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My 445 has a miss. I replaced the plugs. No help. Compression on the left cyl is 125# the right is 105#. If I pull off the coil wires one at a time the engine slows so I think they are both firing. The lawn tractor sat over the winter with a tank full of ethonal free gas with sea foam.
 

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Your cylinders have a 20 psi difference, that could be a problem on these engines. Was that test wet or dry for those readings? If dry do a wet ( add some oil via the spark plug hole) and report back. Hopefully a 445 owner with a TM and CTM will be able to look up the compression values.
 

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My 445 has a miss. I replaced the plugs. No help. Compression on the left cyl is 125# the right is 105#. If I pull off the coil wires one at a time the engine slows so I think they are both firing. The lawn tractor sat over the winter with a tank full of ethonal free gas with sea foam.
Coils are where I would start.

How long did you run the engine? Sometimes, even with sea foam and ethanol free gas, it could be a fuel system issue which might clear itself with some fuel system cleaner.

I wouldn't dive too deep before ruling out the simple stuff first...........
 

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When was the intake/exhaust valves adjustments done? Manual states every 300 hours.

Found the TM1517 from 99

Specs: 170 PSI minimum with no more than 14 PSI difference between cylinders maximum

Cold engine valve adjustment is 0.25 mm (0.010 in) both intake/exhaust with no sign of valves sticking

So I would check your valves if these have not been done. Or get it done by a dealer or small engine mechanic

Carbon build-up is keeping things from seating properly most likely.
 

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Here is the information from the Technical Service Manual for testing the Ignition coils. It shows the test locations and the procedures, Using an Ohm Meter,

Tractor in neutral

Key in Off Position

Remove the spark plug wire from the tip of the spark plug

Disconnect the two electrical wires from the end of the ignition coil (Wider wire is positive, Narrow Wire is Negative)

1. Using an Ohm Meter, Measure the resistance between the positive wire on the end of the coil (wider wire A) and the Negative Terminal (narrow B) lead on on the end of the coil. Note the resistance amount.

2. Measure Secondary Coil Resistance between the Positive Terminal on the end of the coil (wider wire A) and the spark plug connection wire which goes onto the tip of the spark plug (shown as C) . Note the resistance amount.

3. Remove coating from core at meter probe test point. Measure core insulation resistance between positive terminal (wider wire A ) and coil core itself which is D in the illustration. Also measure the resistance between spark plug wire (c) and core (shown as D). Note the resistance amount.


Acceptable Results
Primary coil resistance should be 3.4 - 4.6 ohms

Secondary coil resistance should be 10.4 - 15.5 k- ohms

Core Insulation resistance = infinite (no continuity)

If the values do not meet these specifications, replace the ignition coil
 

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Assuming the test is done correctly, with the engine warmed up, the air cleaner clean, the valves properly adjusted, etc,

The MINIMUM Compression Number is 170 psi and the maximum acceptable difference between the cylinders is 14 psi.

If the tractor ran fine when you put it away and now it has a miss, I would focus on the simple things first, such as Electrical Connections, Ignition Coils, Fuel system conditions, etc. before diving into a major repair.

If the tractor had not been running correctly when you put it away or stopped using it last fall, then you may want to focus on other issues once you have ruled out the basics.

This is incredibly simple, but make sure the air cleaner and assembly doesn't have a mouse nest built in it blocking the air flow. Over the winter, this is very common.....check all components carefully and don't assume they are clear.
 
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