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NSF18B2 Compression Test

I

Inshore22

Member
Planning to do a compression test on an NSF18B2 with electric start. I've watched a lot of videos and read some forum posts and it seems like the steps are:

1. make sure battery is fully charged
2. run the motor till its warm and then run gas out
3. pull off the kill switch lanyard
4. remove both spark plugs
5. put compression tester into spark plug hole
6. press electric start button and get reading on compression tester
7. repeat 5 and 6 for other spark plug hole

Is this correct?

Also, I'm not clear on whether I need to do something with the spark plug wires. I've read a lot of stuff about sparks jumping and damaging wiring and don't want that to happen.
 
That should be fine. Remember that that motor has starting decompression, so at RPMs below say 500, your readings will seem low. Expect maybe 71 psi. At RPMs around 1000, the decompressor disengages, and you get full compression, about 135 psi. You can also remove the EX rocker to get full compression for testing, but then you will need to reset valve lash after testing.

Plug wires are no issue. No wiring will get damaged.
 
I did the process above with the only addition that I opened the throttle to WOT per the compression tester instructions. Got right about 147 on both cylinders. Is that okay?
 
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