Mercruiser 4.3 wont get over 2600 RPM under load

[spocoug]

I recently bought a 1993 23 ft Searay Cruiser with a 4.3L Mercruiser. The engine/boat only has 378 hours on it. When I had it summerized the dealer tuned it up, replaced several out drive seals and the alternator. I took it out on the maiden voyage today and the engine sputtered alot around 1500 RPM and would not get over 2600 RPM underway, even though it ran smooth at that RPM. While in nuetral te RPM's will easily get up to between 5000 and 6000. Granted this isnt a real big engine for this size boat, but it should go faster than approx. 10 mph. I said approximately because the speedometer wasn't working either. This is a beautiful boat in great shape, but I have already spent a bunch of money.

I would appreciate any suggestions of things to check for the slow speed/RPM or speedometer problems.

I searched old posts for the speedometer problem and thanks to a post by BAYLINER185 I have resolved the speedometer problem. The shop had left the small black pressure tube disconnected just above the cavitation plate on the outdrive. I re-connected and blew canned air through the speedo hole, AND IT WORKS! Thanks BAYLINER185

 

[Don S]

Re: Mercruiser 4.3 wont get over 2600 RPM under load

List of possible causes of low WOT (Wide Open Throttle) rpm.

In no particular order

Engine Won't Reach Operating RPM. Check

1. Fuel condition. Type and Octane possibly old fuel
2. Propeller pitch or diameter, damaged blades (if you are missing only 300 or 400 rpm, not 2000 rpm)
3. Restricted fuel pickup tube or anti siphon valve Fuel System Test
4. Crankcase oil volume, high oil level can cause aerated oil and lifter collapse
5. Marine growth on hull and outdrive
6. Wrong gear ratio in outdrive
7. Restricted carburetor air intake (clogged flame arrestor)
8. Restricted exhaust system (broken exhaust shutters/flappers) in engine transom shield or drive
9. Poor cylinder compression Compression Test
10. Carburetor defective, or wrong type.
11. Fuel pump pressure and vacuum
12. Boat overloaded, improperly loaded, or improperly trimmed.
13. Engine Overheating
14. Engine timing and ignition system operation
15. Remote control cables and linkage for proper travel to open throttle plates fully.