100hp mariner starts but doesn’t keep running

[The John]

I am having a problem with my 89 mariner where is starts sputters and dies.

I used the boat two weeks ago and everything was fine, ran normal. I tried to start the motor and it tries to start but doesn’t keep running.

I checked the fuel vent and it was bad, so I replaced it thinking my troubles were over but the motor is still not running.

I would like feedback on where to start as I have some mechanical ability but my knowledge of outboards and thier operation isn’t great. I have an outboard manual (like a chilton) and all of the tools I think I would need.

Compression is good on all 4 cylinders
Fresh gas
Fuel/water separator is clear
New spark plugs (1 month ago, still in good shape)
It has oil, the oil system is functional
Fully charged battery

 

[flyingscott]

Get a factory manual , it is a must for your motor. That motor is a 2+2 motor and starts and idle on the top 2 cylinders.

 

[The John]

Get a factory manual , it is a must for your motor. That motor is a 2+2 motor and starts and idle on the top 2 cylinders.

Yes, I was hoping to get some information regarding where to start considering it was running fine a few weeks ago.

 

[Texasmark]

Remove your main engine fuel filter and cut it open....getting a replacement of course before you do that.....what's inside and how much? If black specks its fuel line degradation and you need to replace your engine's fuel lines and do a kit on the fuel pump while you are at it. Then do the carbs, complete disassembly and cleaning with solvent and lots of compressed air and little wire poked in any hole or tube you find.

If tan crystalline chunks, redo your fuel line from the fuel tank to the engine including a new squeeze bulb.

I got my used OEM service manual off ebay.

After you do that come back on here and report how it runs. We can go from there.

 

[The John]

Remove your main engine fuel filter and cut it open....getting a replacement of course before you do that.....what's inside and how much? If black specks its fuel line degradation and you need to replace your engine's fuel lines and do a kit on the fuel pump while you are at it. Then do the carbs, complete disassembly and cleaning with solvent and lots of compressed air and little wire poked in any hole or tube you find.

If tan crystalline chunks, redo your fuel line from the fuel tank to the engine including a new squeeze bulb.

I got my used OEM service manual off ebay.

After you do that come back on here and report how it runs. We can go from there.

copy that, I appreciate the advise.

I am getting a fuel pump rebuild kit today, and I have ordered a new fuel filter as well. The boat has new fuel lines but I will check the existing filter and change it out.

The manual I ordered is due this week

I will report back.

 

[The John]

Update: new fuel filter going in tonight and my buddy is coming over with a fuel pressure gage to check the fuel pump.

 

[Texasmark]

Update: new fuel filter going in tonight and my buddy is coming over with a fuel pressure gage to check the fuel pump.

Keep us posted. Fuel pressure is like a few pounds at idle and something like 12 +/- at WOT as I recall.....or maybe that's cooling water pressure I'm remembering. Bullet proof test for the fuel pump if in doubt, squeeze the bulb if in doubt.

 

[The John]

Another update, the fuel filter mounted on the outboard (I also have a water/fuel filter mounted on the main line before it goes to the outboard) was not in an operable condition (looks like the filter had collapsed blocking flow). I replaced the filter and she started and ran momentarily but sputtered. I can use the idle only throttle and it stays running at the lowest position.

My plan is to increase the idle by adjusting the idle screw for the motor (not the carbs). Does this sound like the correct approach?

 

[flyingscott]

The factory manual would tell you that.

 

[Texasmark]

On the Mercury of that HP the idle set screw is on the spark advance lever, not the carburetor control linkage. The manual states that you get in the water with the engine running, F gear, control set to idle, fast idle off, and adjust the screw (timing, white knurled knob ss spring loaded screw) until the tach reads 675 +/- 60 RPM. That speed is designed to get you shifted with the engine still running yet be slow enough to reduce "clunking" and gear wear when shifting.

 

[The John]

On the Mercury of that HP the idle set screw is on the spark advance lever, not the carburetor control linkage. The manual states that you get in the water with the engine running, F gear, control set to idle, fast idle off, and adjust the screw (timing, white knurled knob ss spring loaded screw) until the tach reads 675 +/- 60 RPM. That speed is designed to get you shifted with the engine still running yet be slow enough to reduce "clunking" and gear wear when shifting.

Thank you, I was just going to reply that I had fixed the issue after getting my manual in late last week.

Thank you everyone for your help and advice.