Compression test? Proper way to test...

[dart451]

Working on a DR brush mower with a Briggs 8.75 hp 120502-0116-B1. Seems a bit sluggish when I engage the mowing blade. What is the proper way to check compression on most Briggs engines? On first pull I get 45 lbs, 2nd, about 65 lbs, and 3rd 90 pounds. Just wondering if a valve adjustment might be in sight before I take the valve cover off. Thanks.

[creia]

The very FIRST thing- The throttle MUST opened completely! (if you do not your readings will be way off). Then pull 5 times in rapid succession. The reading on your last pull is your compression PSI.
Michael

[bgsengine]

The very FIRST thing- The throttle MUST opened completely! (if you do not your readings will be way off).

Right

Then pull 5 times in rapid succession. The reading on your last pull is your compression PSI.
Michael

No actually pull until the needle stops moving. whether it be 5 times or 20

[creia]

The very FIRST thing- The throttle MUST opened completely! (if you do not your readings will be way off).

Right

Then pull 5 times in rapid succession. The reading on your last pull is your compression PSI.
Michael

No actually pull until the needle stops moving. whether it be 5 times or 20

You are correct, however, on the 50+ engines that we have compressioned-tested over the years, I have never seen the needle climb any higher after the 5th pull.
Michael

[KE4AVB]

120Q502-0116-B1

If sluggish I would also be checking spindle and Idler pulley bearings.

[RoyM]

A compression test really is not an accurate indicator of engine condition because of the automatic compression release. A leak down test is more accurate and can pinpoint problem areas. Check your valve clearances, if they are off performance will suffer.