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Hello Everyone,

I am new to the I/O scene and am not too sure if this is right. I just bought a 24' Baja with a 454mag in it and I am only turning 4000rpms. Motor is all stock, no mods. I have had a few people say that it could be my prop, which is a Quicksilver Mirage counter 23P prop. For some reason I don't think it would be my prop causing me to only run @ 4000RPM's WOT. I had a 454 in an older jet that would run @ 5500-6000 rpms all day and that was a stock build motor as well. Any ideas on what it could be? Could it be my prop? I have checked for vacuum leaks and there aren't any. There is a vacuum port coming off of my dizzy that does not have a vacuum line hooked up to it, may that be it? If it is, where would the vacuum line go to? The carb? Any advise on where to start or any ideas would be greatly appreciated!!

Thank you!!!
Bertus​
 

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Hello Everyone,

I am new to the I/O scene and am not too sure if this is right. I just bought a 24' Baja with a 454mag in it and I am only turning 4000rpms. Motor is all stock, no mods. I have had a few people say that it could be my prop, which is a Quicksilver Mirage counter 23P prop. For some reason I don't think it would be my prop causing me to only run @ 4000RPM's WOT. I had a 454 in an older jet that would run @ 5500-6000 rpms all day and that was a stock build motor as well. Any ideas on what it could be? Could it be my prop? I have checked for vacuum leaks and there aren't any. There is a vacuum port coming off of my dizzy that does not have a vacuum line hooked up to it, may that be it? If it is, where would the vacuum line go to? The carb? Any advise on where to start or any ideas would be greatly appreciated!!

Thank you!!!
Bertus​

Bertus,

Please take no offense, but your in a bit over your head...

First...Leave the vacuum port alone. No help to be had there....

Second, your prop may be a little tall, but still think 4000 RPM is short.

Third, verify your tachometer with a known good one..

Fourth, check, or have someone check the ignition timing at over 2500 RPM (this can be done on the flusher) you should be in the mid 30's in degrees before top dead center.

And last of all, fifth, do not ever and I mean ever compare an I/O to a jet again......:|err Completely different animal... :)bit

I will let it slide because you're the new guy....Gotta play nice you know...:)Unsure
 

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Hi Bertus,
I too find your rpm interesting. I have a 454 Bravo, 330 h.p., that is overrevving a 21p stainless prop, I hit 5100 with more on the throttle. I want to try a 23, I believe it should drop my rpm by 400 or so. If you'd like to try a 19 or 21 I have both you can use if you like. They're new aluminum. I'd like to try your 23.
I'm in Long Beach if you want to come down and run in salt water, otherwise I can meet you at Elsinore or something.
 

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And last of all, fifth, do not ever and I mean ever compare an I/O to a jet again......:|err Completely different animal... :)bit

I will let it slide because you're the new guy....Gotta play nice you know...:)Unsure
True, completely different animal. In fact, you SHOULD have your vac advance hooked to timed (throttle) vac port on front of carb. With an outdrive, you WILL have SOME vacuum during cruise - unlike a jet.

Is vacuum advance your problem?? NO. It only comes into play during part-throttle cruise, and disappears at WOT.

ALSO, check your throttle cable. Push the stick all the way forward and make sure you are getting WOT. Naturally, do this with the engine OFF. After the throttle is pushed completely forward, disconnect it at the carb/throttle body and see if you can open the throttle MORE than it already was.
 

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If its a 454mag then it's an mpi. I would check that the butterflies are opening all the way at WOT (engine off please) and also, are you trimming the drive up while at speed?
 

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Are you sure it's a magnum ? My 26' Warlock with a 330hp 454 would only spin 4200 rpm with a 23p quicksilver mirage. 4,000 rpm is too low you may be over proped for your hull even if it is a magnum. If it is a magnum find out what the max rpm is. Maybe other Baja owners on this sight can relay their experiance.
 

