is always an issue. I took a look at the Zenith diagram and carbs always are a weakness for me. I just don’t see why one cylinder is fouling while the other is fine on a shared Zenith. Again, carbs baffle me. A clogged jet would prevent fuel from reaching the cylinder, I assume... can anything in particular cause very rich conditions on one cylinder?

Thanks again for all the tips and comments. Worst case I will backfire my way over to my neighborhood Porsche guy.

Jonathan

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Martin Benade
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Re: Dead cylinder help

#23 Post by Martin Benade »

You can look down the carburetor throat with it running about 3000 rpm and see if the fuel spray looks similar in both throats. Usually a wet plug would make me look for some ignition mystery.
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David Jones
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Re: Dead cylinder help

#24 Post by David Jones »

Jonathan, you could swap carbs side to side and do not worry about the linkage, just see if it will run at idle and if the problem transfers.
If I had known I would live this long I would have pushed the envelope a little harder.
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Jonathan Halpern
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Re: Dead cylinder help

#25 Post by Jonathan Halpern »

Thanks Martin and David. I will start by looking at the fuel spray and next swap the carb from side to side. That will have to wait for when my wife isn’t looking over my shoulder and at her watch.😀

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Ron LaDow
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Re: Dead cylinder help

#26 Post by Ron LaDow »

Jonathan Halpern wrote: Sat Sep 28, 2019 7:30 pm I finally got back to the garage. Easy test done. Spark plug is sparking, wire is good, ignition not the issue. Tried a new plug anyway, same issue, came out wet with gas. Other plugs all good.
If the plug is wet with gas, it's possible it is 'flooded', but more likely not firing.
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Jonathan Halpern
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Re: Dead cylinder help

#27 Post by Jonathan Halpern »

Thanks, Ron. I let it spark to the chassis and it threw a good strong spark of at least 1/2”, maybe 3/4”.
I did drive it around the parking lot and it’s backfiring through the exhaust at higher rpm only.

Jonathan

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Martin Benade
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Re: Dead cylinder help

#28 Post by Martin Benade »

You might look into lack of compression/valve clearance issues.
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Jonathan Halpern
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Re: Dead cylinder help

#29 Post by Jonathan Halpern »

Thanks, Martin. Valves are next, its on the lift now and its my next check. I’ll swap carbs if the valves are set correctly. Valve job was done 1000 miles ago and valves adjusted 100 miles ago.

Jonathan

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Ron LaDow
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Re: Dead cylinder help

#30 Post by Ron LaDow »

Jonathan Halpern wrote: Sun Sep 29, 2019 12:38 am Thanks, Ron. I let it spark to the chassis and it threw a good strong spark of at least 1/2”, maybe 3/4”.
[...]
Jonathan
I'm not sure what this means.
Did you fit a plug to the plug lead, put it on the case where it would be grounded, and test for a spark? Did you then put that plug in the cylinder?
Ron LaDow
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