Looking at a 2014 z7 in a couple days but all the shops are booked for weeks. This will be my first boat. Anybody familiar with performing a compression test on the Merc 150 Pro XS or similar? Gonna have to do it myself and I'm told Mercs aren't really straight forward in regards to the compression testing process. TIA!
Pretty easy.
1. hook up muff and warm motor up.
2. remove all spark plugs
3. pull kill switch. Important step. If you forget this you can get the crap knocked out of you by a spark and the coils do NOT like forming enough voltage to make a spark and then the spark having no place to go. It can/will find a weak place in the coil housing and burn through it and cause a short, costing you a new coil or two (or six). You can always ground all the plug wires, but if one comes loose, theres a zap or blown coil waiting to happen. Kill switch solves that.
4. throttle-only button and go to WOT
5. cylinder by cylinder screw in the compression gauge, and spin motor at least 2-3 times, or until the gauge stabilizes. Repeat.
6. replace the plugs, reset the kill switch, pull throttle back to idle.
The most common error is forgetting to move throttle to WOT (you can hold the butterfly wide open on the port side of the motor if you prefer, but throttle only is easier). If you forget WOT, compression readings will all end up low since the motor will be starving for air to compress.
There's a FAQ here in the mercury motor section that goes thru this as well.
2008 Bass Cat Pantera Classic
2014 Mercury Pro XS 200
This is according to Don Weed @ European motors. He's is the best around for Mercury outboards.
Any additional info on that motor, go to the Mercury motor forum.
When performing compression tests, it's imperitive that the tests be done with:
-A fully charged and PROPERLY RATED cranking battery
-Engine warmed up to Operating Temperature
-Kill switch OFF
-All Spark Plugs Removed
-Plug wires on Spark Tester (or grounded with jumper leads- an added precaution)
-Throttle plate at the WOT Position
-Water supplied to the engine while cranking!
Insert compression tester into #1 spark plug opening, and crank the engine until the reading no longer rises. Record reading. DO NOT spin/crank for longer than 10 seconds at a time.
Repeat above step for each cylinder.
How do you turn the motor over with the kill switch pulled? Maybe I am missing something here, but mine will not turn over when in this state....
I'm getting ready to sell my boat, so I thought I would ask... Don't mean to hijack this thread...
Layton Strong
Nitro State Team
Kill switch is wired wrong, should only kill the ignition. Engine should turn over, but will not start.
Bryan McDonough
2023 Nitro Z21 XL
Nitro Team
Check if it's in neutral. In neutral, it should turn over with kill switch off. Or as BCMD said, maybe wired wrong.
Ok, I'll double check this....
Layton Strong
Nitro State Team
Probably the neutral safety switch. As I mentioned, press the throttle-only button in the center of the shift lever (near the bottom). Then you can adjust throttle while leaving boat in neutral. And then it should turn over normally. If you just go to WOT it is not going to turn over due to the neutral safety switch in the throttle assembly.
2008 Bass Cat Pantera Classic
2014 Mercury Pro XS 200
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