OMC 454 slow and no RPM

[pepin8er]

I have just recently bought a 1993 Chris Craft Concept with a 454 330hp (model 744CPEJUB) OMC king Cobra drive. The motor has recently been rebuilt and bored 0.030". The boat should run 46mph @4700RPM (14 1/2" X 19 pitch) and I can't get it to rev higher than 3800RPM and 35mph with that prop.<br /><br />I have had a mechanic check the carb, gears in the outdrive, compression, changed cap, rotor, plugs and wires. I can install a lower pitch prop and my holeshot is better and RPM higher but my top speed is still only 35mph.<br />While checking the drive, I noticed the boat was in salt water, which the previous owner didn't mention.<br /><br />Other than the lack of RPM, the motor idles great and there is no backfiring . It just doesn't have the power it should. I'm out of ideas and the boating season is coming to an end here in Northern Ontario.<br /><br />Could it be that the wrong cam was installed when the motor was rebuilt?<br /><br />

 

[JB]

Re: OMC 454 slow and no RPM

Hi, Pepin8er.<br /><br />Welcome to iboats. <br /><br />YTou have posted in the Outboard Non-repair forum.<br /><br />I will move this to the I/O Troubles forum.

 

[cc lancer]

Re: OMC 454 slow and no RPM

pepin8er<br />Do you know the speedometer is correct?<br />How much time is on the new engine?<br />Did the mechanic check fuel pressure?<br />Who did the rebuild, are they marine rebuilders?<br />Your engine may be just tight, what temp. are you running?

 

[pepin8er]

Re: OMC 454 slow and no RPM

Hi CC lancer,<br /><br />I used my GPS to get the speed and there is supposed to be 50 hours on the rebuild. <br />The mechanic did not check the fuel pressure but the previous owner had replaced the fuel pump very recently. <br />The rebuild was done by an automotive engine rebuilder. <br />The engine is running at 140 F to 150 F.<br /><br />The guy I bought the engine from has not been forthcoming with information. All he tells me is that the engine was rebuilt and that he doesn't know if the cam was changed. When I bought the boat, the RPM at WOT was 4800RPM according to the tach. Then a mechanich checked the RPM with his tach and found the the boat was only reving at 4000 RPM. Apparently, the previous owner had adjusted the tach to make it look like the motor had the correct RPM's. <br /><br />Thanks

 

[cc lancer]

Re: OMC 454 slow and no RPM

The guy I bought the engine from has not been forthcoming with information.<br /><br />And he didn't replace the fuel pump for lack of something to do, I wonder if this problem existed prior to you buying the boat.<br /><br />Big blocks require a lot of fuel at WOT, this may be the problem, maybe not. You may have to take it to a good Merc. shop and have it checked out.<br />Gook Luck!

 

[pepin8er]

Re: OMC 454 slow and no RPM

What would happen if the previous owner installed a cam for an automotive application rather than marine. The reason I ask is, a mechanic friend said to me that this could be why there is a lack of horsepower. Could this be true?