how to improve RPM's?

[ratdogs float]

I have a 1989 19 foot Century with a 4.3 merc and an alpha one drive. The tag on the engine states a WOT of 4600 RPM, I am turning only 4000. A salesperson from Cabella's suggested a change of plugs.
Two questions
1. Will that usually help?
2. How difficult are they to change?
I am new to the I/O concept (had an outboard previously) also to help plane out the boat any suggestions on a hydrofoil?

 

[Limited-Time]

Re: how to improve RPM's?

First off when was the last time a full tune-up was done? Second what size and pitch prop are you turning. Third what condition is the boats bottom in?? And last there is a thread here on just your issue. Do a search using Don S as the thread starter.

 

[QC]

Re: how to improve RPM's?

Also, you MUST verify that your tach is right for any of this info to be useful. As LT has alluded to here, if she is running right, the only ways to increase RPM are:

1) Propeller pitch
2) Lose some weight
3) trim properly
4) Repower

Don't even think about a hydrofoil before you get the other stuff right, and then still don't think about it . . . We'll help you find better ways to improve your boat's performance.

Good luck rat boy and welcome aboard!!!

 

[ratdogs float]

Re: how to improve RPM's?

Thanks! the prop is a 14 1/2 with a 17 pitch. Got it NO hydrofoils!

 

[Don S]

Re: how to improve RPM's?

List of possible causes of low WOT.

Engine Won't Reach Operating RPM. Check

• Fuel condition. Type and Octane possibly old fuel
• Propeller pitch or diameter, damaged blades
• Restricted fuel pickup tube or anti siphon valve Fuel System Test
• Crankcase oil volume, high oil level can cause aerated oil and lifter collapse
• Marine growth on hull and outdrive
• Wrong gear ratio in outdrive
• Restricted carburetor air intake (clogged flame arrestor)
• Restricted exhaust system (broken exhaust shutters/flappers) in engine transom shield or drive
• Poor cylinder compression Compression Test
• Carburetor defective, or wrong type.
• Fuel pump pressure and vacuum
• Boat overloaded, improperly loaded, or improperly trimmed.
• Engine Overheating
• Engine timing and ignition system operation
• Remote control cables and linkage for proper travel to open throttle plates fully.

 

[MikDee]

Re: how to improve RPM's?

Thats the link I was looking for to post here, thanks Don