350 Chev OMC Loosing power at high RPMs - UPDATE

[HighLineCBR]

I have a 1989 DONZI Ragazza 23. It is my first boat which i have purchased recently. Boat is in good shape and the engine runs well at low RPMs. at high RPMs and cruising speeds boat seems to choke. It looses power and RPMs automatically drop. So far I have replaced spark plugs, ignition wires, ignition cap. At this point Im not sure if this is a problem with the cooling system, or maybe fuel. Boat does not overheat and runs at about 150 degrees. Low RPMs boat runs fine. Chokes at about 3000rpm.

engine does not die, just seems to choke. Once I reduce throttle it runs fine again. Then once back up to high RPMs same thing happens.

What could be the problem?

thanks,

LK

 

[Bondo]

Re: 350 Chev OMC Loosing power at high RPMs

Re: 350 Chev OMC Loosing power at high RPMs

Ayuh,.....

Welcome Aboard,...

It sounds like your Fuel Filters are full of Crap....

Change them,+ Inspect the contents of the take-offs....

 

[HighLineCBR]

Re: 350 Chev OMC Loosing power at high RPMs

Re: 350 Chev OMC Loosing power at high RPMs

i haven't touched the fuel lines yet. I will clean them this week and see if this helps.

Any other thoughts guys?

 

[HighLineCBR]

Re: 350 Chev OMC Loosing power at high RPMs

Re: 350 Chev OMC Loosing power at high RPMs

I also spoke with a few local boat guys about this problem. Some seem to think that this might be a water pump/cooling problem. I was told that there is a safety cut-off switch with cuts off when the engine gets too much or too little water. Is this true? Is there such a safety system on this 1989 5.7 OMC motor?

One mechanic also told me that the risers are not original. Could this be a problem?

 

[a70eliminator]

Re: 350 Chev OMC Loosing power at high RPMs

Re: 350 Chev OMC Loosing power at high RPMs

Quit talking about it and do what Bondo suggested, your going to get all kinds of stupid advise out there. The best info you could possibly get is right here on this forum, these guys know their shTT and will always steer you in the right direction.
I also say the problem is with fuel delivery a very common accurance with i/o's change out your fuel/water seperator filter, it's part of routine maint.

 

[HighLineCBR]

Re: 350 Chev OMC Loosing power at high RPMs

Re: 350 Chev OMC Loosing power at high RPMs

I'll start today. Hopefully get to test it this weekend.

thanks

 

[HighLineCBR]

Re: 350 Chev OMC Loosing power at high RPMs

Re: 350 Chev OMC Loosing power at high RPMs

So i've changed all the fuel lines and filters. I changed the water separator, fuel filter and the carb filter. The carburator filter was very dirty. lots of crap in it. After cleaning everything out I took it to the lake to test.

Unfortunately same problem! At first I thought it would run well and after a while started cutting out again.

After that i took off the Carb and cleaned it out. But this didn't help either.


I talked to s few people and I was told that this might have something to do with me getting fuel on land and not in a marina. They said that the Ethenol content might be doing this. What do you think???

At this point i don't know what could be the problem. Please help!

 

[Bondo]

Re: 350 Chev OMC Loosing power at high RPMs

Re: 350 Chev OMC Loosing power at high RPMs

After that i took off the Carb and cleaned it out.

Ayuh,......

What kinda Carb,..??
How'd you Clean it,..??
Did you install a "Kit",..?? Why Not,..??

So i've changed all the fuel lines and filters. I changed the water separator, fuel filter and the carb filter. The carburator filter was very dirty. lots of crap in it.

How about the Other Filters,... Were they also Full of Crap,..??
New Fuel Lines,..??
Did you Check,+ Clean the Anti-siphon valve at the top of the Tank while you were there,..??

I'm guessing that you Still have Crap in the Fuel System,...... Right from the Tank on maybe....

 

[HighLineCBR]

Re: 350 Chev OMC Loosing power at high RPMs - UPDATE

The carb is a Rochester 4 barrel for a 5.7 GM. I cleaned it with an air pressure hose and carb cleaner. replaces all seals with new ones.

I changed fuel lines and replaced all filters and also added a second bypass filter for extra security. After putting everything back on I ran the boat around the lake (on lod RPMS because it doesnt run on high RPMs). Then i took the carb filter off to check if there may be any junk it it. Filter was clean. the other filters were clean as well.

 

[DukesFin]

Re: 350 Chev OMC Loosing power at high RPMs - UPDATE

I'm guessing one of two things:

Pickup tube is clogged at the tank

or...

Your pump is trying to pump too much gasoline.

I had a similar problem and threw all kind of parts at it, (including a new holley 4bbl carb!), only to find out that the fuel pump was bad (or TOO GOOD), pumping too much fuel.

Put a new fuel pump on and it ran perfectly.

Either way though, sound like the consensus is that you have a fuel delivery/quality problem.

