Re: how to properly check timing on 97 merc 5.7
Howdy,
You just need a "regular" timing light. but I would also start with another known gage to verify that you really are overheating...
If it's a 97 it's probably a Thunderbolt V ignition system?
It will have to be put in "BASE" mode before you check the timing.
You set the timing at idle rpm 10* BTDC while in the base mode. The service manual indicates how to put it in base mode.
Here's the specs.
http://www.boatfix.com/merc/Techbk/techcov.pdf
There should be a wire hanging off your distributor. It's PUR/WHT in color. It may have a little rubber or plastic plug in the end to insulate the connector when not being used.
You ground it which places the ignition into "Base Timing Mode" Then set the timing the "normal" way. You can also adjust the carb idle mixture and idle rpm too.
Don't forget to lift the wire from ground after you're done.
The service manual outlines the procedure. Evidently that service manual is not on Boatfix. If you don't have one it would be a good investment if you're planning to do your own work or you want to know what's going on when someone else does it.
Now having said all that, timing is not frequently the cause of overheats in a boat engine. You might want to check the raw pump, and raw water system for debris from a previous raw water pump disintegration or other source and the pump itself for problems. Also check for good water thru the manifolds/risers, thermostat, and circ pump etc.
Maybe you checked all that stuff...
Cheers,
Rick
