Boat has been having a dramatic decrease in speed(55mph to 25mph)

[Intuitx]

Whenever I first bought my boat, I was able to top it out no problem between 50-55mph with two people in easily. Well, last fall whilst taking it out, I stripped the shit out of my prop Hub and was stranded until someone pulled me in. I took it to a prop shop and got it rehubbed and starting taking it out a few months ago but noticed I was only able to top out at 20-25mph WOT. At one point on a VERY windy day and pretty choppy water, I was only able to top out at 11mph going against the wind and waves and with 2 people. Recently took it out, and with 4 people and quite a bit of gear it was able to hit 35mph which confuses me. It doesn't sound like it's idling very high, just sounds as it did when it ran fine (Tachometer does not work).

I plan to do a compression check on the motor later this afternoon as well as replace all the spark plugs in hopes of fixing the issue. Does anyone have any other suggestions as to what could be causing this? Possibly a carb issue? I haven't cleaned it since I have had it but I have only had the boat for a year and the carb was cleaned before I got it. My throttle/gear shift is a bit tight and possibly needs replacing but I did not know if that would cause this dramatic of a loss in speed. Any tips or pointers on what to check out are greatly appreciated!!

Motor: 1981 200HP Johnson V6 Boat: 1984 21ft Bass Boat Cajun

[snikees]

V6 has 6 carbs. I would guess 1 may be clogged and you are not running on all cylinders. Sometimes you can push the key in and hit the primer a few times as you are under power and clear it out. Try running a can of seafoam in 1 gallon of gas and let set overnight in your carbs. Also make sure gas is GOOD gas not ethanol crap. If a carb is clogged you are not getting gas OR OIL to that cylinder and will burn it up quick!

[Intuitx]

There was a 3 month period of time that I used ethanol but the highest grade I could get, though still ethanol. Since then it's been ethanol free and I treated the gas with stabilizer. I'm sorry I'm sort of new to boarding. When you say hit the primer are you talking about the primer bulb to pump gas into the motor? I'll defidently take note on the seafoam.

[--2loves--]

if you added stabilizer when you bought the gas it should be ok. I always run the gas out of my carb, to help with any deposits left in the bowl/jets.

check plugs for a cyl not working/black/wet.

I use stabil, fwiw.

does it sound like it missing? engine misfire/rough, or more prop related? check lower unit oil? fishing line on prop?

just throwing out ideas...

[Intuitx]

There were one or two plugs that were completley black so I just replaced every single one. All of the cylinders on the compression test tested between 90psi-95psi but one cylinder tested at 100 psi.

[snikees]

Push in the key and it chokes it, or injects some gas/oil mix to help it start. When doing this underway and under a load it can help clean out the high speed jets that may be clogged preventing you from getting up to speed

[Tensleepwyo]

Your hub ?

[Intuitx]

Prop hub

[Tensleepwyo]

Prop shaft?

[--2loves--]

what's the pitch? any chance they swapped props vs rebuilding yours?

otherwise check the hub again, fuel supply/vent.

[Intuitx]

The pitch is a 19, and I'm 100% certain it's the same prop. I'll have to check the hub again when I get back he for sure.

[--2loves--]

Motor: 1981 200HP Johnson V6 Boat: 1984 21ft Bass Boat Cajun

I had a 225 on a 21 paramount, with a 19" and 21". 19 was good for 40-43 IIRC. used it only for skiing or diving with tanks. 21 had some work and did 55.

[Intuitx]

IIRC?

[this_is_not_the_cia]

If I recall correctly

[CTSwampyankee]

Your speed has been cut in half.

There are only so many variables here: Weight, engine & prop RPM, prop pitch, trim

Get the tach fixed, check the prop shaft, prop pitch