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3500-4000 max RPM

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3-legged-dog

Contributing Member
2003 Crownline, 242CR, 350 mag. EFI, Bravo iii. boat is in the water/brackish/Ches. Bay, boat has had little use this year, repairs, timing, weather. last use was 1st week of July after that I had to make repairs. repairs included water pump, alternator, ignition solenoid. After repairs the test drive was good no issues. This Sunday afternoon i run out second time after repairs. Boat starts right up. no wake zone for a 1 mile. Then i hit the throttle full down, moving, moving, tops out at 3500 4000 rpm. i back off, and recheck everything, drive trim, trim tabs. Hit the throttle again. moving, moving, 3500 4000 rpm topping out i keep going and going. finally i get on plane around 4000 rpm and a very long push. i run at 28 mph for a good 10 miles. The boat now top speeds around 28 to 30. but only 4000 rpms. i fish/troll around for about 3 hrs. and same symptoms coming back to dock.

Cant get on plane, rpms max out at 3500-4000. speed on plane 28-30.

i am going to get in the water and check for growth on the underside and drive.

i am going to run the engine in neutral to see if i can get higher rpm under no load.

could the serpentine belt be slipping would that reduce rpms?

boat ran great a month ago after repairs.

what else should i check?

also, i usually keep the boat connected to shore power, main circuit breaker always on charging battiers. This time shore power or boat main breaker is not showing power. everything else working. i will check with marina management. question is asked because could an electrical issue effect the issues i have stated above.

Thanks
 
I see two (2) issues.

1..... something is preventing your engine from reaching WOT RPM.
If nothing has changed re; the engine tune, etc. since last usage, check for possible hull growth.

The boat now top speeds around 28 to 30 but only 4000 rpm.
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2..... for some reason you are wanting to cruise at above 4k rpm!


Cant get on plane, rpm max out at 3500-4000. speed on plane 28-30.
See above.

i am going to get in the water and check for growth on the underside and drive.
Good call!

i am going to run the engine in neutral to see if i can get higher rpm under no load.
Moot point..... you will gain little from doing this!

could the serpentine belt be slipping would that reduce rpm?
If your tachometer is ignition pulse sensing ...... NO!
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i will be checking for hull growth this weekend.

a question, if it is hull growth, which i am hoping for. How would that limit my rpm from the throttle. i would think with throttle full forward i would reach 6000 rpm and the boat would struggle to come on plain.

i dont want to cruise at 6000 rpm, i want to get on plane around 5200 rpm and come off the throttle to 4400 rpm.

how would i do a compression check, special tool,
 
a question, if it is hull growth, which i am hoping for. How would that limit my rpm from the throttle. i would think with throttle full forward i would reach 6000 rpm and the boat would struggle to come on plain.
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Ayuh,.... Because of the added load on the motor, it can't make the horsepower required to turn that many rpms,.....

Most motors are comfortable at a 4800 rpms at Wot,.... 5200 is pushin' the limits of a production built SBC,....
 
....and then put on some good bottom paint. There are good water based ablative paints available these days. Will go directly over any existing ( except teflon containing paints) bottom paint. Just scrape off any loose stuff and do a light sand overall. Follow directions on can to the letter. If you've never bottom painted a boat before, would consider having it done professionally ( not cheap) or have someone who has done this before guide you. Will have to have boat hauled and blocked to do this. Be sure to clean the stern drive and paint it also, EXCEPT sterndrive (and prop) requires an antifouling paint that is COPPER FREE. There are a number of products out there for this as well. Your favorite local marine supply store can help you with choices and tips. NOT the time to buy over the internet.
 
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3-legged-dog said:
i will be checking for hull growth this weekend.
Yes..... again, good call!

a question, if it is hull growth, which i am hoping for. How would that limit my rpm from the throttle.
It would cause a severe drag, which in turn will over-burden your engine as it is currently propped.

i would think with throttle full forward i would reach 6000 rpm and the boat would struggle to come on plain.
You've got the "struggling" part correct........ you just don't have the 6k rpm correct!

i dont want to cruise at 6000 rpm,
I would hope not! That would be a recipe for a shortened engine life.

i want to get on plane around 5200 rpm and come off the throttle to 4400 rpm.
What does your OEM owners manual suggest for a WOT RPM?


how would i do a compression check, special tool,
I would first look at your hull bottom.

If you then decide to check cylinder pressures, there are some "do's" and "don't's" to be aware of.
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