7.4 454 running sludish at high rpm

Y

ynot

Member
Feb 14, 2010
132
s ca
Boat Info
400 sedan bridge
Engines
454 mer
hello boaters
I have 2 7.4 454 Mercruiser big block
at idle looks and sound good
then when in gear up to 1500 rpm no issues then anything over no power at all
need assistance if anyone experienced same issue
thank you
 
ynot said:
hello boaters
I have 2 7.4 454 Mercruiser big block
at idle looks and sound good
then when in gear up to 1500 rpm no issues then anything over no power at all
need assistance if anyone experienced same issue
thank you
Click to expand...
I had similar problems with my twin 454's. After much screwing around, I installed new plug wires and it made all the difference in the world. I also had new plugs installed, tuned them up and have been enjoying great boating for 3 years.
 
Is this a new problem? Did it begin to happen to both engines at the same time? one or two fuel tanks? If in salt water how long has the boat been sitting in the water and how often is the boat used? Could be the running gear and bottom is badly fowled.
 
both engines, checked fuel looks ok ,and replaced fuel filters .
 
A 400DB is a big heavy boat for gas motors. Describe sluggish. What is your cruise speed @ what RPM.
 
Steve S said:
A 400DB is a big heavy boat for gas motors. Describe sluggish. What is your cruise speed @ what RPM.
Click to expand...
than you Steve
I don't use the boat a lot
I just like to stay at the marina and chill
the fuel is old but looks good after test
on idle both engines sound good even at 2400 rpm no problem
when I take the boat out ,it runs good at around 1200 rpm then when I push on throttles and reach little over 1500 then both engine kind choking with no power what so ever to plain .
few month ago I reached 4500 rpm with good speed
thx again
 
ynot said:
than you Steve
I don't use the boat a lot
I just like to stay at the marina and chill
the fuel is old but looks good after test
on idle both engines sound good even at 2400 rpm no problem
when I take the boat out ,it runs good at around 1200 rpm then when I push on throttles and reach little over 1500 then both engine kind choking with no power what so ever to plain .
few month ago I reached 4500 rpm with good speed
thx again
Click to expand...

I would either haul the boat to be pressure washed or hire a diver for a hull inspection. After that plan on running the boat to get the fuel tank below 1/4 tank and put in a couple of hundred gallons of fresh stabilized fuel.
 
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