Smooth low power 5.0GL Volvo Penta

[Williamboat]

Hello, I have a 2000 Volvo Penta 5.0GL with 2-BBL carb and Prestolite BID ignition system. While out on the water the engine temp was good but was a hot day. When restarting I suddenly had a low power condition where the boat could barely get on plane when previously I was able to get the prop to have cavitation and spike in RPM. I’ve had these smooth low power condition for the past 5 months. I am able to cruise at full throttle indefinitely although used to get to ~5000 RPM now can only get to ~4200. I replaced distributor cap, rotor, ignition coil and spark plug wires. (The spark plugs are fairly new). Timing advances properly in neutral per the manual. I replaced electric fuel pump, used external tank, and replaced power valve, got new fuel bowl and new gasket for metering block. Electric fuel pump is getting proper voltage under load. I pulled each spark plug at idle and each caused change so no misfire at idle. Compression in the cylinders 1,2,7,8 ~180 and 3,4,5,6 ~150. I checked one side for exhaust restriction but was clear. The boat does not have flappers. Both risers are the same temp. The prop is not spinning on the shaft. Every change I have made the boat remains the same. I am wondering if anyone would have any ideas because I am at a loss.

 

[alldodge]

Welcome

able to cruise at full throttle indefinitely although used to get to ~5000 RPM now can only get to ~4200

Do you actually do that?
Your WOT should be around 4800

Compression in the cylinders 1,2,7,8 ~180 and 3,4,5,6 ~150

Don't know how accurate your gauge but that is 30 psi difference on half the cylinders so 18.8% difference. Generally there should be no more than 10% difference. Running at WOT for long periods can distort valves

 

[flashback]

I find it hard to envision an engine at full throttle, not reaching top RPM, but still running smoothly. doesn't make any sense to me

 

[Williamboat]

Y

Welcome

Do you actually do that?
Your WOT should be around 4800


Don't know how accurate your gauge but that is 30 psi difference on half the cylinders so 18.8% difference. Generally there should be no more than 10% difference. Running at WOT for long periods can distort valves

Welcome

Do you actually do that?
Your WOT should be around 4800


Don't know how accurate your gauge but that is 30 psi difference on half the cylinders so 18.8% difference. Generally there should be no more than 10% difference. Running at WOT for long periods can distort valves

I believe it is the type of prop that lets it get up to 5000. So I should adjust the valve train?

 

[alldodge]

I believe it is the type of prop that lets it get up to 5000.

If you get in your car and put it and keep it in first gear the motor will over tach if the computer doesn't stop it.

Putting a lower pitch prop on a motor of your type which does not use a computer to stop the over Rev, get you out of the hole faster but will damage the motor. Which from the sound of it might have happened

 

[Williamboat]

If you get in your car and put it and keep it in first gear the motor will over tach if the computer doesn't stop it.

Putting a lower pitch prop on a motor of your type which does not use a computer to stop the over Rev, get you out of the hole faster but will damage the motor. Which from the sound of it might have happened

Hmm, I’m not sure. Prior to this occurring I was cruising at a moderate speed pulling skiers.

 

[alldodge]

Hmm, I’m not sure. Prior to this occurring I was cruising at a moderate speed pulling skiers.

First I really don't know how the boat is normally driven.

Second if the boat was run at 5K rpm lots of times then this may have caused damage

Third You have more than 10% between lowest to highest in compression test. This means there has been a power reduction

 

[Williamboat]

First I really don't know how the boat is normally driven.

Second if the boat was run at 5K rpm lots of times then this may have caused damage

Third You have more than 10% between lowest to highest in compression test. This means there has been a power reduction

Thank you! I will focus on correcting the compression numbers.