Too Much Prop Issue?

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Popeye303

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Tested a 2011 Tahoe Q5i with 4.3L mercruiser and 14 x 23” prop. All seemed to be good except WOT resulted in ~3300 RPM & 39 MPH. Two male adults and 1/2 tank of gas with very little gear on board and water & wind were pretty calm. No bogging noted and engine ran fine for the 2+ hours out there (mostly idling and no wake speed).
Could the prop alone be causing this low rpm or is maybe something else also going on (fuel restriction, throttle issue).
Thanks for any thoughts.
 
dingbat

dingbat

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Popeye303 said:
Tested a 2011 Tahoe Q5i with 4.3L mercruiser and 14 x 23” prop. All seemed to be good except WOT resulted in ~3300 RPM & 39 MPH. Two male adults and 1/2 tank of gas with very little gear on board and water & wind were pretty calm. No bogging noted and engine ran fine for the 2+ hours out there (mostly idling and no wake speed).
Could the prop alone be causing this low rpm or is maybe something else also going on (fuel restriction, throttle issue).
Thanks for any thoughts.
Click to expand...
Something really wrong.
You’re pushing 1,200 - 1,400 rpm short of where you need to be. Too much to be a prop

Engine problems, water logged and or operator error
 
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Popeye303

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dingbat said:
Something really wrong.
You’re pushing 1,200 - 1,400 rpm short of where you need to be. Too much to be a prop

Engine problems, water logged and or operator error
Click to expand...
Thanks for the reply.
Long block and exhaust manifolds replaced and carb overhauled in Dec 2022 by a boat shop. Had maybe 20 hours on since then. That’s why I lean toward fuel, throttle, and prop.
What do you mean by water logged?
 
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airshot

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Water logged foam....it can add hundreds of pounds of water soaked up by the flotation foam under the floor. How old is the boat ? Gotta start with basics...compression test on all cylinders.....check engine timming,....is throttle open completely,....good quality spark,...unrestricted fuel flow,...then check the tach to be sure it reads correctly. Gotta have the engine running perfect before changing props. Weigh the boat, if weight is excessive you might have water logged foam. Check stringers and transom for rotted wood in the substructure. If those are wet, then foam will be soaked for sure. Good luck...
 
dingbat

dingbat

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Popeye303 said:
Thanks for the reply.
Long block and exhaust manifolds replaced and carb overhauled in Dec 2022 by a boat shop.
Click to expand...
Why does a motor with probably less than a couple hundred hours of run time need a new long block and manifolds?

Popeye303 said:
That’s why I lean toward fuel, throttle, and prop.
Click to expand...
A prop buys you roughly 150-200 rpm per inch of pitch. At that rate, you need to loose roughly 7” of pitch to recover the rpm. No way…

Motors either run rough or not at all with bad fuel.

The throttle adjustment is a possibly, but then the quality of the boat shop that did the work is suspect.
 
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Popeye303

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Appreciate all the replies. More info:
It’s a 2011, very clean, hull looks to be in good shape. I didn’t notice any leaks in the 3 hours on the water. Very small amount of water in bilge. Got on plane quick and accelerated well.
All fresh water use boat in central Texas. Block cracked in freeze, so long block and exhaust manifolds replaced by marine shop. Carb overhauled at the time. Guy bought new boat and gave this one to son in law/daughter. They used it twice, but have baby and one on the way, so selling it. The past 2.5 years it’s been run in the driveway once every month or two. No maintenance done the past 2.5 years. Kept in covered storage.
Only other thing to note is some rust at the riser/manifold interface. I showed some old timers at West Marine and they didn’t seem too alarmed by it, but I don’t know if that means anything.
Update on prop: confirmed the 14 x 23” is original for this boat. So, not a prop issue.
Seller is going to have it checked out by a boat shop next week.
 
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airshot

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Whether prop was original or not makes no difference. Boats and motors don't just come with a prop. Props are always extra because each boat and motors is different. Once the motor is running at its peak, the prop pitch is adjusted to match the engine rpm.
 
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airshot

Admiral
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Popeye303 said:
Appreciate all the replies. More info:
It’s a 2011, very clean, hull looks to be in good shape. I didn’t notice any leaks in the 3 hours on the water. Very small amount of water in bilge. Got on plane quick and accelerated well.
All fresh water use boat in central Texas. Block cracked in freeze, so long block and exhaust manifolds replaced by marine shop. Carb overhauled at the time. Guy bought new boat and gave this one to son in law/daughter. They used it twice, but have baby and one on the way, so selling it. The past 2.5 years it’s been run in the driveway once every month or two. No maintenance done the past 2.5 years. Kept in covered storage.
Only other thing to note is some rust at the riser/manifold interface. I showed some old timers at West Marine and they didn’t seem too alarmed by it, but I don’t know if that means anything.
Update on prop: confirmed the 14 x 23” is original for this boat. So, not a prop issue.
Seller is going to have it checked out by a boat shop next week.
Click to expand...
If the block has been cracked, it would make maintenance issues come forward....I would definitely want a transom/ stringer check for soft wood.
 
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