Interesting prop situation

[porscheguy]

The boat should perform fine without the fin. The fin is a band aid. You need to find the underlying issue or issues.

 

[Bikestdy]

I have read this thread several times and like has been said things are not adding up right. However I think there is also a confusion in the terms being used. I think while he is saying cavitation, I think what he means is porpoising.

He first said
"The reason i put the fin on there is because without it the boat cavitated so badly it was hardly enjoyable to ride in, I attribute that to hull design I guess. Put the fin on there and its smooth as ever so I wont be removing it."

Then later said
"Without the fin I couldn't come off just about all the way down without it bouncing all over the place."

That doesn't sound like cavitation to me, that sounds like porpoising (though I am no expert).

Second he says
"the 3 blade is a quicksilver 19p that looks like it was damaged before and reshaped"

So we don't know if that prop is even at factory spec or what particular Quicksilver prop it is (could be just a basic SS).
While I am still new, I was told by one brand that prop pitch can vary between brands. That being said, it may need the 21P if I understand what is all being said and he is experiencing.

 

[Bikestdy]

Can you verify that the new turning point prop is stamped as a 19p and that the blade angle is similar to the SS prop you have (pictures might be good too of the props). Just want to be sure it wasn't misboxed/mislabeled and that it's adding to our confusion.

 

[djx02]

Cobalt Owner's Manual (available from Cobalt's web site) shows for a 1989 172/192 with a 4.3 was factory equipped with a 13-3/4" x 21. Aluminum was a Merc Black Max, Stainless was a Mirage.

 

[Slwevo]

Ok let me update on progress as I dont think this is a prop issue at all, after the issues I've been having I decided to go through a few things. I started by putting the old prop back on and quickly realized the problem was worse so I decided to put the 4 blade back on. Now I went into the fuel system and found the carb filter was full of sand and took the top off th carb and saw the bottom had sand in it. Took carb off and the power valve had sand stuck in the holes. Rebuild carb and tested on water. Boat ran awesome in every way with much more power and the 4 blade was cruising at 30mph and 3500 rpm. Another issue now is when I punch it, rpms jump up to about 4200 and then it starts surging from 4200 down to about 3800 and back up again. If I pull back throttle to about 3/4 it settles at about 3700 rpm and runs just fine but ask it for a little more and it surges. Though I might still have fuel issues and rechecked filter on carb and was clean. Went ahead and installed a water separator and lake tested and same issue. Now I replaced all fuel lines and the anti syphon valve and waiting for good weather to test. So as of right now boat runs great but asking for wot and it surges slightly. So awaiting lake test to see if valve fixes it.

but yes I did mean pourposing earlier not cavitation. Sorry got caught up in the lingo.

also am going to ditch the fin for smart tabs when I get engine running correctly. Which I'm hoping it is now just haven't tested. I will post back with resolution as I get angry when I see similar issues as no update to progress.

again thank you to those who contributed time to my situation.

 

[89retta]

Good to hear that you solved some of the problem . And that you have a game plan. Have you checked your distributor ?

 

[QBhoy]

Getting somewhere now. Makes more sense for the engine to be the issue. Hopefully you get it sorted. Start with the basics and plenty of folk able to advise on here. Good luck.

 

[porscheguy]

It sounds like you’re still having fuel delivery issues.

 

[Slwevo]

Ok was able to take it out to the lake yesterday and it ran perfect, but now I'm convinced my tach is on it's way out.. at full throttle it's only reading about 4200 rpms still and motor sounds and runs good as ever. I tried turning the dial on the back and cleaning all connections to it. It doesn't jump around or anything but I feel like its revving higher then it shows. I dont have the proper tools to bench test it so I'll save for new gauges and just keep cruising at about 28mph as its feels good there about 3/4 throttle maybe a little less. In the meantime I'm going to start another post in another section to see if I can get help on what size push button breakers this thing has, they are so old there is no stickers or any indication on them what size they are. Replacing cause they broke off where they mount from dry rotting and hanging there.

again thanks to everyone who has helped