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Hello Everyone,
h
I am new to the I/O scene and am not too sure if this is right. I just bought a 24' Baja with a 454mag in it and I am only turning 4000rpms. Motor is all stock, no mods. I have had a few people say that it could be my prop, which is a Quicksilver Mirage counter 23P prop. For some reason I don't think it would be my prop causing me to only run @ 4000RPM's WOT. I had a 454 in an older jet that would run @ 5500-6000 rpms all day and that was a stock build motor as well. Any ideas on what it could be? Could it be my prop? I have checked for vacuum leaks and there aren't any. There is a vacuum port coming off of my dizzy that does not have a vacuum line hooked up to it, may that be it? If it is, where would the vacuum line go to? The carb? Any advise on where to start or any ideas would be greatly appreciated!!

Thank you!!!
Berths​
merc specs 7.4mpi 4200-4600 454 mag mpi 4600-5000 do you have a VST tank on yours my 95 502 did 415hp had one an it gave me hell stalling low rpm vapor locking that was due to bad O rings on the tank also check water temp sensor I could be read low temp could have you in choke mode an be runing rich If you have EFI also your map sensor can be bad causing wot problems it wouldn't hurt to check fuel rail pressure an check each injector make sure all 8 are consitain with spray an an the factory merc MPI don't flow much more after 5200-5500 the cfm drops off I have seen it first hand on the dyno
 

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Discussion Starter #8
Thanks everyone for the input. I am starting to thing that maybe I dont have a 454 Mag, or at least the motor isn't fuel injected, it is carburated, so maybe not an MPI. The cover that goes over the carb says 454 Magnum / Bravo 1. By VST tank, do you mean a fuel tank that is in the belly of the boat? If yes, then yes, that is what I have. Would vapor lock occur if there wasnt a relief vent? My fuel tank has a relief vent that exits right new to the fill hole. @ H2O racer, if you were running a 23P with the same motor/drive set up but in a 26' boat and turning higher RPM's, shouldnt my boat be turning a little bit higher than yours did since its not as long/heavy of a boat? Just thinking out loud here. @ Flat Foot, yes I am setting the trimming up slightly at 4k rpm's and setting the trim tabs as well. I toyed around with them a little to find the boats sweet spot. I will definitely check the throttle cable, I dont know why i didnt think of that :bangmyhead:. @ GT, I always expect a little hazing from someone....lol. I dont take things seriously and you had provided me with a lot of help a long time ago on SCJB when I had my jets.

I am going to check the throttle cable, RPM's at 2500 to see degree off TDC, and verify my Tach's RPM's with another one I have.

Thank you everyone for you feedback!!!!
 

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[QUOTE=bertus951 H2O racer, if you were running a 23P with the same motor/drive set up but in a 26' boat and turning higher RPM's, shouldnt my boat be turning a little bit higher than yours did since its not as long/heavy of a boat? Just thinking out loud here.

A fair comparison would be with a Baja equiped like yours with the same weight load. One would think that your boat would turn higher rpm's than mine but that isn't always the case. I would find a 21p mirage to try. It will bring the r's up.
 

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bertus951 H2O racer said:
no a VST tank is only on the early mid 90s fuel injection motors its a vapor seprating tank it was replaced with the cool fuel system they use now 10X better so if you have a carb then check timing cap rotor an look for corrosion in the distributor make sure the choke is not stuck on fuel filters an be sure your air cleaner is not restricted after all that good stuff an its running good start prolong down an try an see it rpm comes up but I'm afraid that a stock 454 merc carb will only do 4600 max rpm
 

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no a VST tank is only on the early mid 90s fuel injection motors its a vapor seprating tank it was replaced with the cool fuel system they use now 10X better so if you have a carb then check timing cap rotor an look for corrosion in the distributor make sure the choke is not stuck on fuel filters an be sure your air cleaner is not restricted after all that good stuff an its running good start prolong down an try an see it rpm comes up but I'm afraid that a stock 454 merc carb will only do 4600 max rpm
4600 is the recomended max rpm for the carbed 330hp 454. They will spin higher. I've done it but it's not a good idea. Rpm depends on how the boat is proped.
 

