Sudden power loss on 1988 Merc 90 Hp

[Steve Foss]

So I had the Alumacraft and the tall black Merc out for a workout today. Had last year's gas with Seafoam added last November.

Ran great for awhile. But as I was working up toward peak throttle it suddenly lost power and started missing, and when I maxed out the throttle I could only get about 3/4 the total power I'd been getting, with max RPM of 4400 instead of about 5000.

It idles great and runs smoothly when at highest possible speed, but now it takes several seconds with some stuttering even to build up to the 4400 RPMs I can get out of it. Once there, it runs very smoothly. It's always been fast as lightning out of the hole.

It's a 6-cylinder with two carbs. It has very low hours and has been babied and well serviced its whole life.

Any thoughts?

[Black_Bay]

Would broken reeds cause the problem too?

[marine_man]

I'd definitely try and choke it to see if it picks up... that, or use a rag (hang on to it!) and temporarily restric the air going into each carb and see if it picks up.

marine_man

[Steve Foss]

I'd definitely try and choke it to see if it picks up...

I did, and it didn't.

[broken_line]

be care full about reving it witht the muffs on..if your water pressure isnt high enough you could run the water pump lean, learned that the hard way!

[marine_man]

I know you did this on the hose, but I'd try it on the lake if you can round up some help.

With the added back pressure it's possible a missing cylinder would be easier to hear in the water than on the hose. I'd try pulling spark plug caps off again when the boat's in the water (at idle is fine... sounds like it's missing then too) and see if you can find one or two that aren't contributing.

marine_man