Shake shake shake....

[scratchee]

It has had a lot of MMO, even a bit of WD40, in it.

Have you tried something with better penetration, like PB Blaster or an acetone/oil mix? You need something that will fight its way down along the valve stem.

[Surcouf]

...... Each of the 4 plugs made the same flashing light result. ..... I've run out of ideas.

So if I recap:
- compression in cylinder 3 OK: no valve blocked
- cylinders 1 & 2 running: so air / gas is actually mixing and getting into the manifold, AND no major back-pressure on the exhaust
- change in engine operation when you remove the plug cable on 1 & 2: so your timing should be OK
- entire new ignition system + plug tester OK on all 4 plugs+wires: all ignition system OK

Now we are really getting in the weird / difficult... So I apologize for asking it, especially as it was already mentioned before on that thread, but before you start pulling head and manifold out, I have to ask: are you 100% sure you have not mixed up cables 3 & 4 in relation to 1243 and not 1234 order? Have you tried to swap 3 & 4, just for peace of mind?
Once again, I am very humble in asking it, as it is rare to have a engine mixing air and fuel, making spark, with correct timing, no back-pressure on the exhaust, and not firing on that cylinder (exactly as you say: running out of ideas)
PS: do not ask me why I insist on that one, I got a very late night revelation when doing my overhaul, when I could not have the engine purr properly...

Good luck

[DDO]

I dropped the old points/condenser plate into the distributor and all behavior exactly the same btw. I have seen the aftmost exhaust valve up, see the stem with the camera. Still can't move it. I've checked the 1243 so many times and made others come look too -- so that will probably be it in the end, ha ha. I did not use acetone (yet). I am removing the manifold and valve cover and I'm going to stare at it all opened up for awhile. I have the new exhaust flange and pressure kit, the first part in the eventual update of the exhaust system, and a new manifold to install -- I have no idea why that appealed to me. I'll report anything interesting I find; thanks all for all the tests and suggestions.

[JOHN COOKSON]

I don't know where I'm going with this...... but anyway.

Does the #3 spark plug smell of unburned gasoline after no start cranking?
Is there a possibility of #3 intake valve being stuck closed? You'll find out when you get the valve cover removed.

ex TRUE GRIT

[Surcouf]

Is there a possibility of #3 intake valve being stuck closed? .
ex TRUE GRIT

Valve closed? interesting idea as it would explain why gas does not get in, but that would mean that either the camshaft, pusher or the valve stem is doomed

sorry for the 1234/1243, it is likely the end of it (the easiest is to swap both lines )
Good luck for dissassembly

[jbsoukup]

I apologize if someone has already covered this, but you could try swapping the #3 plug with a known good plug; maybe you got a bad one.

[DDO]

Just to follow up, I pulled apart the engine and am working to free the stuck valve, so I started a new thread "valves revealed" for that problem. I felt that I had to pull the head, manifold, and valve cover, which wasn't too difficult, to focus on that stuck valve and find a cause. So "shake shake shake" is now understood to be stuck-stuck-stuck. Thanks all for the many troubleshooting ideas.

[sastanley]

DDO..5 (or 20) years from now, someone may stumble on this thread...I recommend posting the link to your new thread so they can follow the updates.

[DDO]

Yup, I thought it a good idea to put the "valves revealed" search string instead of the link, since links all over this site broke when Moyer re-hosted and I'm a software engineer expecting that sort of thing to happen, ha ha. Link https://www.moyermarineforum.com/for...ad.php?t=11853

[sastanley]

+1 - software engineer here too. I have my 2009 newbie thread with a lot of broken links when the site was re-hosted. We do what we can..

[W2ET]

Many of the broken links can still be accessed if you change this in the post on the original host:

moyermarine.com/forums/xxxxxxx

To this:

moyermarineforum.com/forums/xxxxxx

Bill

[scratchee]

Many of the broken links can still be accessed if you change this in the post on the original host...

Sounds like a great job for a little script run on the database.