Not hitting max WOT RPM

[Frozen]

I can not get my boat to rev higher then 3100RPMs when in gear. In neutral I can hit my WOT RPM of 4200. But in forward I can't. I going about 29mph at full throttle and hit 3100rpm with one other person and myself in the boat. The boat doesn't seem get on plane fast either. Any ideas?

 

[Quint4]

Most of these will apply to your boat:



1. Fuel condition. Type and Octane possibly old fuel
2. Propeller pitch or diameter, damaged blades
3. Restricted fuel pickup tube or anti siphon valve
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
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.

 

[tdschafer]

Wow Quint, That's alot of ideas!! I had the same problem on my 260. It turned out to be the propeller. It was the wrong size and pitch. When I took it to the local propeller shop and told them what boat it was on they told what prop to change to. All was good after that! Todd

 

[springer3]

I have the opposite problem. I have a 3-blade, 19P stainless prop, and the engine will over-speed if I do not throttle back. I am assuming the 4200 WOT limit is for 2-barrel operation, and the 4-barrel needs to close once the boat is at speed. I am making 34 MPH on the GPS when I throttel back to 4200 RPM, so I assume I am making maximum safe power (4.3 liter Alpha I LX).

Missing from the otherwise excellent list is engine compression. It is bad news to find a low cylinder, but it is cheap to check compression, and once you confirm it is OK, any other problem is going to be minor and easy to fix, at least relative to engine overhaul. I have seen many people replace $hundreds in parts before checking compression and learning the real reason for poor running.