Boat loses power after running WOT for a few hours. Why?

[CaptainMax]

Hello everyone, anyone... Well this is my first post, so here goes:

I feel like I have a fairly unique predicament, my motor is an OMC 5.0L HO in a 1990 Four Winns 200 Horizion. I'm sorry, I dont know the engine year. When I take the boat out in the morning, it runs great! I usually tow a few different people on wakeboards, then get the tube out and tow on the tube for a bit. After a few hours of this, if I head to the beach, or just keep the throttle fully opened, the engine will begin to lose alot of power and it will almost never recover. If I go to neutral, then back to WOT, I remain at around 2000 RPM or maybe a little more. However, SOMETIMES if I SLOWLY ease the throttle up, I can get almost to WOT. I can get the boat back to the marina and then slip the boat. If I go out the next day, the boat runs fine! After a few hours, I get the same problem. What could cause this?

Let me give some background info on the boat and motor:

May 1st, the carb was cleaned out, spark plugs replaced, full inspection and maintenance. Also, my boat does not have a thermostat. The boat never overheats and the gauge reads that it is always cool enough.
Around mid June the boat 1/2 sank (not something I'm proud of) and the entire engine was under water.
After my tragic maritime accident, the oil was changed (once for sure, maybe twice?), boat was of course de-hydrolocked, starter was replaced, batteries replaced, new wire leads to the ignition system, and rebuilt carb.

The fuel pump that I have is not the OEM mechanical pump, I have replaced it with a smaller electrical pump that puts out about 4 psi (I think). When this problem originally began, I thought it was that the fuel pump would "overheat" and conk out, so I replaced it. Of course, after 3 days, the problem started up again.

I went to the list of reasons a boat wont run properly at WOT and a few things were interesting. For instance, having too much oil. When I checked my dip stick, it seemed like there was a BIT too much oil...not much, but more than maybe I should have. How much oil is too much oil? Could it be that as the boat heats up, the oil expands and is blocking the risers?

I guess what makes my situation fairly unique, is that it only happens after the boat has been driven for a while. It isnt as if the boat wont reach WOT from the get-go. Any help is greatly appreciated. If you have further questions from me to help answer my question, you can always email me at EDIT

Again, thank you!

Here is the motor, if this helps:

 

[Bondo]

Re: Boat loses power after running WOT for a few hours. Why?

I feel like I have a fairly unique predicament, my motor is an OMC 5.0L HO in a 1990 Four Winns 200 Horizion. I'm sorry, I dont know the engine year. When I take the boat out in the morning, it runs great! I usually tow a few different people on wakeboards, then get the tube out and tow on the tube for a bit. After a few hours of this, if I head to the beach, or just keep the throttle fully opened, the engine will begin to lose alot of power and it will almost never recover. If I go to neutral, then back to WOT, I remain at around 2000 RPM or maybe a little more. However, SOMETIMES if I SLOWLY ease the throttle up, I can get almost to WOT. I can get the boat back to the marina and then slip the boat. If I go out the next day, the boat runs fine! After a few hours, I get the same problem. What could cause this?

Ayuh,... Welcome Aboard,.... My guess is, there's a fuel restriction, Somewhere....

The 1st place to start is checkin' the contents of the fuel filter for water, 'n crud....

In yer case, the 2nd place I'd look is the tank's Vent line,... look for a restriction in it...

 

[bruceb58]

Re: Boat loses power after running WOT for a few hours. Why?

A quick test to see if it is the vent clogged is to remove your filler cap and run it to see if it does the same thing.

Hopefully, when you rigged up the electric pump, you have it powered through an oil pressure switch so that the pump doesn't run with the key on and the engine not running.

 

[CaptainMax]

Re: Boat loses power after running WOT for a few hours. Why?

Thank you guys for the fast responses!!

