You should check the valve lash first, especially on that low cylinder.
Your carb may have had some debris stuck in the air bleeds or in the main wells, and the high vacuum under closed throttle engine deceleration may have pulled it out of there.
BUT......
as to that low cylinder, I am more inclined to think;
your compression test points to the valves not sealing on it.
>If the fault lies in the exhaust valve, firstly;on the intake stroke the falling piston will pull some high-pressure exhaust gasses into the cylinder, along with some fresh mixture from the intake. If the exhaust is hot enough, or still burning from an adjacent cylinder, then this inducted mixture can ignite as the piston is coming up, and the expanding gasses would attempt to force the piston back down. This energy is now subtracted from the energy going into the crank from the previous pulse of another cylinder, and so you feel it as a "miss". You can prove this by removing #2 ignition wire, and the engine smoothes out a little.
Secondly,when the fire gets lit under compression, some of the burning gasses will exit into the exhaust manifold, still burning. If there is a combustible mixture in there from another or other cylinders, and say oxygen also got in there from an exhaust leak, well you could have a bit of a pressure spike in the log every time that bad cylinder fires, which might altogether sound and feel like a missfire.
> If the fault lies in the intake valve, after the intake stroke finishes, and now on the compression stroke; hot intake charge will sneak back into the intake manifold, making the left over mixture,on ignition, a weak pulse and you feel the crank slow down. The pulse that went back into the intake will mess up the carb.But the worst is; still-burning,high-pressure, exhaust gasses could find there way into the intake manifold,igniting the fuel charge just expelled into there. When that high pressure pulse hits the carb on it's way to the atmosphere, it will draw fuel with it because the venturi doesn't care which way the air is moving thru it, to dump fuel into that stream. So now you have a mixture of hot exhaust gasses and an enriched charge sitting in the filter house, getting ready to be pulled in by the following 5 cylinders. Is it any wonder the engine doesn't want to idle?
>But suppose that intake valve just had a small piece of carbon stuck between it and the seat, and the valve spring just couldn't crush it. And suppose /6-64 comes along and stabs the throttle a few times and blasts it outta there; suddenly all the monkey business, or most of it, stops, and the engine gets back to business almost as usual.
This is a very likely scenario that has probably been going on since the beginning of the internal combustion age. It used to be more common before EFI. Crappy gas, crappy oils, and crappy engines of yesteryear would combine in a tired engine, and the recipe was ripe.Many years ago we used to take our cars out for a high-speed run, every so often, to clean the carbon out. ( I told a cop that one time, but I got the ticket anyway)
So what to do about it?
Well the first thing I would do is a LeakDown test to prove that this is what's happening and to prove which valve exactly it is. Then I would pull the valve cover and put the involved piston at TDC-compression and check/record the valve lash. If both valves have more than zero lash, then I would make a cursory check of the valve springs to make sure none is broken, and that there is at least some seat-pressure.
Then I would back up the crank to pull that piston back down on the compression stroke at least a half an inch or more. Then I would bop that bad valve about 866 times with the butt-end of a hammer and listen for a change in the sound it makes, when the valve hits the seat.To speed this up,I do this at TDC with the LD tester injecting air; then it becomes obvious if the bopping is working, as the hissing stops simultaneously with a new sound as the valve slams into the seat.I have to warn you tho, that the piston is right there so you have to kindof know what you are doing so you don't slam the valve into it and bend her....... cuz then you are for sure gonna need a valve job.
OK so after the valve is again seating, you do a new valve lash test, and an adjustment if required. And then since the cover is off, you might as well do the rest. And repeat the LD test to note the change, and a new compression test on that cylinder if you are so inclined.
No not 866 times !! lol, if the sound never changes, and the LD test shows little if any improvement, then we are too late the valve is burned, and the valve-job is the only known cure. Usually a half dozen bops will prove it one way or another.
> There is a shortcut that sometimes works, and that is a chemical dose thru the carb at a fast idle. You can find these products at your jobber.
Good luck
i just dont understand how it was not able to idle then started to idle again.
