Rpm's plummet at 5k on 86' 200 merc

[play2win]

Boat cruises fine under 4500 rpm, at 5k....the engine bogs down to around 2k, and sometimes "kicks in" again before I come off plane. Cannot achieve WOT, thought I was working on only 5 cyl so I checked compression - good, spark all there, replaced in line filter, and water separator. Should I go with plugs now? Thought it was fuel issue, but not quite sure now. Also, took out carbs and cleaned them up last weekend

[johnboy 88 vegas]

Do you have a anti siphon valve on your fuel pickup on the tank? Mine did the same thing cruise fine at 4500 or less but one blast to 6500 and it would die down to 3 grand and run fine until I streched it out again. Put a normal brass nipple on the fuel pickup and problem solved.

[play2win]

What does this anti-siphon valve look like? Its on the gas tank? If it was there all this time, why is that happening now?

[transomstand]

It's a fitting on the fuel tank that the fuel hose attaches to. It has a check ball in it, and fuel flow can pull it closed. Mercury recommends removing it, and install a plain barbed fitting.

This needs to be addressed ASAP, running these engines lean is a sure way to have a meltdown.

[play2win]

Is this it? There is a brass barbed fitting attached to it, and the square looking main part connected to tank with tube (is this the anti-siphon valve)? Is that the part I am replacing? IS there a special type of barbed fittings for gas tank with tube, or do I just unattach tube (I know that wont happen easily) from the existing fitting.

237326

[transomstand]

Looks like you don't have the valve.

[play2win]

Hoping that was it for a nice easy fix........can it be a fuel pump issue??
I dont have a ignition timing light, and if if I did, besides it looking cool, I would have no idea what to do with it..lol

Looks like I may be at the mercy of my marine mechanic, any other ideas??

[transomstand]

Yes, fuel pump is a possibility. Since your there already, yank out that pickup, and see if the screen is plugged. Check the fuel hose for deterioration. The hoses can fall apart inside now because of the alcohol in the fuel.

[play2win]

thanks t-stand, do you mean the screen in fuel pump, ya - i took out diaphragm, cleaned it out, and last week put in new line/primer bc the ethanol ate at it pretty good....did you see the picture I attached of fuel tank valve, its gotta be clicked on (the pic is not showing)

[transomstand]

thanks t-stand, do you mean the screen in fuel pump, ya - i took out diaphragm, cleaned it out, and last week put in new line/primer bc the ethanol ate at it pretty good....did you see the picture I attached of fuel tank valve, its gotta be clicked on (the pic is not showing)

Yep, that's not a valve on that tank, just a plain fitting, so you're ok there. At the end of that plastic tube in the tank, there may be a screen, which should be checked for any obstruction.