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buttro63

I Would Like To Do A Compression Test On My 1995 XP150 Motor. What Is The Normal Reading And What Would Be The Lowest. Also Is There Any Electrical I Should Undo Before I Do The Test So I Do Not Short Anything Out

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kevimchale
Do test full throttle - no choke. Should be around 120 psi or more but more importantly should be within 10% of each other.

Electrical will be hurt if you crank it without putting a spark plug in each spark plug wire and shorting the plugs body to ground.  A pair of jumper cables work well for this.

Perhaps pulling the safety lanyard will disable the spark but still allow the engine to turn over which would be the best way to prevent electrical damage.
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buttro63

should i take all the plugs out?

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kevimchale
Likely best to do 1 at a time.  It will be spitting fuel out of every spark plug hole which could be ignited from a spark plug or at least causing a mess.
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amackhrandilal
Best Practice Tip
Compression test reveals how well, or poorly, an engine's piston rings and valves are sealing the combustion chamber. Consult the engine's service manual to find out exactly what an engine's compression should be. Generally, it's about 150 pounds per cylinder.
To run this test, remove all of the spark plugs and fully open the throttle. With the engine warm, crank the engine through two or three revolutions.
Read the compression gauge and record its highest reading. Repeat this procedure for each cylinder. Cylinder compression is considered acceptable when registering no less than 80 percent of the manufacturer's specifications.
The difference between each cylinder should be no more than 12 to 14 pounds.
 
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