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Boat won't run over 38-40 with semi built 351 |
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Seancc1988 
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Joined: August-25-2015 Location: Columbus,ga Status: Offline Points: 10 |
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 Topic: Boat won't run over 38-40 with semi built 351Posted: August-25-2015 at 1:13am |
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Hi everyone! New to the site I own a 86 barefoot nautique with a 454 and a 92 ski centurion true trac open bow. Heard lots about this site and how helpful it is. I wanted a project boat this year because I bought my nautique pretty much done and ready to go. I purchased the ski centurion for 1500 with a locked motor and rebuilt it the trans and painted the boat. The motor is is a 351 .30 over with flat tops and stock rods/crank. Gt40 3 bar heads milled .15, camshaft research camshaft .480 .480 lift, weiland stealth manifold, stock Holley 600 carb, velvet 1:1 trans. With me 175lbs and my fiancé in the boat barely 100lbs it will only run 38-40mph at 4700-4800 rpms. I figured the boat would run as fast or close as my barefoot nautique but boy was I wrong. Any ideas why this boat doesn't run in the 50's? Where they a wet hull boat? The prop is. 12.5x13 3 blade Johnson I wanna try a acme 1459 13x14 prop soon and convert to a secondary metering block for the carb. Shouldn't this boat turn 5200-5400 rpms?
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Jonny Quest
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Joined: August-20-2013 Location: Utah--via Texas Status: Offline Points: 2842 |
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Posted: August-25-2015 at 5:13am |
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First off -- welcome to CCFan. Second off -- we need pictures!
Well, based on what you are describing, somethin' aint right. I'm no expert on the Centurion hull, but if it is anyway similar to a Ski Nautique hull, you should be 48 to 50+ m.p.h. with that motor and the right prop. Based on your description, you should be 300+ horsepower and that should translate into more m.p.h. The RPMs look just a tad low as wide-open-throttle should be 4,800 to 4,900 with a High Output 351W. Some additional info about how the engine is set up would be helpful in the diagnostic process. If you are looking at a carb upgrade, I'd look at the QuickFuel M-650. CARB You won't be disappointed. That M-650 carb is based on the Holley 4150 and has some very nice features. If you want a 600 CFM (based on the Holley 4160) you could look at this OTHER CARB. The right CNC prop will make a noticeable difference. What direction does your prop spin? Clockwise (R/H) or counter-clockwise (L/H) when looking at the prop from the stern of the boat? With your 1:1 tranny that will also indicate engine rotation. I don't think that you want a 13X14 -- waaaay too much prop. JQ |
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Current
2003 Ski Nautique 206 Limited Previous 2001 Ski Nautique Open Bow 1994 Ski Nautique Open Bow Aqua skiing, ergo sum |
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backfoot100
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Joined: January-03-2007 Location: United States Status: Offline Points: 1897 |
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Posted: August-25-2015 at 5:37am |
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Speed is GPS verified? How about the tach RPM? Get a known good shop tach and verify the RPM. What's the duration of the cam? What ignition setup do you have? What's the initial timing set at and what's total advance? Has the engine been properly aligned? We need more information.
That combination should be pulling as hard or harder than your BFN and yes, I would think it should be hitting 50. Don't even think about that 14 pitch Acme. You don't have enough engine for it. You don't have enough engine for a 13x13 Acme. Either a 540 or 541 depending on whether it's RH or LH. Lots here have similar warmed over engine specs with that prop combination. |
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When people run down to the lake to see what's making that noise, you've succeeded.
Eddie |
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backfoot100
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Joined: January-03-2007 Location: United States Status: Offline Points: 1897 |
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Posted: August-25-2015 at 5:41am |
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By the way, welcome and pics would definitely be nice.
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When people run down to the lake to see what's making that noise, you've succeeded.
