procedure to check compression on xr6 150 merc

[NITRO25]

Have a 1996 merc 150 (carbs) and need to know how to check compression. After reading other post it looks like I should get 110# with no more than 10%<br />difference on other cylinders. What should I do to engine before test....warm up engine, pull all plugs and then what? Any grounding of electrical? Any help would be appreciated.

 

[12Footer]

Re: procedure to check compression on xr6 150 merc

Yes, ground the plug wires to the frame. This will keep the coils and switchbox from self-destructing. I use a set of aligator clip test leads,that come in a 10-pack at Radio Shack. They are cheap and werk great. Warm engine, no plugs in, crank engine until reading stops going-up (usually, about 4 turns or so). That's the compression. Numbers should be above 80PSI, but most importntly, equal. At least,within that 10% of each other.

 

[RHB]

Re: procedure to check compression on xr6 150 merc

Do you mean ground the high voltage secondary of the coil to ground?

 

[HowieDean]

Re: procedure to check compression on xr6 150 merc

He means the spark-plug boots... If you have a kill switch just pull it and it will ground the ignition for you... don't forget to clip it back in before you try to start it again...