Low compression

[kentrx1]

My project 154 has become more puzzling. Has been very weak and I found throttle cable had slipped. I fixed that and adjusted governor and it is still weak. I had checked the number 1 cylinder’s compression a few weeks ago after it had warmed up and it was in the 120 range. I did not check the others at that time because gas tank was in the way and did not have time that day to remove it.
I removed gas tank and checked all 4 cylinders and now they all check below 60. It still runs and sounds the same—-no smoking or skipping, knocking, etc. I filled cyinders with sea foam and let soak a couple of days thinking it might help sticking rings, but got no change.

My questions are:
Why did compression on cylinder 1 change? Head gasket?
Should I go ahead and pull head or is there something I am overlooking? The compression did not show to leak on compression gauge—-at least not fast.

[Slim140]

If it didn't smoke or use oil I would recheck it with a different gauge. There shouldn't be that big of a gap between the numbers.

[Eugene]

Conduct a complete engine tune up, including valve tappet clearance.

Run the engine for a while, several hours, with Seafoam in the engine oil and gas tank. Then conduct dry compression tests followed by a wet compression tests.

[kentrx1]

I did check gauge with another engine and gauge was fine.

[Eugene]

Why did compression on cylinder 1 change? Head gasket?

Not likely.

Do the full engine tune up, and the other items previously suggested.

[kentrx1]

Thanks Eugene

[mozer71]

When the throttle valve was having issues, you had higher compression. Since the tank is removed and the carb can be empty, open the throttle and choke. This way, the intake isn't sucking fuel and there isn't a vacuum. Might see a difference.

[BigBill]

Do a compression test, add sea foam to the gas tank, run it till the idle increases. Do a compression test again. You could have sticky valves. Seafoam will free up sticky valves, free up stuck rings.

Remember WOT open choke when doing a compression test. Pull out the coil wire.

[BigBill]

Every new to me tractor (used) I purchase, I change the oil/filter then fill the gas tank and add seafoam to the crankcase and gas tank. I mow with it. While I continue to run it the rpms will pick up in time. The rings are freeing up and the valve guides are being lubed. Give the engine a chance to get happy, happy.

[outdoors4evr]

A 120 - 60 is a drastic change. I would expect that your compression tester was not sealing well when you did your last test.

You mentioned that you did your first compression test with a warm engine. Did you do the second one on a cold engine?

Also, by putting sea foam in the cylinder, you have "washed" the "crud" off the cylinder walls.
If your engine used non-detergent oil, then the cylinder walls probably used to have a bit of burned fuel and oil stuck to the sides of the cylinders helping to raise the compression. Probably won't account for a 60PSI loss, but it is something that changed.