this is a question for my father-in-law. hes got a 21 ft. eliminator with a mildly built 454, about 425 HP. it has a berkeley jet 12 jc. at full throttle hes only getting about 3800 - 4100 RPM. is this normal? it seems like he should be getting  more. the guy that built his engine said its probably the jet drive. I know the jets 10 - 15 years old and i dont think its been rebuilt. it does have a diverter on it. so any opinon or advice would be appreciated.

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That being said, is the boat getting full throttle? Is there anything in the pump that would cause it not to spin up? Motor is tuned right? All the plugs in and hooked up?

as far as i know there is nothing in there. the motor was just rebuilt and installed last year so im pretty sure that its in tune

Can you get some info on the build.  What cam, intake, igntion...

Is this something that just started or has it been like this since the rebuild?

What RPM range was he getting before the rebuild?

Wild cam. Without going into whether the valvesprings can keep up with it (Could easily cause that very issue) I'm going after the MSD. Wheres the RPM limiter set at? or modules, I hear those things take those, right?

Ray

Need some important info....


The easiest tool for trying to troubleshoot a low RPM issue is a vacuum gauge, if the vacuum is high (numerically) say 8-10" hg then throttle butterfly issues is where to look. Vacuum secondary?. If the reading is low (numerically again) say 3-5" hg then you have to start looking at less obvious things...I.E. ignition timing, excessive load (cat in pump impeller  ), too much el Bumpo Sticko, weak ignition system (too large of spark plug gap on a high compression deal the spark can get snuffed out at speed) and don't forget the the obvious tach is wrong syndrome...seen it a hundred times...Well a dozen anyways...

Good luck 

GT

Good point GT.

I replaced my tach shortly after I installed an MSD box and my max rpm dropped by about 300rpm    Difference between an old Sun SuperTach and an Autometer.

Sounds like the same differential for an E bay tach versus store bought...

Sorry for the jack...

GT

so is there any way its the jet like the machinist said? is there anything that he should do to a 10 - 15 year old jet? he used to be a mechanic back in the day. if there was an engine problem he probably would have caught it. i will tell him to check all the little stuff and to do a vacuum check on it. thaks for the help!

Normally when a jet pump gets tired, they over rev the engine, they can go the other way, but rare.

GT