Merc 9.8 Issues

[atimm693]

I've been having some issues with my outboard.

I bought it not running and it was missing a diaphragm in the fuel pump. Installed that and it ran pretty good, but would act up sometimes. While moving at wide open throttle it will begin to drop speed and eventually stall of you don't close the throttle. It would do it once or twice and it normally was fine for the rest of the trip.

Last week it acted up worse than ever. It ran fine on the way out, but on the way back wouldn't run at all much above idle. It will run all day at low speed, but falls on its face when you throttle up.

After that I went through the carb yet again, found no issues. A couple wires on the switch box were rotten so I replaced those, and I also replaced the fuel line and primer.

I thought I had the problem licked, it ran perfect for 30 minutes or more, took it 3 miles from the ramp to fish some bridge pilings,

I fished for an hour or so, started up and left, about 5 minutes in on the return trip and started acting up yet again. Same deal, 1/8 throttle only. Took me 40 minutes to make it back, but it ran the whole way. Pumping the primer did not help.

I have taken the line off of the carb and pumped the primer. There is lots of fuel flow there. The carb is spotless. When it's not acting up, it runs perfectly.

Any ideas? It's really starting to get frustrating.

The carb kit came with two diaphragms, one rubber and one plastic. I installed the rubber one, was that the right choice?

 

[ondarvr]

Have you checked for spark when it's acting up?

 

[atimm693]

I haven't that may be something to try the next time I have it out. Although it doesn't seem like an ignition issue to me.

 

[60sboater]

Try the other (brown) diaphragm. There's been a lot of discussion about which on another site.

 

[atimm693]

I pulled the plugs and the top plug was noticeably damper and cleaner than the bottom plug. Maybe it is losing spark.

I will swap the diaphragms as well and see what that does.

 

[60sboater]

The "sometimes" issue does seem more like electrical/ignition. You could swap wires (to see if the problem follows) although 1's wire may be too short to reach the bottom plug.

 

[atimm693]

I checked the primary side of both coils for resistance and they were very close to each other.

I also put my meter across the wires for each coil and got very different readings. Maybe that is part of the problem.

This motor is a 79 and has the Type III Thunderbolt ignition according to the Seloc manual, with two ignition coils and a switch box.

If anyone has some pointers on how to test the components in the ignition system, I'm all ears.

 

[hardwater fisherman]

Take a look at the cdi electronics website. A lot of good info there. I am not sure if your motor is covered there but take a look at there trouble shooting guide.

 

[atimm693]

The CDI book was a great read, and did cover my model. I checked the stator while running and voltage seemed pretty steady.

With it running in a barrel I sprayed some carb cleaner in the carb whenever it started to die and it would take off again, so it was starving for fuel.

I swapped the brown diaphragm in as well, the old one was just slightly tattered on one of the check valve flaps. It's running well now, so we'll see what it does on the lake tonight.