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4600 is the recomended max rpm for the carbed 330hp 454. They will spin higher. I've done it but it's not a good idea. Rpm depends on how the boat is proped.
my 06 merc 525 hits the limter at 5400 whipple has a tuned ecm for an it gains 400 or so more but if you want a long life out of your boat don't over rev it your valve springs will start to go first then its all down hill from their
 

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my 06 merc 525 hits the limter at 5400 whipple has a tuned ecm for an it gains 400 or so more but if you want a long life out of your boat don't over rev it your valve springs will start to go first then its all down hill from their
The 454 that I did this in was in a 22ft eliminator not my warlock. I only did it one time to see how fast the boat would go and backed off. I would be more worried about the rods than the valve springs.
 

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@ H2O racer, if you were running a 23P with the same motor/drive set up but in a 26' boat and turning higher RPM's, shouldnt my boat be turning a little bit higher than yours did since its not as long/heavy of a boat? Just thinking out loud here. @ Flat Foot, yes I am setting the trimming up slightly at 4k rpm's and setting the trim tabs as well.

I am going to check the throttle cable, RPM's at 2500 to see degree off TDC, and verify my Tach's RPM's with another one I have.

Thank you everyone for you feedback!!!!
If you are trimming up, then you shouldn't be on the trim tabs at all. You use the trim tabs for dumping the nose down some more, if neutral (zero) trim doesn't give you enough cut for rough water. Tabs cause drag (variable, depending on how much of them you have touching water), and thus - eat power and RPM. If you are trimmed up until you start to lose speed / then back down a bit, you would ONLY use the tabs to settle down some chine walk. You had BETTER NOT be having chine walk at 4000rpm with 330 hp. Mine won't even chine walk up on the steps at 65 trimmed to the hilt!

Leave the tabs alone until you get your top speed worked out.
 

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The 454 that I did this in was in a 22ft eliminator not my warlock. I only did it one time to see how fast the boat would go and backed off. I would be more worried about the rods than the valve springs.
valve train takes more of a beating then the rods when it comes to over reving the valves will stretch an beat up. The seats the springs lose the pressure an lifters fail only time your really going to damage or kick rods is if your throwing boost NOS other bad combos the stock or incorrect rods now long periods of high rpm can be stress full on the bearings an rod bolt/studs main cap mercury is really good at putting good rods in their motors I built a 509 for my 22 Daytona black hawk set up used the 502 415hp efi made 560hp 624ftlb dyno I used maney rods an a bunch of money in valve train an bearings an it have built a lots of hight performance motors an beat the he'll out of them
 

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valve train takes more of a beating then the rods when it comes to over reving the valves will stretch an beat up. The seats the springs lose the pressure an lifters fail only time your really going to damage or kick rods is if your throwing boost NOS other bad combos the stock or incorrect rods now long periods of high rpm can be stress full on the bearings an rod bolt/studs main cap mercury is really good at putting good rods in their motors I built a 509 for my 22 Daytona black hawk set up used the 502 415hp efi made 560hp 624ftlb dyno I used maney rods an a bunch of money in valve train an bearings an it have built a lots of hight performance motors an beat the he'll out of them
Bertus, sorry your thread got jacked. I hope it gets back on track.

Neil450, I didn't ask for an lecture on how to blow a motor. I'm a retired mechanic and may have turned my first wrench before you were born. Your motor build doesn't help Bertus with his dilema. You built your own motor WOW , YAY for you. I'm done with this thread.
 

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Bertus, sorry your thread got jacked. I hope it gets back on track.

Neil450, I didn't ask for an lecture on how to blow a motor. I'm a retired mechanic and may have turned my first wrench before you were born. Your motor build doesn't help Bertus with his dilema. You built your own motor WOW , YAY for you. I'm done with this thread.
you jumped on me on over reving your 454 don't be pissed cause your a old washed up hack job mechanic that works on lawn mowers an the younger guys out build you old timer an I think you know how to blow your own stuff an look back I gave berths the mercury rpm on the 2 different 454/7.4 you old prick
 
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