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Old 07-28-2008, 04:57 PM   #1
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Default Max RPM's and average Speed for a 97 2800 SCR

Hi, I'm fairly new to being a boat owner as well as to this site, although I have posted a few times. My name is Steve and I boat in the New England area (Long Island Sound out of New London, Ct.).

I have a '97 2800 SCR with a single 7.4. The engine max. RPM's are listed as 4,200 - 4,600. I can never seem to get the boat above 4,000 rpm's. At 3,200 RPM's, I'm crusing at an average of 22 kts. The boat comes onto plane a bit slowly, but I suppose 'slowly' is relative. With full fuel, water and 4 adults it is VERY HARD to bring on plane.

I'm trying to get a feel for what should be average for the boat, as opposed for average for 'my' boat. Anyone out there running a similar boat/engine combination? What do you expect to see for average speeds for various RPM's? What is the optimum RPM's for a cruising, and at what speed?

I'm also a bit concerned about the starting sequence. To start, I need to put the throttle into neutral, then give it 3 pumps from 1/4 to full back to 1/4. Then turn and hold the key for about 20 seconds to allow the choke to actuate (listening to that aweful alarm test in the process). Then turn and hold the ignition letting the engine turn over. With the engine turning over, I slowly increase throttle until the engine catches and starts. Most of the time, it won't start until I'm almost WFO. Once it starts, I pull back the throttle back to 1/4 to drop the RPM's and let the engine warm up.
This model 7.4L has a mechanical fuel pump. I've changed the belts and made sure the belt is tight. I don't believe this is a fuel delivery problem.

Is this a typical starting procedure and typical starting behavior?



For all i know the boat is runnign beautifully, I'm just trying to determine a good baseline.

Thanks in advance.
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Old 07-28-2008, 07:31 PM   #2
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welcome to the zoo steve....I own the 2700mpi engine but have had several dealings with carbs....for something like 20 some odd yrs...anyway...what your describing to me is a combination of things...one the choke isn't working properly..and your accelerator pump is either miss-adjusted or the plunger is worn out....so...a good start would be to get the carb rebuilt.....and adjusted properly....secondly....is your boat in the water all the time??...so..the next thing would be to make sure the hull is clean and the props are in good condition...and the proper one for the boat...that boat should have a top speed of about 40 mph...red line on the engine should reach 4600rpm....
with that said.....either your props are wrong ...need a tune up.....timing checked .....and hull clean....
also learn to trim out the drive properly to gain that extra bit of speed......

others will chime in..hope this helps....

SP
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Old 07-29-2008, 01:00 PM   #3
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Thanks for the reply. The boat is in the water all the time. The hull looks good and i try to stay on top of keeping the outdrive and trim tabs clean of growth. I painted the hull this spring and the ablative paint seems to be keeping the hull free of growth as well. I only use the boat on weekends, but it is being used consistantly. Even on plane with a WFO throttle the boat never exceeds 3,900 - 4,000 RPMs. The prop itself is in good condition with no tweaks or dings. It looks like a stock Bravo III prop, and I doubt the previous owner(s) would have changed the prop from stock.

I've taken the cover and spark arrestor of and held the key at aux. and was able to watch the choke close, although it closed slowly, which is why I have been holding the key at aux. for a bit before starting. Even WFO throttle in calm water i can't get the boat above 29Kts at 4,000 RPM's. I've tried in various seas conditions <1ft; 1-2 ft; and on a calm river but there is no difference. I've even run with the tabs up and played with the ourdrive trim. I can see the effects of varying speeds based on how I trim the outdrive, but I'm still trying to get a feel for it.

I'll begin chasing down the accelerator pump, choke and carb, and timing since that would seem to be related to both the starting and running issues.

anyone else out there with a similar boat/motor combo that might be able to share what ther baselines are for their boat?
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Old 07-29-2008, 02:05 PM   #4
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This might be me being stupid but isn't the choke supposed to start closed and then open when it gets +12v on it? ie after it's started and its warming up?
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Old 07-29-2008, 03:06 PM   #5
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gaz..the choke is electrically operated and heated so that it times itself as the engine warms up.....so...he's probably got a tuning problem or some junk on the bottom...this thing is supposed to hit WOT and he's falling short....

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Old 07-29-2008, 06:00 PM   #6
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But shouldn't it be closed when it's cold and open as it warms up. just seems strange how he says he has to wait for the choke to close. or does it work back to front on the bigger engines?
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Old 07-30-2008, 12:42 PM   #7
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You are correct, the choke is closed when it's cold and open when it's warm. When the engine is off, the choke is in the open position. When I turn the key to aux, it slowly closes the choke. I think we're saying the same thing. Then after starting the choke opens back up again as the engine warms up.
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Old 08-05-2008, 11:24 PM   #8
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I just purchased a 2800 scr with the 7.4 mpi last year and although I installed a new engine, I think we can share some info. With 6 adults 60 gal of fuel, 5 coolers in the aft cabin area, we had to move 2 people to the front of the boat and head down wind to get on plane and going into a 10kt wind was useless. We had 2-3 footers at the time. the next day we were on calm waters and the same load, no wind and got on plane much easier. I boat on Lake Michigan at Chicago and am running a 22 pitch bravo 3 drive. What prop are you using? On plane and trimmed out i'm getting 4400-4600 rpm I am not sure what speed i'm running, have to replace the spedo or get gps.
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Old 08-05-2008, 11:56 PM   #9
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sounds like a nice rig.....

