Compression check.

[maverick974]

I'm having what I hope is a minor engine problem and the after checking the carbs and plugs, I want to check the compression but since the electrical systems on a Force engine are getting expensive, I'd like to make sure I do it correctly.
If I pull the plugs to do a compression check and I spin up the engine with no plugs, will that hurt anything?
Is there a way I can spin the engine without hurting the ignition? Can I just jump from the starter battery to the starter? Would that work?

Thanks.

 

[Nordin]

Re: Compression check.

Yes, you can jump the starter from battery and leave the ign.switch in OFF pos. then you do not hurt the ign.system.
If you use the keyswitch to spin the flywheel you have to ground the plugs so the CD-pack can deenergnize through the plugs.
When you check the compression, set the carbs at WOT and spin the flywheel until the needle do not move any more (about 5-10 turns on the wheel).

 

[roscoe]

Re: Compression check.

You can us the key switch if you flip the kill switch, this will ground the ignition the same way that turning the key off does.

 

[Frank Acampora]

Re: Compression check.

If your engine is pre-mercury ignition, you can jump from the battery side of the solenoid to the yellow or yellow/black start terminal with a short length of wire. Do not jump to the black terminal. This is ground. You can also jump on merc ignition but I don't remember the colors. In any case, do it with the ignition switch off and you will be OK. This keeps you from running back and forth to the front of the boat to use the switch.

Throttle does not need to be open to check compression. Since these are ported engines, the cylinder goes to atmospheric pressure every time the ports open. The engine might crank just a smidge faster with the throttle open, but it will make no difference in the final compression reading.

 

[Jiggz]

Re: Compression check.

Following Franks's instruction, you can also make a two wire (with alligator clips) with a push button switch "pigtail" (remote starter) so you don't have to connect and disconnect every time you crank the engine. They actually sell this pigtail on ebay and other auto stores. Remember you are jumpering from the source side (battery side) of the solenoid to the coil terminal (small connector of solenoid) of the solenoid.