As for the fuel restriction: that was my first guess, but I'm not sure where I'd be getting the fuel restriction from. I guess I forgot to mention that I replaced the fuel filter (the big white one) last week. My vent line isnt clogged because when I fuel up at the end of the day I can see AND feel fumes coming from the vent line. The pump is a small electric pump and I'm pretty sure its pumping just as hard at the end of the day as it is at the beginning of the day. I've been told there are a few small filters I should check (ie right before carb bowl, right after fuel tank before fuel supply line), but I just dont see why they would clog up only after the engine has been running for a few hours. The more I think about this problem, the more I think it is either electrical or something is getting too hot and not performing properly.

As for the fuel pump, Bruce, I unfortunately did rig it the "wrong" way. The pump runs if the key is turned and not only based on an oil pressure switch. What are the negative effects of running it this way? Am I over supplying fuel? Could that be my issue? I had a mechanic tell me that rigging it the way I have it is only bad if I were to fall out of the boat and the boat kept running or something. But now I'm wondering if rigging it this way is affecting my performance. And, furthermore, how do I rig it to an oil pressure switch!?

Again, thanks all around!

 

[Howard Sterndrive]

Re: Boat loses power after running WOT for a few hours. Why?

The pump is a small electric pump and I'm pretty sure its pumping just as hard at the end of the day as it is at the beginning of the day.

how are you pretty sure of that? put a gauge on there and verify that assumption.

 

[Scott Danforth]

Re: Boat loses power after running WOT for a few hours. Why?

unfortunately did rig it the "wrong" way. The pump runs if the key is turned and not only based on an oil pressure switch. What are the negative effects of running it this way?

if the motor dies or you leave the key on, the pump keeps pumping. if there is a fuel leak or your float/needle and seat fail, the pump will fill your bilge with fuel. hence the relay pilot off the oil pressure switch.

 

[CaptainMax]

Re: Boat loses power after running WOT for a few hours. Why?

Ok, cool...so now I understand the reasons for doing so, and I will wire it up to a oil pressure switch. I will also put a gauge on the pump so I know what my fuel pressure is. I assume I can just put that in line AFTER the pump anywhere between the pump and carb? Or do I put it right before the carb and after the fuel filter?

But again, I dont think this is solving my problem. The worst part about this, is that it only happens after being out for a few hours, I cant diagnose within the first 20 minutes. That means I have to be out on the lake enjoying a day before I can even start to diagnose lol

I am curious about this excess oil issue. Does anyone have any experience with having too much oil?

Thanks!

ps, Howard Sterndrive, I like that name lol

 

[Howard Sterndrive]

Re: Boat loses power after running WOT for a few hours. Why?

I would follow that steel line back from the carb and look for the first convenient place to tee a gauge in, as close to the carb as possible.
Maybe your electric pump is making too much pressure, pushing past the float and flooding the motor (adding fuel to your oil)

Prolonged running at too high a pressure then causing the overworked pump to overheat.

 

[CaptainMax]

Re: Boat loses power after running WOT for a few hours. Why?

Oh, interesting. Thats a thought. Would a regulator help that? What kind of fuel pressure should I be getting? But if the engine is flooded, it wouldnt still run...or it would? Because the engine never dies...it just loses almost all its power.

 

[Howard Sterndrive]

Re: Boat loses power after running WOT for a few hours. Why?

this is a lot of speculation, but yes. it can run with too rich of a fuel air mixture (flooding). The spark plugs may reveal this if they are black/sooty.

 

[CaptainMax]

Re: Boat loses power after running WOT for a few hours. Why?

Ok, I will look into getting a gauge, a regulator, and checking my plugs.

Also, this is strange, but I think my oil may be a bit too dark? Is that possible? When I checked the oil last week it wasnt milk-shake colored but it wasnt really brown either. It was like almost black. Thoughts? Or nothing to worry about?

 

[HT32BSX115]

Re: Boat loses power after running WOT for a few hours. Why?

if the motor dies or you leave the key on, the pump keeps pumping. if there is a fuel leak or your float/needle and seat fail, the pump will fill your bilge with fuel. hence the relay pilot off the oil pressure switch.

