New tractor new issue

I have a tractor that was running great for the last five years, it had a total rebuild, pistons, sleeves, rings and the whole works or so I ve been told. Recently it s developed a miss, the first thing I checked was compression, #1 was at 110 lbs, #2 was 135lbs #3 was 140 and #4 was 150 anyhow, with that being said, there is no smoke, spark plugs look perfect.. it just has an pronounced miss. I went back and added oil to the #1 cylinder and then took another compression check, it went from 110 to 155 with oil added. Anyhow, even tho no I knew this, trudged on. The tractor would die under a load erratically. I figured it was a fuel issue, it was.. I put a new fuel line, sediment bowl was missing the screen on stand pipe and carb was missing screen at elbow. All that fixed it runs and doesn t die, but still has that stupid miss. I replaced cap, rotor, wires and plugs. While running I pulled number one plug wire off and it did drop a little.. but not like the rest of the wires did when I pulled them. Also it has petronix ignition, whoever put the new ignition on had to cut the dust cover the magnet seems to stick up to high on distributor shaft. The shaft has no wobble. The carb has been cleaned, air breather totally cleaned. All connections have been cleaned as well. I even put a brand new 12 volt coil on it for good measure. I m thinking it s a valve issue, I m going to investigate that this week. Also will check timing as well. Any other suggestions? Sorry this is so long winded..

Leak at the intake manifold?

(quoted from post at 20:19:09 07/23/22) Leak at the intake manifold?

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While it was running I pulled the choke to see if the engine would pick up or die.. it died. Even at half choke it bogged and nearly died. That should tell if it has a vacuum leak.

Maybe adjust the valves.

(quoted from post at 07:16:51 07/24/22)
Maybe adjust the valves.

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Yes that s the next thing I m going to do. So one last question, has anyone here had to cut the dust cover to make room for the magnet on the petronix ignition?

A broken valve spring will give you these symptoms . The valve will still work, but badly, allowing compression to escape and causing the miss . It doesn't explain he increase in compression after adding oil though .

Adding oil to the cylinder brought it up, so that is an indication of compression ring problems.

A cylinder low on compression will be more noticeable at idle.

The question is, why is the compression low? Could be stuck or broken rings. If you went in and fixed it now, it may clean up with new rings and a hone job.

Or run it as is with a plan to do a resleeve when the time comes.

(quoted from post at 04:31:27 07/25/22) Adding oil to the cylinder brought it up, so that is an indication of compression ring problems.

A cylinder low on compression will be more noticeable at idle.

The question is, why is the compression low? Could be stuck or broken rings. If you went in and fixed it now, it may clean up with new rings and a hone job.

Or run it as is with a plan to do a resleeve when the time comes.

Click to expand...

I m going to work on it some this week and will report back. I also noticed when o went over to my parents house this afternoon that the carb is rusting severely on the outside. We were listening to it run and I noticed tons of condensation around the intake manifold and top of carb. It was muggy and hot. I doubt that has anything to do with the miss.. but might be worth noting. I plan on taking gas tank off and valve cover off this week and checking valve clearance hoping I find one either too tight or too loose, either way I ll be focusing on that number one cylinder.. but will check them all.

Exterior condensation in humid weather and frost in colder temperatures are normal phenomena for carburetors. Evaporative
cooling due to the change of phase of the gasoline (liquid to vapor) takes heat from the air and reduces the temperature of
the air in the carb throat. Also the increased velocity through the throat reduces the static temperature. Under some
conditions, carburetor icing can occur. Not much you can do to prevent these cooling effects except to add heat. Since a lot
of these engines use a combined intake/exhaust manifold, the intake air will eventually be warmed by heat transfer from the
exhaust part t0 the intake part. In the sixties and seventies, many auto manufacturers used a vacuum powered valve to duct
carb air around the exhaust manifold to preheat the intake air until the engine warmed up. The valve was controlled by a
coolant temperature sensor. As the engine warmed, the valve switched to let cold air into the carb.
That's probably more than you wanted to know.

Had similar problems few years ago with my MF-135
Z-145 it intermittently lost compression on cyl 2
it was a sticking valve I put 2 stroke oil in the gas
for 2 tanks in order to lubricate the valve stems
problem dissapeared.

HTH Bart