I’m trying to perform a compression test as described in service manual for my MT-01. But, the starter motor is not able to crank the motor sufficiently when the decompression solenoid is disconnected.

The battery is in good shape.
But I don’t know the condition of the bearings within the starter motor. Should the starter motor manage to crank the motor with a resistance of around 12 kg?
I just got a thought. I only removed one spark plug from one cylinder. Maybe it should be less resistance for the starter motor if I remove a spark plug from the other cylinder too?

The reason why I’m performing a test is that I think I felt a power loss last season.

I appreciate any useful information that helps me perform a successful compression test.


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  This might seem rather obvious but you cant get an accurate compression measurement if you remove the spark plugs...!!

Yes, I know that’s obvious. I think I was a little bit unclear in my description. I measure one cylinder at a time and for that cylinder I replace one spark plug with the manometer. But, removing a spark plug from the other cylinder doesn’t affect the test but hopefully it makes it easier for the starter motor. Anyway, I have tried that but it didn’t work either. So, I got a tip from a friend to perform a leak down test instead of a compression test. I have looked at some videos at YouTube. Maybe I buy a tool for that instead.


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You need to make sure the crankshaft doesn't suddenly turn when air pressure is applied. Then you can listen in the inlet, exhaust and crankcase ventilation for where it hisses the most. 20% loss is said to be normal btw the gauges.
But another thing comes to mind, how old is your battery? An old, power consuming battery can make even a powerful engine seem sluggish. Happened to my car (285 hp) last week, I thought something was wrong. Then the battery failed altogether and I installed a new. The car was again its old self.
I will buy a new battery for the MT for this season.