Re: 1970 merc 9.8 dies when in water
Spark: Basic test is to remove the plugs one at a time, have it connected to the spark plug wire, but ground the plug against the engine block somewhere. Pull the cord and see if it sparks within it's normal gap. If you're holding the plug, be sure to hold it with a well insulated pliers and some heavy rubber gloves or you'll get shocked. I prefer to work it so it sits in place grounded somewhere. This will tell you if it's sparking but will not tell you how strong the current is. Obviously you need a shady, darkish spot to do this.<br /><br />Better test is to buy an adjustable spark tester, or make one. Search on these forums to find out how to make one. I bought one for $10 from the local Snap-on tool guy -a Thexton 404, available many online sources too. I couldn't find an adjustable one in the autoparts stores around here. The tester I'm talking about is basically a clear tube with a spark plug wire connection at one end and a grounding clip at the other. The gap inside the glass tube is adjustable. You adjust the gap to the correct length (I was told 3/8 for my '74 9.8), hook one end up to the spark plug wire, the other to ground, pull the cord and see if the spark (1) jumps the gap every time and (2) is strong, sharp, blue (vs. weak, yellow, intermittent). <br /><br />If both spark plug wires test strong, you're good to go. If not, you've got to trouble shoot backwards - wires, ignition coils, switch box, and then back to the parts in the flywheel. I've not done that, but don't believe the troubleshooting is that difficult. Parts can be cheap or expensive depending on which ones. <br /><br />Search this forum for 9.8 spark for a bunch of threads on assessing and troubleshooting ignition issues.<br /><br />If this is an older engine with uncertain history, I'd sy go ahead and do the carb. It really is cheap, easy and quick. I did mine this spring with no prior experience, using a factory manual and it was no big deal (except I broke a plastic part and had to repair it with JB Weld -later replaced when I got around to it). I recommend at a minimum a carb gasket kit ($8) and a fuel pump kit ($8). A full carb rebuild kit for your engine will likely be around $60, so you might want to see if the other things get it running well before you invest in that. You also need a gallon of carb/parts cleaner with a dipping basket ($10 - but will last you a lifetime!), a can of spray carburetor cleaner ($3) and a can of or other source of compressed air. <br />Good luck on the project
