40 HP Mariner - could it be the power pack?

[UNCC Grad]

My 1989 Mariner 40 HP is giving me some trouble. I did a compression check and they are 125, 125, 126, and 121 psi, so that seems to be fine. It starts and idles fine, but seems to be missing b/c it doesn't run as smoothly as it should at WOT. It seems to be a constant missing in the firing order.<br /><br />The motor is one a 16' welded aluminum tunnel hull boat with plywood floor and will barely plane out with just myself in it. It feels as if it isn't hittin on all cylinders.<br /><br />I'm thinking it may be the power pack or coils. The bulb stays tight when after it's primed and gas is getting to the carbs. Any idea what it could be?

 

[mcginleyc]

Re: 40 HP Mariner - could it be the power pack?

Well the first thing to check is the idle and WOT timing. IF they are in spec then go to the power pack, Merc calls it the switch box. They should be stacked ontop of one another on the starboard side of the engine. you will need a multitester with a DVA (direct voltage Adapter) to test switchbox output. Get a seloc manual and it will tell you the procedure. The generic voltage output from the switchbox should be 100-300V. good luck.

 

[UNCC Grad]

Re: 40 HP Mariner - could it be the power pack?

Last night after looking at the motor again, there was a brown wire that was unplugged. This wire came from the main wiring harness on the control box and attached to what looked like the stator area. Could this have been the problem? I won't be able to test the boat in the water for a few days.<br /><br />What was this mystery brown wire? <br /><br />I'm sorry for the stupid questions, but I am new to outboards and trying to learn all I can.

 

[UNCC Grad]

Re: 40 HP Mariner - could it be the power pack?

I also need to add that the motor revs fine in neutral, it just bogs down under load. I've been told it could be the fuel pump diaphragm, crossed plug wires, the power pack, the stator, or the hub slipping on the prop.

 

[Keith Buchanan]

Re: 40 HP Mariner - could it be the power pack?

Hub slipping on prop would make the engine revs increase just like when our wives burn out the clutch on the family car, crossed plug wires....well I guess the lump wouldn't idle. What does sound very probable is the fuel pump. <br /><br />On your side of The Pond, for what you guys can pick a fuel pump kit its got to be one of your first options down this diagnostic road. You should be able to pick a kit up for as little as 11 Bucks plus postage.

 

[UNCC Grad]

Re: 40 HP Mariner - could it be the power pack?

This is an old post, but I wanted to update for anyone having the same problems. It ended up being a severly clogged exhaust port from lots of trolling by the previous owner with no decarb.

 

[phatmanmike]

Re: 40 HP Mariner - could it be the power pack?

wow, i woulda never guessed that one. thanks for the update.