AND the other 800lb gorilla in the room is there'll be a spark that will cause a BIG KABOOM!

You're also operating in a HOT climate (Las Vegas in Summer!)

You could also be getting a vapor lock at some point.

Try running your bilge fan all the time. When you get the problem, open the engine compartment and put your hand on the pump........if it's hot, that may be where your vapor lock is happening. The vapor pressure of most gasolines is around 7-9 lbs. The pump won't prevent it putting out only 4 or 5 psi.

 

[81 Checkmate]

Re: Boat loses power after running WOT for a few hours. Why?

Black oil is dirty oil....... Smell it and see if it smells like gas...... Along with your plugs......

I would look into replacing the fuel pump......thats just an accident waiting to happen....

Just think as your cruising along the motor starts to run like crap and it back fires and motor quits the fuel pump is still pumping raw fuel.

Why not go back to the original mech pump? This may be your problem!

Im just saying!

 

[CaptainMax]

Re: Boat loses power after running WOT for a few hours. Why?

Where could I find the OEM fuel pump?

And can you explain vapor lock?

 

[HT32BSX115]

Re: Boat loses power after running WOT for a few hours. Why?

Where could I find the OEM fuel pump?

And can you explain vapor lock?

http://en.wikipedia.org/wiki/Vapor_lock

http://www.boatfix.com/merc/Bullet/99/99_07.pdf

 

[Howard Sterndrive]

Re: Boat loses power after running WOT for a few hours. Why?

some info about converting a Volvo Penta 5.0 pump
http://forums.iboats.com/showthread.php?t=497453

 

[CaptainMax]

Re: Boat loses power after running WOT for a few hours. Why?

The more I read about vapor lock, the less I think that is my issue. Vapor lock seems to kill the motor and bar it from restarting. In my case, the engine will never fully die, just lose power. Also, I can start and stop my engine as I please. Any other ideas?

 

[Scott Danforth]

Re: Boat loses power after running WOT for a few hours. Why?

vapor lock comes in varying degrees. I have had it fully kill a vehicle, and I have had it deliver just enough fuel to limp along just above idle.

what is the findings on your oil?

 

[john cole]

Re: Boat loses power after running WOT for a few hours. Why?

I would really look at the vapor locking issue. check to see how close your fuel lines are to your exaust system to start, you said that you have installed a different pump in it which means your are not using the steel lines that were in it for the most part i would assume. and like Scott said the vapor lock can come in varing degrees. just curious, do you run your fan while running? that might help take some of the heat away from the engine compartment while your out playing (just a thought). but i would put my money on the vapor lock problem, not really sure about a coil over heating although that could possibly be a issue.

 

[CaptainMax]

Re: Boat loses power after running WOT for a few hours. Why?

Hello Scott boy and John Cole. I live 45 minutes from my lake and so getting out there isnt an everyday thing. I havent been there since I started the post, but probably will go today. If vapor locking is the issue, how do I resolve it? That may be my biggest problem right now. As for my blower fan, I typically run it. I only shut it off if I'm cruising. Low speeds and pre-starts it is always ran. I will definitely check my tubes to see how close they are to the exhaust and try and move them appropriately.

But lets talk for a minute how I can resolve a vapor lock issue. Assuming that is the problem, how can I correct it?

Some more things I've been thinking about: when I do get this issue with the boat, if I put it in neutral and rev the engine, I can get it to rev up very high. Its only when the engine is in drive that I lose this power. Is that important information? Furthermore, when this issue occurs, the engine usually drops its RPM's to a moderately steady rate. It doesnt fluctuate between where it loses the power to. It will always go to the same "power-level". If I'm lucky, I can slooowwllyyy increase RPMs and get more power.

By the way, I'd like to stop for a second and just say thank you to everyone who is trying to help me out. Trust me, everything and anything is all greatly appreciated!