1996 Mercruiser 7.4 / 454 300 Slowww

[jake1z]

Bought this boat a couple months ago and pulled it out of the water today to start fixing her up before i winterize it. Boat is a 96 Century Arabian 24 ft. Prop is a 21 pitch 14 3/4. all three corners are slightly bent from hitting something... Tach doesnt work speedo doesnt work. Boat is slow as hell from getting on plane to top speed its just not moving as fast as it should... what things should i check? I plan to get a new prop maybe a 15"x 19 pitch?...plugs, wires, cap, rotor, coil, rebuild carb, rebuild raw water pump, and the gauges.. anything else i should fix and or look at to get its 300 horses working right again?

 

[thumpar]

Re: 1996 Mercruiser 7.4 / 454 300 Slowww

You need to find out your RPM and speed. Fix the tach then GPS the speed. Don't start guessing before you have the data.

 

[HT32BSX115]

Re: 1996 Mercruiser 7.4 / 454 300 Slowww

Tach doesnt work speedo doesnt work. Boat is slow as hell from getting on plane to top speed its just not moving as fast as it should... what things should i check? I plan to get a new prop maybe a 15"x 19 pitch?...plugs, wires, cap, rotor, coil, rebuild carb, rebuild raw water pump, and the gauges.. anything else i should fix and or look at to get its 300 horses working right again?

Howdy,

I would also ensure that the hull is not water logged. If you suspect the engine you might do a compression check just to ensure that you're not dropping a cyl.....

You should also remove the drive to inspect the U-joints, gimbal bearing and check alignment, and drain and refill the drive oil.

I also wouldn't run it until I got a good tach and speedo.


Regards,


Rick

 

[jake1z]

Re: 1996 Mercruiser 7.4 / 454 300 Slowww

how do i check if its water logged some one else suggested that could be a problem.... boat doesnt feel rediculousy heavy, i just towed it with a 5cyl h3 thats not even rated to tow the boat no less the twin axle trailer. it did alright

 

[jake1z]

Re: 1996 Mercruiser 7.4 / 454 300 Slowww

i need to pull the dash apart to check all the gauges... tach should only be one wire to the coil it moves but it will say im idle at 2.5k and pegged at 7k when moving

 

[thumpar]

Re: 1996 Mercruiser 7.4 / 454 300 Slowww

i need to pull the dash apart to check all the gauges... tach should only be one wire to the coil it moves but it will say im idle at 2.5k and pegged at 7k when moving

Check to make sure it is not set on 4 or 6 cylinder. Some have a jumper or switch.

 

[jake1z]

Re: 1996 Mercruiser 7.4 / 454 300 Slowww

didnt see any type of switch on the gauge... cap and rotor both look fairly new should i eplace them any way? wires and coil both look very old and im going to replace both. engine has the thunderbolt ignition. guy who bought my other trailer today owns a marina and said the dmage to my prop would deff cause some reduced top speed.... any idea how the speedo works in these bravo 1's i followed the clear tube all the way to the transom where it exits but i dont see it on the other side. thanks guys

 

[EMC 1810SS]

Re: 1996 Mercruiser 7.4 / 454 300 Slowww

A bent prop will definetly slow things down ALOT depending on how bad........

 

[HT32BSX115]

Re: 1996 Mercruiser 7.4 / 454 300 Slowww

how do i check if its water logged some one else suggested that could be a problem.... boat doesnt feel rediculousy heavy, i just towed it with a 5cyl h3 thats not even rated to tow the boat no less the twin axle trailer. it did alright

It's just one item to rule out. Run it over a truck scale. If it was waterlogged enough to make a difference, it would not be a LOT of water...(I.E. the entire under-deck area saturated.) It only takes 125 gallons of water to equal 1000lbs!

 

[jake1z]

Re: 1996 Mercruiser 7.4 / 454 300 Slowww

ok so im about to order plugs, water pump rebuild, zincs, a new coil, wires, and thermostat kit. should i get anythign else? like i said the cap and rotor looked good. im going to see if i can find a tach some where to see if the wiring is bad or the the tach in the dash. still idles at 2.5k out of the water. also would a 15" x 19 pitch prop be good for this boat... stock is a 14 3/4" x 21.

 

[thumpar]

Re: 1996 Mercruiser 7.4 / 454 300 Slowww

You need to find out what your WOT RPM is currently before you will know what prop works best.

 

[NHGuy]

Re: 1996 Mercruiser 7.4 / 454 300 Slowww

Don't get a 19 pitch til you do the tune up work. What if a 21 is correct? You give up speed. And I'd not do a coil unless yours has a problem. They last a long time.
I just went through a similar problem on my 5.7. Turned out it was ignition wires and wrong timing (not enough advance) causing my weakness. I now have a 19 that's gonna be for watersports and a 23 that's for go fast time. My boat and trailer are smaller than yours but I have been to the scales. I have a galvanized steel single axle trailer. Boat & trailer are 3200 lbs with 25 lbs of fuel. I figure the boat weighs 2500 or 2600. It could not hit 4700 rpms before the wires on a 19pitch. Now I have the 23 coming this week because I can't go wide open on the 19.
Tune that bad boy up and see what you get.
We have some beautiful Coronado's on Winnipesaukee. One guy has a teal on white one that's to die for. I love Century old school boats like Coronados and Resorters.

 

[jake1z]

Re: 1996 Mercruiser 7.4 / 454 300 Slowww

the coil is cheap at only 38 bucks mine looks like its been through hell and back...plus it will confirm that my tach is messed up and that the coil has nothing to do with it. i need a new prop either way b/c mine is bent on all three corners... maybe i can get a way with a cheap alum one for the next season and buy the correct stainless once its back in the water and running right. an alum one should be alright in salt water for a year right?

 

[jake1z]

Re: 1996 Mercruiser 7.4 / 454 300 Slowww

pulled the dash apart there was a switch ont he tach and it was slightly before the 8c mark... i put it so its facing directly on the 8.. nto sure if that was the problem or not... i find out tomorrow when i start the boat up... the fuel gauge that didnt work moves when i attach a wire jumping the sending wire and the ground wire so the gauge should be alright right? same thing with the water temp when i ground the wire out the gauge pins to the right side. how do i go about finding a replacment for ther sender in the tank. thanks for the help so far guys


one more question found the barb on the outdrive for the speedo the tube is not on it but i dont see the tube coming out the trnsom either. is it inside one of the black tubes with the hose clamps around them? sorry for all the questions

 

[dubs283]

Re: 1996 Mercruiser 7.4 / 454 300 Slowww

jumping the posts on the back of the guage tells you the guage is okay but you need to gound the sender wires at the senders - this will tell you if you need to check the wiring

if your engine runs, the coil is fine - if changing the setting dosen't fix the tach, get a new one - or verify rpm with a shop tach on the engine, i use an advance timing light w/rpm setting

fuel sender can be purchased online or at any repair shop, make sure the depth is right for your tank

the speedo tube goes from the yellow barb on the drive through the gimbal housing on the port side, to the port side of the water passage tube - check for broken tube/muskrat damage

 

[26aftcab454]

Re: 1996 Mercruiser 7.4 / 454 300 Slowww

cool boat Jake- I hope you get it sorted out soon.
I have 96 7.4 wBravop3 and it has been a good one.

 

[45Auto]

Re: 1996 Mercruiser 7.4 / 454 300 Slowww

Do a compression test and make sure the engine is good before you waste a lot of money on a trashed engine and parts you didn't need ....

A 14 year old engine could easily be suffereing from rusted out exhausts/risers, rusted cylinders, jammed rings, etc.