Good luck and keep up with the updates!

 

[chiefalen]

Re: 350 Chev OMC Loosing power at high RPMs - UPDATE

Alright check fuel pump pressure.If your between 4-6 pounds your good.

Try running the boat from a external tank. Fresh fuel.

Still doing it disconnect the esa. Will be harder to shift but let's see if the problem persists. You can disconnect it while your still on the water one plug.

post your results we will go from there

 

[HighLineCBR]

Re: 350 Chev OMC Loosing power at high RPMs - UPDATE

thanks guys. I will try it our this weekend again. Hope all goes well. I'll try the fuel pump.

On this type of engine, is the fuel pump in the tank or on the motor?

thanks

 

[chiefalen]

Re: 350 Chev OMC Loosing power at high RPMs - UPDATE

I thought you changed out the fuel hoses?

You don't know where the fuel pump is? Theres a fuel filter in the pump.

Theres a fuel filter in the fuel pickup. Someone else suggested that.

Tank vent clear?

 

[HighLineCBR]

Re: 350 Chev OMC Loosing power at high RPMs - UPDATE

I did. I changed the lines from the tank to the water separator. Then from that to the mechanical pump then to the carb.

I just wasnt sure if ther is a pump in the tank or not. The tank puckup line i did not change. Which brings up a good point. that might be clogged as well

 

[Boatin Bob]

Re: 350 Chev OMC Loosing power at high RPMs - UPDATE

Bondo also suggested to check the anti-syphon valve which is the fitting at the tank that the pick up line is attached to and also where the line from the tank is attached to, so you've been near it but??? This is a more likely place than the actual fuel line itself.

 

[Cptkid570]

Re: 350 Chev OMC Loosing power at high RPMs - UPDATE

Do what Chiefalen said -- instead of using your boat's fuel tank run a line from your fuel pump (lower starbord side of the motor) to a gas can -- that way you'll know it's good gas and you'll know there is no fuel antisiphon clogs. It could be your fuel pump itself. They can still run the boat, but just not at higher rpms.

You can also install an inline fuel filter that is glass (west marine has them).. with those, you can tell if the carb is getting gas or not.

 

[sarantis]

Re: 350 Chev OMC Loosing power at high RPMs - UPDATE

It's not sure you 'll find anything clogged.I had the same problem and everything looked OK.It took me much study here and out there to find out that at high RPM the stronger sucking of fuel gathers the crap from the tank to the pickup tube's filter(actually it's a grid at the top of the tube) cutting this way the fuel flow.When the strong sucking from the pump stops the crap falls down to the tank again.So first step for me is an external tank or replace your hose from the tank 's outlet to the filter's inlet with a clear flexible hose and put a friend to drive and notice if the fuel flow throught this hose is continuous at high rpm.(But be carefull this flexible clear hose isn't safe so use it only for test.)By the way Haut Medoc had suggested me an external tank but at the same time i had a carb problem that led me to wrong conclusion.

 

[YmeHP]

Re: 350 Chev OMC Loosing power at high RPMs - UPDATE

I have a 1989 DONZI Ragazza 23. It is my first boat which i have purchased recently. Boat is in good shape and the engine runs well at low RPMs. at high RPMs and cruising speeds boat seems to choke. It looses power and RPMs automatically drop. So far I have replaced spark plugs, ignition wires, ignition cap. At this point Im not sure if this is a problem with the cooling system, or maybe fuel. Boat does not overheat and runs at about 150 degrees. Low RPMs boat runs fine. Chokes at about 3000rpm.

engine does not die, just seems to chose. Once I reduce throttle it runs fine again. Then once back up to high RPMs same thing happens.

What could be the problem?

thanks,

LK

Hi, what did you do to solve the problem? I just bought a 89' Donzi Z-22 with the same engine and problem. Thanks

 

[HighLineCBR]

Re: 350 Chev OMC Loosing power at high RPMs - UPDATE

Its been a while since i contributed to this thread, sorry. Heres what i've done so far. Needless to say without positive results.

Replaced fuel pump and got my carb rebuilt. After i got the pump replaced I tested the boat and I thought I got the problem fixed as the boat ran great for about 2 hours while on the lake. Unfortunately after that it started choking again. So i thought OK... it has to be the carb. Well it wasn't.

I did not touch the tank pickup line yet. I will do that this weekend. I will take an external gas can with me and test the boat that way. At this point im really hoping that the pickup line is clogged. Everything else on the engine is practically replaced.

I'll post new results after this coming weekend.

Thanks for the input.

Luke

 

[Cptkid570]

Re: 350 Chev OMC Loosing power at high RPMs - UPDATE

What is the name of it when the gas line is real close to the engine or exhaust and the fuel in the gas line overheats and so the engine doesn't get gas? I know there is a term for that.. I'll probably remember it in the middle of the night when I'm trying to fall back asleep.