Merc 74L Loosing Power

"I have a 1989 SeaRay with a 4

"I have a 1989 SeaRay with a 454. Prior to taking it out this year I started it at home with water running throught the lower unit. It started and seem to run fine. At the lake it started but when leaving the dock when I would accelerate it would bog down and die. I was able to get it re-started but soon it wouldn't even start back up and I ended up pulling it back home. At the time I thought that it might be a fuel problem so I replaced the anti-syphon valve, the water seporator and the fuel filter at the carberator. I also checked to see if there were any in-line filers between the tank and fuel pump and there weren't. At home it started back up and ran so back to the lake I went. It ended up doing the same thing. I took the boat home and checked and found that I had a weak spark. I replaced the coil and plugs. The new coil and plugs made a huge difference as it would always start and seemed to accelerate great. I thought I had fixed everything, so back to the lake I went. For the first ten minutes or so it would run great and accelerate up to speed as it always did in the past. However, after about ten minutes of running it started loosing power on the top end. If I would throttle it back to about half throttle it would again run fine without any noticable problem, no miss or anything. But if I would again accelerate it above half throttle it would start loosing power or bogging down almost like it was not getting enough gas. It sounds strange but at a point right above the point where it would run without power interuption, it seems the engine would surge and then loose power and surge again as the the front of the boat would rise and fall. The rest of the day it ran started consistantly and ran very well as long as we kept it at half throttle or below. At this point I'm not sure what to check. I still think it's a fuel problem, especially because of how it would surge. I've read on this forum that if the fuel tank vent is clogged this can create a simialar problem but I'm not sure where to find it. Could anything else cause this? What about the carborator? Althought I believe it a fuel problem, i'm also going to change the cap, rotor and wires just to make sure the entire electrical system is not contributing to the problem. Any help and/or ideas would be very appreciated. Thanks"

"Check this. Right where the

"Check this. Right where the fuel line comes into your carb there should be a check valve for the fuel bowl (probably has a screw to adjust on the top of the carb right there). It determines how full the fuel bowl is. If this is set too low then your engine will drink all the fuel before it can be replentished in the bowl. Loosen the screw almost all the way out and crank. It will probably dump some fuel into the intake after you shut it off. Tighten the check valve one turn at a time until it doesnt' dump fuel after it is shut off. THis means that your bowl should be full almost all the time. Hopefully this will solve your problem.

Also, I've been go'n through the same thing. Mine ended up be'n a wiring short at the coil. With the engine running, wiggle the wires. Could save you a bunch of time. "

"Other likely areas of concern

"Other likely areas of concern will be ignition coil, fuel pump (check inline pressure) , check filters (one at carb entrance and one at tank probably)."

"Here I go again! Is there a

"Here I go again! Is there a fuel filter BEFORE the fuel pump? If so, that can cuase this problem since, if the filter is dirty, the fuel pump can't suck gas through it without vaporizing the gas--and vaporized gas doesn't pump. Strainer/ water separators (coarse particle removers) can go before a fuel pump, but filters (fine particle removers) should only be located AFTER the fuel pump.


Jeff"

"Thanks Russ and Fastjeff for

"Thanks Russ and Fastjeff for your input. Update. Even though I had changed the fuel filter at the carb a couple of weeks ago, I pulled it out again and found that it was almost completely clogged with some light brown residue. From my expirience, this could account for the problems I was having with the engine bogging at higher rpms and during accelerating. Just to make sure I will be taking out again this weekend to see if the problem disapears. I suspect that it will but being the filter clogged so quickly I must have some junk in my tank and the filter will probably clog up again after a little bit of use. The fuel tank is buried under the floor and requires a lot of work to get out to clean. Is there any other way to deal with getting the gunk out of the tank?"

"I just got a clear inline fue

"I just got a clear inline fuel filter from walmart for about 5 bucks. I installed it inline in a visible place, before the fuel pump. This should help me rule out any of the 'gunk' problems in the future. The only filter I had before the pump was a wire mesh that was jammed up into the fuel pickup hose. Not too effective."