Engine Power Loss

[Lsnow]

I have a 1985 4.3 OMC I/O. Yesterday, I was on the lake for about 7 hours pulling tubes and skiers without problem until the last run of the day. As we were cruising at about 25 mph, the engine lost power as if I turned it off. I throttled back and the boat started to accelerate again. A few seconds later, it did it again. It happened several times on my way back to the marina so I had to keep adjusting the throttle to keep my momentum. The engine died one time but started right back up. It ran fine all day until that last run. It ran fine at low prm when I returned to the boat ramp and idled just fine as I loaded the boat on the trailer. I had a couple incidents like this the first couple of times on the water this year, but since I drained the gas tank, replaced the fuel filter, and filled the tank with premium gas last month, it ran great the last 2-3 outings.

Also, usually, when I put it in gear and then hit the throttle to take off, like pulling a skier, the motor hesitates for a second then launches and accelerates just fine. Is that because it is carbureted, or is it starving for gas?

Please post your thoughts on how I can fix these issues.

 

[Howard Sterndrive]

Re: Engine Power Loss

sounds like the fuel filter is plugging up, but that was changed - so on to other parts of the fuel system

the anti-siphon valve at the fuel tank would be the first suspect for debris clogging it
you can also check that mud wasps haven't packed your tank vent with mud, but that would not have appeared throughout the day
fuel pump may be on it's way out - look for any gas in the clear/yellowish hose running from the fuel pump to the carb as an indication of a ruptured diaphragm

 

[Lsnow]

Re: Engine Power Loss

I checked the anti-siphon valve, it looks clean. I replaced the fuel filter again and then took the boat out last weekend. It lacked power and the engine was cutting out each time I tried to full throttle, or close to full throttle. It ran great while I was trolling for several hours though. I am wondering if I should replace the fuel pump or clean the carb next, or both. Or, im open to other possible suggestions. There is a rigid aluminum fuel line running from the pump to the carb. I didn't see a clear/yellowish hose. Thanks.

 

[Lsnow]

Re: Engine Power Loss

Today, I removed the carburetor, disassembled it, cleaned it with carb cleaner, put it back together, and reinstalled it on the engine. I also cleaned the air filter. I found the clear/yellowish hose, I followed it to the fuel pump. It did not have gas in it. Before I removed the carburetor, I started the engine. It seamed to hesitate when I throttled it. After I put the clean carb and air filter back on, I startedully the engine again. It seemed to throttle better without any hesitation. Hopefully it runs great when we go skiing in two days.

 

[Cat Dog]

Re: Engine Power Loss

Looking forward to seeing the results as this just happened to me once on my last outing. I am a new owner/operator and have had the boat out less than a dozen times. I have an '88 4.3L. Someone suggested i put an additive called, Seafoam to purge any water that may have gotten into the fuel tank.

 

[Lsnow]

Re: Engine Power Loss

Update: My boat ran great today....for the first two hours. After that, it seemed to run fine while pulling a tube, but then moving from one location to another at wot, the engine started to lose power again. So I thought about removing the air filter to see if that would help. But when I removed the engine cover, I noticed that the trim/tilt motor mounts on the starboard side of the engine had pulled away from the hull and had rotated about 45 degrees. I didn't dare go wot again, so I limped back to the boat ramp, loaded the boat on the trailer and called it a day. Now I have to re-secure the trim/tilt motor mounts then I'm back to the drawing board on the power loss issue.

 

[Lsnow]

Re: Engine Power Loss

Update: I repaired the fiberglass under the trim/tilt motor mounts and re-secured the motor mounts. Test drove the next day, same engine loss power at wot. Then I replaced the fuel pump and tried it again. Boat runs awesome now. 35 miles per hour at 4300 rpm at 7400 feet. Thanks for the suggestions.