As seen in Speedboat Magazine’s
Nov/Dec 2024 Issue.

Valve Seat Issues

Dear Bob:
I am having issues that keep me out of the driver’s seat of my boat. The engines are 454 cubic inch Mark IV big block Chevrolets. The exhaust is CMI E-tops with the water mixing in the tailpipes just past the transom. The cam is a flat tappet hydraulic with a lift of .540 on the intake, and .565 on the exhaust. Duration is a mild 234 degrees on the intake, and 262 degrees on the exhaust (@ .050 lift). The lobe separation on the cam is 112 degrees. The cylinder heads are GM iron rectangular port (GM049) with larger valves installed. I am using a Holley 800 CFM marine carburetor (list number 9022) with an Air Gap intake manifold. The ignition is MSD Marine with mechanical advance in the distributor set at 34 degrees total advance at 3,000 rpm. The compression ratio is 8.8:1.

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As seen in Speedboat Magazine’s
Sept/Oct 2024 Issue.

FUEL Starvation

Dear Bob:
I have an older Fountain with MerCruiser 502 Magnum engines. Last year, I noticed that it felt like I was down on power and could not achieve full RPM compared to the year before. I think the engines have been getting progressively worse over the years, so I felt that it was just a result of them getting tired.

This year, I took the boat out and the engines seem to be run-ning out of fuel at about 3,000 rpm. They idle OK and I can rev them but when under load, the engines feel like they are running out of fuel.

There is a mechanical fuel pump mounted on the raw water pump. I checked with a local auto parts store and they have a similar pump, but the lever appears to be different. Could this pump be causing the fuel starvation problem?

Randy Sherman
Dallas, TX

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As seen in Speedboat Magazine’s
June 2024 Issue.

502 Mag to 525 EFI

Dear Bob:
I have a 2000 29 Fountain with a Mercuiser 502 Magnum that has been damaged by being frozen. I am getting ready to swap the motor and install a 2004 Mercury Racing 525EFI that I purchased which has been recently rebuilt. What concerns should I have with this motor swap? Is the wiring harness and mounting the same for both motors? Please provide me with any information you think would be helpful. Thanks!

Charles Miller
Sandy, Utah

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