Compression Test

Still having issues getting the Sporty to start. She turns over, sounds like she wants to go… but nope. Have tried a fresh battery and some starter fluid with no luck. Couple of buddies on Facebook said I may not have good compression. So time to try a compression test.

I picked up a compression tester on Amazon for under 25 bucks.

I probably could have borrowed/rented one from the auto parts store but figured it could come in handy in the future so I added it to my toolbox.

Service manual says I should have at least 120 PSI compression on each cylinder with the motor warmed up and both cylinders should be pretty close to the same. Well she won’t start, so can’t warm her up. Just going to see if we get anywhere close.

Removed both spark plugs and grounded them. Hooked the compression tester on the front cylinder and turned the motor over with the starter a couple times.

Getting close to 190 PSI on the front cylinder.

Repeated the same test on the rear cylinder.

Pretty close to the same result on the rear cylinder, ~190 PSI.

Compression seems to be fine. I am at a loss. Seem to be getting spark, fuel, and compression. She should run 🙁

Going to take a look at the timing now. Maybe it is just so far off that it will not go. I am also may tear down the carb again. Already cleaned it up and rebuilt it, but just going to double check things to make sure nothing is clogged up. Would think if it was the carb she would hit on the starter fluid. Anyway time for some more tinkering.

Here is a good video on how to run the compression test.

1 thought on “Compression Test

  1. i am having the same issue as u on the nightster 1200 08. fuel? check. spark? check. air? check. compression? check 180-190 front and rear. what did u doi to get ur sportie to run after the compression check/

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