Eddie |
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TRBenj
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Joined: June-29-2005 Location: NWCT Status: Offline Points: 21109 |
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Posted: August-25-2015 at 8:09am |
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Eddies advice is spot on. Assuming the rebuild wasn't mucked up in some way, it should be in the 300-320hp range. I don't think it will quite hang with the big block (which should be good for 50-51 if it's healthy) but mid-upper 40's with a nice holeshot is probably about right. If your current mph/rpm numbers are at all believable, the current prop should be retired, it's garbage. 541 is the right wheel, the 13x14 acme (1598 or 1458) would be well suited for the bfn- way too much for a 1:1 small block.
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Seancc1988
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Joined: August-25-2015 Location: Columbus,ga Status: Offline Points: 10 |
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Posted: August-25-2015 at 4:31pm |
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Here is my nautique and first boat ever I purchased 2 summers ago for 4500 with 635 hours. First time out with it the coil went out and I thought I had bought a bad boat!
Me getting towed back in first trip out!     Here is my centurion still a work in progress. I have go to get rub rail for it still, add a radio, depth gauge, wakeboard racks and decals. Over the winter id like to change out the prop and carb.   
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Seancc1988
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Joined: August-25-2015 Location: Columbus,ga Status: Offline Points: 10 |
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Posted: August-25-2015 at 4:54pm |
Speed has been verified with my phone gps and my perfect pass system. The ignition setup is a 1 wire hei style that I bought from here http://www.ebay.com/itm/371271627524?ru=http%3A%2F%2Fwww.ebay.com%2Fsch%2Fi.html%3F_from%3DR40%26_sacat%3D0%26_nkw%3D371271627524%26_rdc%3D1 Duration is 216 222 with a 110 lobe separation. I have a new engine harness from skidim and im using all new faria gauges. That's the only way ive verified rpm so far. I have the timing set at 10 degrees when warmed up and idling at 800-1000 on the timing gun. Im not sure what it is when totally advanced. What ball park should it be? I watched a video on how to align the engine and did it myself. I believe it is correct. My prop is a LH prop. Bottom end was built and assembled by a local machine shop. Heads the same and I assembled it all together. The boat seems to plane basically instantly even with 6 people on board there just isn't any top end. |
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TRBenj
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Joined: June-29-2005 Location: NWCT Status: Offline Points: 21109 |
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Posted: August-25-2015 at 5:36pm |
You mean *used to own*, right? 
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Seancc1988
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Joined: August-25-2015 Location: Columbus,ga Status: Offline Points: 10 |
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Posted: August-25-2015 at 6:33pm |
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yep howd you know I sold it? lol he must be on here. Man that boat was more of a headache then it was worth. Trying to save up and sell this centurion next year for a air nautique.
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Hollywood
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Joined: February-04-2004 Location: Twin Lakes, WI Status: Offline Points: 13510 |
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Posted: August-25-2015 at 6:42pm |
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please don't lie to us
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Seancc1988
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Joined: August-25-2015 Location: Columbus,ga Status: Offline Points: 10 |
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Posted: August-25-2015 at 7:22pm |
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I apologize I was mainly just trying let you guys know my back ground and got caught up with typing. I should have specified that I longer had my SN.
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backfoot100
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Joined: January-03-2007 Location: United States Status: Offline Points: 1897 |
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Posted: August-26-2015 at 10:22am |
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800-1000 is way too high of an idle. Should be 600-650 in gear. What carb is on here?
Make sure that carb adjustments are made on the water in gear and warmed up. Secondaries opening at 3800 seems to be too soon. Normally 4K-4200 is when the secondaries will open but if loaded that could make a difference. Fords are more finicky about advance. 10 degree base is good and should be about 30-32 total with it all in by 2800-3K. Others here may confirm that as I'm more of a chevy guy and they like more advance. Dizzy sounds similar to a DUI which several here have installed with very good results but the advance curve is set by the manufacturer so it definitely needs to be verified. Sounds like holeshot and midrange is good. WOT RPM may be a touch low but certainly not horrible by any means. I agree with Tim, that prop is garbage. Sounds like overall timing and performance are good but just missing speed. I would definitely verify the advance curve and total timing and get a 541 prop on there. Tweak the carbs settings a bit and you should be golden. Boat looks cool. |
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When people run down to the lake to see what's making that noise, you've succeeded.
Eddie |
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backfoot100 wrote: