Logo
FULL SITE MENU

1998 2 Stroke 90hp Surging/running rough.

1

109Eastrd

New member
I recently bought a 98 Sylvan Eliminator that had a 98 2 Stroke 90hp Merc. When i first got it I ran the motor on idle with a rich Seafoam and Premium Mixture, until i had almost ran out of fuel (about 1 gallon with a full can of Seafoam). It idled fine at my shop.

I tried to pump out the old fuel from the inboard tank, but there must be a screen that was stopping me from doing that, so i added a can of Seafoam and filled it up with premium from a 1/4 tank.

It ran great, both at idle in the no wake zone, and then full throttle in the open water. I bombed around for about 20 minutes. Slowed down, stopped the engine and had a swim. After that point the engine ran like crap.

Just starting it up again took extremely long, when it finally did start it sat at idle very rough. After a few i pushed the throttle and the motor would surge, up and down, but never quit.

If I shut the motor off, and waited a few, I would get full power at full throttle for about 30 seconds and then (without moving the throttle) it would lose power until it was just idling.

Used my 6hp kicker to make it back, at home checked the compression just to be sure. 120 (or there abouts) on all 3 cylinders.

I plan on changing the fuel filter, adding a water separator. And I was also going to run it on an external tank, to see if that changes things.


Does anyone have any other idea's ? Or has run into something like this?
 
Going to bet your SeaFoam loosened age related contaminants and they have clogged your filter and carb jets.....What you describe is how it works......the Naptha part of it.
 
That's a novel idea. On my Crestliner, the vent is under the black plastic filler cap. Pull the cap, which is vented, and looking down into the hole, I have 2 tubes, one large and one small. If mine were clogged it would be the hole in the fill cap.
 
Change all your fuel lines, I had the same problem, Could hardly blow air threw one of the lines.

I also had added seafoam to mine when the problem started.

Milton
 
Is the oil injection in service ?---Bypassed ?-----Oil output checked ?-----Water pump impeller checked / replaced ?----I would do a compression test to check health of the engine and for future reference.
 
tthomp1334 said:
Change all your fuel lines, I had the same problem, Could hardly blow air threw one of the lines.

I also had added seafoam to mine when the problem started.

Milton
Click to expand...
That was the reason for my question on the filter. I had line problems on my 2002 90 after 10 years, and the filter was full of crud......black specks and tan semi-circular chunks.....carbs had little black specks of fuel line too. Replaced internal and external fuel lines with carb cleaning and new filter.
 
I don’t know about the impeller, raining here today so will let you guys know. Picked up a water separator kit today. My father had the same issue with his, said it was water in the tank. Just curious, would adding an inline fuel filter before the motor be a good idea? The one in the motor was after the fuel pump. Where is the best place to go for old manuals? Thanks for the help so far.
 
Problem with adding things between the pump and the tank is that they can add resistance to the flow of fuel. Resistance not only can limit the amount of fuel, but in hot weather can create a partial vacuum, aka pressure reduction which can allow fuel to boil on hot days and hot operating environments. That process is called "vapor lock"...common in cars back in the days of the Chevy Quadrajet carb. I can speak first hand about that carb and doing what you suggested.....left me stranded on the side of the road, coming back from summer vacation, hot summer afternoon in Texas, station wagon full of kids, boat and all the gear, kids screaming, wife on her last straw......no thank you!
 
So I figured it out. It was an incorrect fuel filter size that caused a burst in the fuel line before the filter, and it was only visible when it was wide open. The Outlet from the Pump and Inlet to the Carb is 3/8 Barb, the fuel filter that was installed was a 1/4 barb. Put in the correct fuel filter size with new fuel line and I had no problems getting it to idle.

It did cost me more, as I installed a Fuel/water seperator anyways. And made sure i had a working external tank with the right hookups.

Thanks for the help
 
Thanks for posting the answer to your problem, some threads read like a novel with the last few pages torn out, you get interested in the story and then never get to read the end. ��
 
Back
Top