1997 Evinrude 90 Slight Hesitation at WOT

I have a 1997 E90ELECM 60deg. It's been running well lately but has always had some slight hesitation when running wide open for a time.

I have done the easy stuff.

First, I replaced the plugs. The wrong type (QL77JC4) were installed. They were replaced by properly-gapped QL78YC.

I thought this fixed it when I tested it last time out. Ran great for about 10-20 minutes, then I putted around and fished for a bit, mostly on the trolling motor, but on the way back it was hesitating again. It's never really bad like I think it's going to stop/stall. I can feel it more than I can hear it or see it on the tach. It's like someone is hitting the brakes briefly and letting them off again.

Today I went through the rest of the easy things.

It's not:
Old/Bad Gas (It's recent no-ethanol 87)
Pickup tube or screen (Removed and re-installed because it's fine)
Anti-siphon valve (there is none - open fitting)
Primer bulb (Replaced even though the one I removed seemed fine)
Fuel filter (Replaced it and o-ring even though the old filter looked fine)

So that says to me I should have good spark and good fuel at the motor.

Before I start throwing things at it like pulling carburetors I thought I'd ask if there were any "it's probably this" opinions. From this point on the service manual gets a lot harder to test/perform (VRO, Carbs, etc).

Thanks.

Motors need a new water pump impeller about every 5 years.----Has that been done ?

racerone said:

Motors need a new water pump impeller about every 5 years.----Has that been done ?

Click to expand...

No, it hasn't. It seems to pee just fine and that's not in the service manual as a possible for "Loss of RPM at WOT."

Keep reading your service manual.-----It will guide you to the issue.

Thanks for the pointer though. The SM does say the water pump should get a rebuild occasionally. I was planning on doing the gearcase oil when it's inside this winter. I'll look at dropping it and doing the pump while I'm there.