SP
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Old 08-06-2008, 02:24 AM   #10
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It came from South Carolina and was in bad shape. but, lots of tlc and a new engine and she is in the water again. One thing I can reccomend when purchasing a boat out of state is go ahead and have the survey but, be sure to fly or drive down to look at the boat before you agree to anything. We were going to walk away from this boat when we went to pick it up, but long story short, we had to take it or fight the dealer in court. It was a matter of having the boat surveyed before we came down and the boat was run during the survey. per their contract we then had to take it, but it was in bad shape and the guy who surveyed it didn't disclose alot of the problems. The exhaust was rusted solid to the heads and the gel was so chalky it looked like white felt with rust stains among other items like canvas etc..
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Old 08-06-2008, 12:09 PM   #11
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The prop is a Bravo IIII, however have no idea what pitch the prop is. IS there an easy way to tell? What is supposed to be stock on that model boat? I definitely can't get the RPM's above 3,900 - 4,000. I've tried playing with outdrive trim and trim tabs with no luck.

I have to replace my exhaust manifolds and risers and the manifolds were rusted on mine as well and needed a lot of 'persuasion' to come off.
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Old 08-06-2008, 03:02 PM   #12
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the markings are on the side of the hub of the props...sounds like you might be over propped but I doubt it...I think between manifold problems and other things...you might need a tune up...that engine should redline between 4400-4800rpm....might need to clean the flame arrestor too...


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Old 08-07-2008, 01:36 PM   #13
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Quote:
What is supposed to be stock on that model boat?
The original prop for the 7.4/B2 was a 17 3/4 X 21.
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Old 08-26-2008, 12:21 PM   #14
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I finally had a chance to check the prop pitch. It's a Bravo III and the props both say 24P on the them. I'm not sure how this would differ from "17 3/4 X 21". I blew out the gunk in the spark arrester. But I still can't get about 4,000 RPM and approx. 29-30MPH.
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Old 08-26-2008, 09:06 PM   #15
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my bravo 3 prop says 20p on it thats a 1999 2800scr i dont think anybody has changed it fron new
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Old 08-27-2008, 05:31 PM   #16
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OK, this saga gets even more odd. I took a look at the parts catalogue:

1996: 2400 SCR; 2700 SCR; 3200 SCR
1997: 2700 SCR; 2800 SCR; 3000 SCR
1998: 2700SCR & 3000 SCR

So according to the Maxum site, they only made a 2800SCR in 1997. This stands to reason, since my boat is a 1997 2800 SCR.

In the parts catalogue they list the following powerplant options:

5.7 LX BII (EK8)
Prop: 18-1/4 X 19 RH PROP

300M C/B2 (7.4L) 2.0:1 (E84)
Prop: 17 3/4 X 21 PROP RH

TWIN 4.3LX GEN+ 1-PC MANIFOLD (EN4)
Prop: 14.5X19 PROP-MERC I/O

280 M EFI/B2 (5.7LX GEN+) 2:1 (ER0)
Prop: 18-1/4 X 19 RH PROP

The parts catalogue doesn't even list the Bravo III option. Obviously the Bravo II props aren't a 24P. So does anyone have any suggestions about how I could confirm the stock OEM prop size and pitch for both Left-hand and right-hand props for the Bravo III? The Maxum site clearly isn't helping me in this instance.

I can't imagine the previous owner when out an spent over a grand to reprop a boat without doing a little research to ensure it's not over propped. There is some old repaired damage on the Starboard strake, so I am beginning to suspect he might have been in a situation where he needed to replace a damaged prop and grabbed any used BIII prop to save some cash.

Any advise or assistance would be gratly appreciated.

Steve
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Old 08-27-2008, 07:09 PM   #17
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my boat neighbor had the 2800 scr and his b3 drive had 24's on the drive..but with that said....he told me he was going for economy...mine is a 20" pitch...my neighbor told me that he had 22's also....which he stated was what came with the boat...


hope this helps

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Old 08-27-2008, 08:47 PM   #18
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my boat is definately a 1999 i think they then renamed it 2900scr in 2000/2001 but it is the same hull my boat originally had a 7.4 fitted the bravo 3 leg is original with 20p props it revs freely up tp 4800 so i think you are oversized at 24p,
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Old 08-27-2008, 09:41 PM   #19
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Quote:
The parts catalogue doesn't even list the Bravo III option.

Your best option is to call U.S. Marine Corp. 360-435-5571. Have your hull I.D. number ready and they will be able to tell you exactly how your boat left the factory. Let us know how they explain the Bravo 3 not being in the parts catalog.
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Old 09-02-2008, 05:13 PM   #20
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I called US Marine, this is what they gave me for stock on a 1997 2800 SCR:

Left Hand: 15 3/4 x 22P
Right Hand: 14 1/2 x 22P

Currently installed on my boat: 14 x 24P

As I understand it, going back to stock props will allow me to reach the 4200 - 4600 RPM range for the 7.4 and will allow me to get on plane much quicker, particularly when loaded with people/gear. It may decrease overall top end speed. He also stated that the current props might be placing a higher load on the engine.
I'm unsure which would be more fuel efficient.


So, with this in mind.............what would you do?
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