7.4 only turns 3800 rpms

Larry McDaniel

New Member
Aug 12, 2020
7
Boat Info
2000 SeaRay 240 Sundeck
Engines
Mercruiser 7.4 Bravo 3
I have a 2000 SeaRay Sundeck with a 7.4 Mercruiser Bravo 3 drive. When I first bought the boat it would run 5000 plus rpms. I had to install a new gimbal ring. After that it will not turn more than 3800 rpms. I have replaced plugs, cap and rotor etc. and can not figure out what could be wrong. I did not pull the engine when I replaced the gimbal ring. Any and all help is appreciated.
 
Yes, and using the trailer tilt it will trim to the point of cavitation
 
So probably nothing to do with the ring.. Clean bottom? Checked your fuel pressure at 3800 ? Does it sound smooth thru the rpm range?
 
Fresh bottom paint this spring. As far as I can tell it runs smooth as can be from idle to 3800. I don’t know how to check the fuel pressure.
 
Should be a shrader valve on the fuel rail. Borrow the tool from Autozone. no charge.
 
Thank you very much for that information, I will do that this afternoon.
 
I don't think you should ever have been able to run a 7.4 up to 5,000 rpm. So that shouldn't be your target WOT rpm.
 
Fresh bottom paint this spring. As far as I can tell it runs smooth as can be from idle to 3800. I don’t know how to check the fuel pressure.
Fresh bottom paint in the spring doesn’t mean there can’t be growth on there or something caught around the props. Time for a look-see to rule that out.
 
We have 7.4s on our 2000 340. From spring through fall the hull needs to be cleaned at least quarterly. Clean bottom we reach WOT at the rated 4000 -4400 rpm. Dirty bottom my port side will max around 3800-3900 rpm. The sun on our port side is more intense so the growth is significantly more. At times I feel we could use a cleaning almost monthly.
 
When I first bought this boat it would turn 5000 plus rpms. I don’t know why it won’t now. It’s not a 30 plus foot boat. Every 454 I have ever known has been 5000 rpm capable.
 
When I first bought this boat it would turn 5000 plus rpms. I don’t know why it won’t now. It’s not a 30 plus foot boat. Every 454 I have ever known has been 5000 rpm capable.

If its a 454 Mag that is the upper limit. The regular MPI is as below. Carbs is 4400 I beleive.
upload_2020-8-12_21-24-3.png
 
This is on our valve cover. Do you have anything stamped on yours?

20200124_123300.jpg
 
Finally tested fuel pressure. 42@idle 38@2000 rpms. It’s a MPI and used to turn 5000 rpms, now it won’t.
New plugs, cap and rotor.
 

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