Anyone with a healthy mercruiser 3.0 and vacuum readings?

[Mp408]

I have a 2005 Mariah 3.0 SX18 bought it used found out it wont go over 3300 rpms and no power to get on plane.
Prop is Michigan wheel 14x19, 26 mph on phone app.
Read the For adults only been going through it.
Vacuum gauge reads 17"hg at 750 rpm vibrating though.
At 3300 rpm the gauge reads 2" hg also vibrating within 1/2"hg and when you observe down into the carb the fuel is fluttering around below the venturies. ODD
Replaced all fluids and filters and rebuilt carb (ran smoother but not faster)
plugs, wires and cap, adjusted timing, drained fuel tank.

compression cold was 165 on all 4 cylinders within 3 psi
I haven't done a leak down but the intake and exhaust manifold is shared and wondering if the exhaust is bleeding into the intake causing lower numbers and vibration of the needle.

 

[Bondo]

and when you observe down into the carb the fuel is fluttering around below the venturies. ODD

Ayuh,.... Welcome Aboard,.... It obviously has a fuel delivery problem,.....

Ya can't go fast, without fuel to the cylinders,...

 

[Mp408]

It seems odd because I was on plane finally and cruising at 3300 rpm and just enough throttle to not loose speed the vacuum doesn't seem to be high enough to draw fuel into the intake it looked like a piece of glass was were the butterflies would be when closed and fuel was being sprayed up towards it. Seems like back pressure hitting the fuel instead of vacuum pulling it in and disappearing.

 

[Mp408]

May have stumbled upon the problem with the boat not having power to plane and low top speed. When running a prop calculator I put in the variable to see the slippage and realized the apps front screen showed average speed not top speed. My max speed with the 19 pitch prop was 34.2 mph at 3400 rpms and slippage is about 16% if I have a 1.5:1 ratio. The unit is supposed to be 2:1 and that's what it says on it but that's impossible to do with a 2:1 gear. Someone changed the gear ratio causing low power and low rpm top speed!!

 

[Mp408]

Confirmed the lower unit is 1.62:1 based on rolling the motor over. Now need a 15 pitch prop or lower unit with 2:1 ratio.

 

[Scott06]

Should be stamped on left side of drive when viewed from the rear (unless gears were changed). You'd be better off getting the correct ratio drive so you can use a range of props depending on use vs being pigeonholed to a 15" pitch

 

[Mp408]

It is stamped 2.0 the lower unit had been removed judging by the bolts and the speedometer connector isn't a quick connect either. I assumed an impeller change not an entire lower unit.

 

[Bt Doctur]

are you close to central NJ ,exit 9 NJTP exit 127 GSP

 

[Mp408]

Winchester Va

 

[Mp408]

No do you have parts to repair it?