Volvo Penta motor won’t go over 3,200 rpm under load

[JordanHorstman]

Hi. I have a Volvo Penta 4.3 GLPWTR 6 Cylinder engine. I am having a problem with the boat not reaching the top RPM. I can only reach about 3200 RPM. It should get about 4200 RPM. I have changed the spark plugs, distributor cap, rotor, and fuel filter. I also did a compression test on the cylinders and that seems fine. I emptied the fuel tank and put in new fuel and that didn’t change anything. I pulled the fuel hose off the fuel pump and that is pumping fuel and the butterflies are opening up on the carburetor and the choke is shutting off after it gets warmed up. What else can I check or do. The engine sounds great and when it’s in the driveway I can get the RPM all the way up but when it’s in the water under load it will not get up to that 4200 RPM. You can call me at 4196150078 if that’s easier. Carburetor model numbers are 3858330. 75006-1. 3088. It’s a Holley carb

 

[JordanHorstman]

I also took my drive off and had the lower unit rebuilt and I put the drive back on the boat myself but I don’t think that would have anything to do with it.

 

[alldodge]

What were the compression numbers?

What pitch prop is on the drive and do you know what the ratio is?

 

[JordanHorstman]

I checked the compressions when the engine was cold and I got 140, 140, 140, 138, 137, 125

i believe it’s a 1.89 ratio. I don’t know the pitch on the prop but I haven’t changed props in 4 years so that shouldn’t be the problem. The exact same parts were bought for the rebuild of the lower unit.

 

[Scott Danforth]

reving in neutral means absolutely nothing. your motor would rev to 5000 RPM in neutral without a load running on your bad cylinder alone with the sparkplugs disconnected on the other 5

your compression is low, you may want to check when warm

you should be able to get to 4600-4800 RPM no problem with a healthy motor and proper props. however your statement of 4200 tied with your low compression numbers point to the motor being tired and over-prop'd

not being able to get over 3200 is the motor starving for fuel. go back to your carb and clean it.

 

[alldodge]

I checked the compressions when the engine was cold and I got 140, 140, 140, 138, 137, 125

i believe it’s a 1.89 ratio. I don’t know the pitch on the prop but I haven’t changed props in 4 years so that shouldn’t be the problem. The exact same parts were bought for the rebuild of the lower unit.

Since you have had the it for 4 years and as Scott said never got to 4800, then your over proped

Your compression numbers are not within 10% of low to the high so the motor has issues. Might have a leaking or blown head gasket.

If a motor is unable to reach max WOT rpm it does hurt the motor over time

 

[JordanHorstman]

Alright thanks guys. I will check what pitch I have on my prop and get a different one. Also will have the carburetor rebuilt.