Engine RPMs dropping at WOT

[captinmorgan]

I have a 2002 Larson with a 5.0L Volvo and Volvo SX outdrive. When I got the boat it was over propped at 23P so I put a 17P on it. The hole shot is a lot better and I got about 1k more rpm, but now I can not give it full throttle. When I try to give it full throttle it acts like cavitation, but the rpms drop. If it was cavitation the RPMs should shoot up really high. When you give this boat WOT there is a loss in power and then if you pull the throttle back the power will come back. Does anyone know why it might be doing this? Water in the fuel water separator, catalytic converter?

 

[gbeltran]

Re: Engine RPMs dropping at WOT

Did you have the boat out running fine with the 23, switch the prop and have problems, or was it running good with the 23 last year and you swapped props before taking it out this year? A 17 is probably going to be underpropped, that's my opinion. Injected or carbureted? I would say your problem is probably fuel delivery, the filter is easy to change. How long has it been since you've had a tuneup done, fresh plugs, etc?

 

[captinmorgan]

Re: Engine RPMs dropping at WOT

This is the first season that I have had this boat I just bought it. It is a heave boat its a deck boat. When I got it it had a 23p on it and with two people on board it could only do 3k rpm and with a 5 or 6 people (rated for 12) it could not even get on plane, but the engine seemed ok. I talked to others that had a deck boat about this size and they are running right around 18p. We are going to have a lot of people on this boat most of the time so I went one lower with a 17p. I think that before I bought it the owner must have had a prop damaged prop on it and wanted to replace it quick. The reason that I think this is because the 23 looked brand new with not paint missing or anything. I think the owner just slapped one on and it was the wrong pitch. Do you think that the filter could cause this? I know it is an easy and cheap replacement seems worth a try.

 

[gbeltran]

Re: Engine RPMs dropping at WOT

Is it the Gi model engine or the GL engine? There seems to be a number of fuel pump issues with these engines, most likely due to the additional alcohols found in fuels nowadays, stuff ends up clogging the inlet to the low pressure pump leading to failure of that pump and the high pressure one. I'd replace the fuel filter and see what that does. It can be more than that, troubleshooting of the entire fuel system is going to be in order, rather than just replacing pieces. Take a glass jar and empty the contents of the current filter into, you will see if it has water. I'd also think about changing the plugs, especially if you don't have any service records. Sorry to tell you that, but you should be able to spin a 17 well into the 5k range.

 

[captinmorgan]

Re: Engine RPMs dropping at WOT

Thank you for the information. I think thank I am going to change the fuel filter and see if that helps if it doesn't I will have to see if it is the fuel pump. I do not know if it is a Gi or a GL I will look next time I am at the lake.

 

[gbeltran]

Re: Engine RPMs dropping at WOT

Is it injected or carbureted? That's the difference. The injected engines seem to have more fuel pump troubled than the carbureted versions. (different pump assembly).