Duo prop propeller choice / RPM issue

[MalibuMike]

I've current got a Parker 2520 boat that has a weight around 6000 pounds. The current prop is a pair of F3's. I cant seem to get the RPM's above 3900 and wonder if I have the right props. The last person to inspect the props noted some corrosion and stated that I could not replace the hubs. Since I may b purchasing new props, wondering which ones to buy and how to figure out if I currently have the right props.

 

[Scott Danforth]

Make sure your motor is up to snuff.

start with a compression test. if youre fuel injected, what is your fuel pressure?

I would expect your boat to have F3's or F4's

 

[MalibuMike]

Make sure your motor is up to snuff.

start with a compression test. if youre fuel injected, what is your fuel pressure?

I would expect your boat to have F3's or F4's

Thank you. Checked pressure and the high and low were in specs. Compression was good in 7 of 8 cylinders but one was about 20 psi below the others. I know the rotor caps are a weak point and replaced one recently but hit max rpm of 3900 with a new one last time I was testing ideas. I need to confirm if the right spark plug was put in. I think I have the vortex version and supposed to use the mr43lts spark plugs. Heard that some shops might just hand out the wrong spark plug if they dont ask which engine you have. Besides new fuel pump, spark plugs, cap and rotor, the only thing I havent changed in the plug wires.

 

[Scott Danforth]

what are the numbers? a new motor is 150 psi, a worn motor is 125 psi, a motor that runs however has no power is 100 psi

which cylinder is low? if you boat in salt water, and the rear most cylinders are low, I would suspect the manifolds may be leaking.

also, how old is the fuel?

 

[BRICH1260]

Sounds like more of a fuel/air or engine electrical problem rather than prop pitch. Concentrate you efforts on the engine before buying new props. Before buying new props, if it comes to that, look on ebay for a good used set. If that solves it, then you can sell the old ones there to offset the cost of the new/used ones.

 

[72fj40]

Confirm the accuracy of the tach. We found the boat tach was off quite a bit at wide open throttle, when compared to the timing light/tach.