Too much Prop ?

Dieter

Seaman
Joined
Mar 20, 2011
Messages
58
2002 Four Winns 4.3 V6 18 ft horizon. Usually 4 people plus cooler, and 50 lbs of gear. PO had the aluminum prop replaced with an SS one straight from the dealer so i dont think he ever drove it with the factor origional prop, this one is a 14.25 x 21 pitch, dont know the manufacturer. It will turn 3800 WOT, and 32-35 mph max. I think the prop is too much, considering going to a 19. I water ski and pull a tube regularly, I believe this boat has more potential on the max mph. Engine checks out good 145-155 compression on all cylinders, recent carb work, spark plugs etc...Thanks guys
 
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wbc1957

Petty Officer 1st Class
Joined
Apr 26, 2010
Messages
261
Re: Too much Prop ?

What is your gear ratio? 1.84? Horsepower? 185? You aren't giving us enough info. 3800 at WOT tells us there is a problem with either your tach or the engine needs secondary ignition adjustments. Also, do you have trim tabs, or are you fighting to get on plane? I say all of this due to the fact that a 4.3 with good compression should easily gain high 40's in mph with a mid 4500 to 4700 rpm at wot, with a 14 1/4 x 21 prop. You can try a 14 1/2 x 19, being that dropping the pitch will increase your rpm's, but otherwise I suggest you look at the tach and engine adjustments as the problem.
 

Dieter

Seaman
Joined
Mar 20, 2011
Messages
58
Re: Too much Prop ?

190 hp, cant go find the gear ratio, boat is in storage, 1.84 sounds correct. Could the timing being advanced too far cause the low wot? My friend is a mechanic and said he thought the timing was advanced too far this past weekend when we were out on it. thanks again
 

Robbabob

Senior Chief Petty Officer
Joined
Jun 5, 2009
Messages
678
Re: Too much Prop ?

seems the rpm and speed are matching up together, but the rpm should be another 1000 (giving another 10 mph or so). Assume you are trimming out properly. If so, look at timing.
 

Dieter

Seaman
Joined
Mar 20, 2011
Messages
58
Re: Too much Prop ?

Ok thanks for the help. Does anyone know what the stock prop was for this boat ?
 

wbc1957

Petty Officer 1st Class
Joined
Apr 26, 2010
Messages
261
Re: Too much Prop ?

Ok thanks for the help. Does anyone know what the stock prop was for this boat ?

At 190HP you are running the stock prop size and pitch. You can drop to a 19 pitch in a three blade to see some improvement, but you have to watch your rpm's to not "redline" the max WOT limit your specs allow, or roughly 4700 to 4800. I would also suggest you consider a four blade 17 pitch for better hole shots.
 

Dieter

Seaman
Joined
Mar 20, 2011
Messages
58
Re: Too much Prop ?

Ok thanks for the advise I am looking at all my options.
 

craze1cars

Lieutenant Commander
Joined
Dec 26, 2004
Messages
1,822
Re: Too much Prop ?

Link to prop specs for your boat:
http://www.fourwinns.com/past_product/specs

Click 2002, then scroll down to section 08 and download that page. Depending on which 4.3 you have in your boat, it says it was originally spec'd to run either a 21 pitch or even a 23 pitch prop...with top speed in the 50 mph range. So I don't see any reason you should have to pitch down from your 21, UNLESS at some time in the boat's history the outdrive has been changed out to a V8 outdrive with a taller ratio. But with the load you mention in original post you can expect your top speed to drop off a bit from that 50 mph spec, but still it should easily hit 45 mph + with your load...

So several things come to mind as maybes. Maybe...:

-Your prop is not actually a 21 and has been repitched to a larger number.
-Your outdrive has been changed, and it now has a steeper gear ratio than the boat was originally equipped with.
-You have a mechanical/electrical/fuel problem that is limiting your engine's HP output...maybe throttle cable not opening carb fully at WOT, retarded igntion base timing or advance circuit, ignition is missing one cylinder, other?
-You are not trimming the motor out at higher speeds and the bow is plowing.
 

Dieter

Seaman
Joined
Mar 20, 2011
Messages
58
Re: Too much Prop ?

Thanks for all the good advise. I am taking it out this weekend. I will check the timing first but how can I check if it is firing on all cylinders?
 

craze1cars

Lieutenant Commander
Joined
Dec 26, 2004
Messages
1,822
Re: Too much Prop ?

As long as you have a timing light, you can clamp it on each of the 6 wires and pull the trigger just to see if energy is travelling thru them. But that doesn't necessarily identify a bad boot or a bad plug that might be downstream.

So I feel the best way is to just pull them out and look for spark at each individual plug while cranking the engine the old fashioned way.

At the very least pull them all and check color on them to see if one looks noticably different from the others. If all colors are the same and nice and tan, then that means they have all been firing. If one is wetter or different color, that's a cylinder that may not be firing. Also a good opportunity to look at plug color to confirm your carb is delivering proper fuel mixture. Running too rich or too lean can also cause loss of HP.
 
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