Experienced gardeners share their insights in answering this question :
Hi and welcome to FixYa, I am Kelly.
This is a symptom of a dirty valve seat or poor valve seating. The valves need to be hand lapped with both corase and fine grinding compound. The intake valve is stciking silightly open. A compresson test would prove this.
There are two 20 Hp engines for the1045. The single cylinder and the V-Twin
The service manual for the single cylinder is here:
From page 97 of the manual:

Lapping Valves (Note the vavle sprin must be dis-connected)
Reground or new valves must be lapped in, to provide
a good seal. Use a hand valve grinder with suction
cup for final lapping. Lightly coat valve face with fine
grade of grinding compound, then rotate valve on seat
with grinder. Continue grinding until smooth surface
is obtained on seat and on valve face. Thoroughly
clean cylinder head in soap and hot water to remove
all traces of grinding compound. After drying cylinder
head, apply a light coating of engine oil to prevent
Note: ALL valve grinding compound must be washed off as it is abrasive and will damage the cylinder wall, piston and rings if not properly cleaned.

The service manual for the V-Twin is here:
From section 9 of the manual:
Hard starting, or loss of power accompanied by high fuel consumption, may be symptoms of faulty valves. Although these symptoms could also be attributed to worn rings, remove and check the valves first. After removal, clean the valve heads, faces, and stems with a power wire brush. Then, carefully inspect each valve for defects such as warped head, excessive corrosion, or worn stem end. Replace valves found to be in bad condition. A normal valve and valves in bad condition are shown in the accompanying illustrations. (See manual section 9)

I really think that correcting a valve problem will correct your issue.

Thanks for choosing FixYa,

How to Identify and Fix Common Gardening Problems ?

We provide a variety of viewpoints on how to identify and fix common gardening problems. Our sources include academic articles, blog posts, and personal essays from experienced gardeners :

Why would the engine only run while the choke is on or with repeated manual priming? An engine that requires the choking (partial or full) after initial engine warm up is an indication that the engine fuel air mixture system is out of adjustment.
If your lawn mower begins to backfire and does not start, it is most likely due to a faulty fuel system. It`s possible that the gas is old and has gone bad, or that there is water in the tank. In either case, you`ll need to drain and replace the fuel in the gas tank.
Why do I sometimes hear a loud backfire noise when I shut off my engine? Backfire, or more accurately “after fire” when it occurs when stopping an engine, is caused by unburned fuel/air mixture being ignited by the heat of the muffler.
Why Does Your Lawn Mower Only Run With Choke On? Your lawn mower only runs with choke on because of a problem with the engine fuel-air mixture system, which can be caused by the carburetor, bad fuel, or air leaks. The choke compels more fuel in the combustion chamber to help the engine to turn over when cold.
When does the bike run only with a choke? This mainly happens when there is dirt in and around the parts of the carburetor. The areas of concern here include fuel lines, petcock, pilot jets, or fuel filters. The dirt blocks the fuel passage and it cannot reach the carburetor properly.
If your bike is only running with the choke on, it`s probably because it`s running too lean. This can be caused by a few different things: All internal combustion engines need three things to run: fuel, air, and spark. If any of these are missing or not working properly, the engine won`t run.

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If the clutch will not engage it can be that the cable is not regulated to pull the clutch enough this is an idea on a real car.


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