Dirty Hull and WOT

[andrewterri]

Hello everyone, I have a 4.3 MPI ECT in a 196 Monterey. I had a three blade prop which was 14.25x21. the prop was dinged and not really good for what we do, tubing, wakeboarding, ect. I bought a turning prop 14.5x17 4 blade. The RPM is the crazy thing though. Everytime I do a WOT run the RPM is different even with the same people in the boat. 2 trips ago I was at 4800 running about 42mph. Today was 4200 and 35mph. The only difference is the boat stays in the water so the hull is very nasty. I was pulling it every 2 weeks to clean it the best I could until I finally found a dealer in Kansas City who can acid wash the hull the fall. Since I found that dealer I said the heck with it. Could a dirty hull (black and covered in algae) cause this much of a loss? Do I need to go to a 15x15 prop to get my RPM's up because now they are to low? One final question, if you are over propped (to low rpm) and don't run wot is it still hard on the engine?

 

[Scott Danforth]

You have an issue, most likely the fuel system. That is only reason your WOT RPM is all over the place

$5 worth of oxalic acid and a garden sprayer will clean your hull

 

[andrewterri]

something like a fuel pump? How would I start to diagnose an MPI engine. The boat runs great besides that so I don't really know what to start with. I can look and see if these engines have an external fuel filter. If it does I doubt it has ever been changed.

 

[Scott Danforth]

Low WOT stickies have troubleshooting steps

 

[tpenfield]

Were the 2 WOT runs done weeks apart and the hull had grown a beard in between? I’d clean the hull first, and then see if you get more consistent WOT numbers

 

[Bondo]

Everytime I do a WOT run the RPM is different even with the same people in the boat. 2 trips ago I was at 4800 running about 42mph. Today was 4200 and 35mph. The only difference is the boat stays in the water so the hull is very nasty. I was pulling it every 2 weeks to clean it the best I could until I finally found a dealer in Kansas City who can acid wash the hull the fall. Since I found that dealer I said the heck with it. Could a dirty hull (black and covered in algae) cause this much of a loss?

Ayuh,...... No doubt,..... yer throwin' money away runnin' a dirty hull,....

 

[andrewterri]

ya the runs was done just over a week apart. the hull wasn't that bad on the first run because I had washed it a few days before. the second run it was very nasty. I think this is what is killing my rpm and speed along with fuel consumption. do I need to change props to get the rpms up with this dirty hull until I can get it cleaned?