Reduced Revs and Top Speed....

[mrgrumpy]

I would be grateful for any suggestions. I purchased my first boat at the beginning of the year...1999 Searay 260 Sundancer with a 5.0 Mercruiser 220hp.

Becaused of the appauling weather in the UK the boat has only been used 4 times since purchased. Recently I noticed that the battery wasn't holding charge whilst moored and promptly replaced it for a slightly higher spec battery.

Yesterday we took the boat out for the first time in a while and I found that it would not rev passed 4000 rpm, which was only giving a max speed of 25 mph. From my brief experience I believe that the boat used to run at 5000 rpm, giving a top speed of 32+ mph.

Does this sound like some mechanical issue or could it be in someway connected to the changing of the battery? It does seem a little coincidental....

The only other thing I have done is topped up with fuel.

Thanks in advance
Mark

 

[ziggy]

Re: Reduced Revs and Top Speed....

ya need to find out what yer wot spec is. then if it's not reachin wot, here's a pretty darn good list of things to check that dons has provided in the past. thanks dons.....

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 (Full tuneup done recently)
• Remote control cables and linkage for proper travel to open throttle plates fully.

 

[mrgrumpy]

Re: Reduced Revs and Top Speed....

Thanks Ziggy..... I've just realised that i was comparing the performance against the start of the season when the hull was totally clean. People tell me that it not uncommon to see a significant drop in performance, particularly as the boat has been standing in the water for approx 3 months.