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Merc 357 325 hp ** QUESTION **

2

22partycat

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I purchased from Mercury a 357 325 hp 5.7 engine. It is on a 22 Foot Advantage (Cat) with a Bravo 1. I am running a 22P 4 blade Prop and while testing the WOT I realized that I was not reaching the WOT range of 4400-4800RPM. I am currently running at WOT of 4000, so I am going to get a 3 blade 19P. I experienced something else I was hoping someone could help me with. When at idle speed, and I quickly get on the throttle, it will quickly get to approx. 2500-3000 RPM and no further. I have to back off the throttle, bring down the RPM's and then ease into the throttle to get it up and over 3000 RPM? Could this be a prop issue as well? Thanks.
 
what do you have carb ? Ignition system ?

Here is a great checklist. copied and pasted here.

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
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.
__________________
Don S.
 
Thanks Chief....I definately think it's the prop. I'm gonna go with a 21P 3 blade first and try that. I think a 19P will be to much of a drop.
 
The 4 blade is causing too much cavitation at 3000 RPMs. The 19 pitch X 14.5" - 15" will do what you want. The 21 pitch may make it to 4200-4300 RPMs.
 
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