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Snapper LT125 with Briggs 23Hp Model 44L777 V-Twin. The cylinder on the brake side valve cover is much hotter to the touch than the other side. It runs fine but does exhibit some popping when the engine is shut off unless it is throttled to an idle first. Why would one valve cover be hotter than the other?

History: This mower was scrapped and I bought it for $30 from the scrapper this winter. It was dirty but in great shape. After cleaning and a good battery it would only start with starting fluid. When the brake was released it shut off. To make a long story short, this is what I found.

The battery was installed with a green wire leading to the brake switch under it breaking the wire. When repaired the tractor drove when the brake was released.

At some point the carb was removed and reinstalled incorrectly with the throttle and choke linkage placed in the wrong holes. When the choke was set the throttle plate was actually wide open.

When the shroud was removed, both cylinder heads had two of the largest mice nests around them that I have ever found. About a gallon freezer bag of nest material was removed.

Last, on the hot cylinder side, the valve cover had been removed and reinstalled with the incorrect bolts, stripping three of the threads in the cylinder head and the valve cover gasket leaking badly. Before installing a new gasket I tried to re-tap the three bad threads. Two were successful but the lower right bolt hole cracked in the cylinder head breaking the hole out on one side. I was able to install a bolt with a washer and nut hoping it holds. This valve cover has the vacuum line going to the fuel pump in it and a new fuel pump had already been installed.
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Why the carb was removed, why a new fuel pump, why the valve cover was removed during previous service, I do not know. However the hot cylinder is on this side. Today my grandson cut the grass for the first time. The tractor and mower ran excellent for a total of about 40 minutes. Inspecting the tractor after he was done I found the hot valve cover. I believe there is a valve issue. Am I correct? Can it be solved with a valve adjustment or is there a bad valve? How can I confirm if a valve is bad?

Poor maintenance procedures killed this tractor for the previous owner and I am picking up the pieces.

Many reasons. Are the cooling fins clean and clear? These are air cooled engines. One cylinder firing and the other not? One cyl with good valve lash, other lash incorrect? Weak spark on one side, other side good spark?

TiIngot said:

After cleaning and a good battery it would only start with starting fluid.

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Most likely dirty carb or fuel system.

TiIngot said:

When the shroud was removed, both cylinder heads had two of the largest mice nests around them that I have ever found. About a gallon freezer bag of nest material was removed.

Click to expand...

What I preach about daily on here. Clean the cooling fins yearly or you will get engine damage.

TiIngot said:

Last, on the hot cylinder side, the valve cover had been removed and reinstalled with the incorrect bolts, stripping three of the threads in the cylinder head and the valve cover gasket leaking badly. Before installing a new gasket I tried to re-tap the three bad threads. Two were successful but the lower right bolt hole cracked in the cylinder head breaking the hole out on one side. I was able to install a bolt with a washer and nut hoping it holds. This valve cover has the vacuum line going to the fuel pump in it and a new fuel pump had already been installed.
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Nice job.

Pull the engine cover again. Pressure wash the block, heads and cooling fins. Get all around each cylinder clean as in new engine looking clean. Dry with compressed air or leaf blower.

Verify spark on each cylinder.

Verify each cylinder/exhaust pipe gets hot as normal.

Open valve covers. Verify each valve moves into the head the same distance as the adjacent valve.

when you pull the valve covers compare coloration of the oil deposits. It the valve spring is blackened noticeably on the hot side you may have some exhaust gases escaping thru the exhaust side. Also make sure the muffler is open on the hot side. Mud wasps and critters like to plug them up. Considering that people have been playing with the carbs, that side may be running lean.

Kinda sounds like a blown head gasket. Leak down test should be able to rule this out or not.