2003 90hp Mercury 4-Stroke Carburated

[OllieC]

Good morning.

I just picked up slightly used 2003 Pontoon with a clean 2003 90hp Mercury 4-Stroke. We had an exceptionally long Winter so it's been laid up in storage since last October.

We just put it in this weekend and it wouldn't hold at idle and would die. I pulled the boat, pulled the plugs, and it looks like a couple plugs in cylinders 3-4 were gummed up. They must have overdone the winterizing spray oil in the cylinders. I removed and replaced all the plugs and it fired up. (we also cleaned the fuel filter and reservoir)

Now it starts, but runs really rough and won't hold idle. Once I warm the engine up, it runs smooth past 2K rpms, but once I get below 1.5K or down to idle, it wants to stall out. It also stalls out when I come off of higher RPMs down to idle - almost immediately. If I gently slow down, it will run rough for a minute and then die.

I've heard that the 4 carbs on this thing can be touchy. I looked at the air box and it was oily and a little dirty. That must have been from some winterizing oil overspray. I did spray some carb cleaner while it was running and it seemed to help a little, but again it still runs rough at idle.

Any ideas? I think it's the carbs. I'm afraid to tear it down because it's my understanding that the 4 carbs need to be re-synced once they're rebuilt. That's beyond my technical abilities.

Anyway, I was just seeing if anyone has had similar issues and if there's a trick to maybe "de-gumming" the carbs (if thats the issue) . IIRC the 75hp of that year is the same motor. I'm at a trade show this week, and will check this thread and try to respond when I can.

S/N 0T786996
2003 90ELPT 4S

Thanks,
Ollie

 

[OllieC]

So in summary….I removed and cleaned the carburetors, changed the fuel filter, drained the gas and put in fresh non-oxy with a concentrate of sea foam. I have a new squeeze bulb and silver hose on order because it’s my understanding the lining deteriorates over time, and I did find black prices in the filter bowl. Runs like a champ……

Glad I could help myself….

 

[ahicks]

I think it's a pretty safe bet the issue is in the carbs. There's a little tiny idle fuel jet that plugs up very easily - the reason you need to ruin fuel conditioner if you aren't using motor daily.

For winterizing, they really need to have the float bowls drained as part of that procedure.

Regarding the need to re-sync after cleaning, that shouldn't be an issue, as long as you don't mess with those sync screws - the ones with the dabs of yellow paint on them. There's no reason in the world to touch those, even when doing a close inspection/cleaning.

 

[OllieC]

I think it's a pretty safe bet the issue is in the carbs. There's a little tiny idle fuel jet that plugs up very easily - the reason you need to ruin fuel conditioner if you aren't using motor daily.

For winterizing, they really need to have the float bowls drained as part of that procedure.

Regarding the need to re-sync after cleaning, that shouldn't be an issue, as long as you don't mess with those sync screws - the ones with the dabs of yellow paint on them. There's no reason in the world to touch those, even when doing a close inspection/cleaning.

Thank you for the pointers. I was planning on draining the bowls. We have long winter layups in the upper Midwest. I didn’t touch the yellow painted screws.