Won't Reach WOT! Please Help!

[1000dollabill]

Re: Won't Reach WOT! Please Help!

Yes, the boat has two speedos, and speed was verified by gps as well as paced by another boat. The tach reads normal without load, how could it be off with load? There's no way it free revs to 6,000+ rpms. the block numbers (not intake) correspond with a 351w. Tried the 302 firing order just for shi+s and giggles, wouldn't run. The block, heads, valve covers, intake are all sporting the factory Indmar stamps and silver paint. The carb has been gone through a dozen times, as well as the ignition system. The trans has an ID plate "borg warner 1:1." The prop is stamped 13X12LH. Not sure what the boat weighs, but there is little to no foam in it. The trailer is squatting a little bit, probably because it is an older single axle designed for a shorter, smaller boat. Previous owner said it ran 50+mph.

If it had a vacuum leak it wouldn't idle as well as it does. Checked vacuum last season off the intake. Also did an old school propane test to check for leaks.

It's backfiring out the exhaust because it doesn't actually run at WOT, merely 3/4. If I push it to WOT it howls and will eventually ignite the unused fuel in the exhaust.

Every boat I've owned has been gear limited, could be run at WOT all day if you were the gambling type.

I'm fairly convinced it's the prop causing the howling. From what I've read cavitation produces a vibration and sound. The prop has pitting, edges are rough, and the blades surfaces look like some took a torch to the center of each blade.

I'm just west of Atlanta. Any local gurus want to take a spin?

Just a note I've rebuilt my own motors and transmissions for about 10 years now. Cars, trucks, atv's, and a couple lawn mowers. My pops has been an auto mechanic for 30 years and he's stumped.

The guys at SKIDIM (Discount Inboard Marine) worked with me quite a bit last season, said the only thing left is the prop.

I'm buying a prop tomorrow, worst case it's always a good idea to have a spare.

The motor runs perfect, so I'm looking farther down the drive line.

Not dismissing suggestions, but some contradict my tests last season.

 

[Maclin]

Re: Won't Reach WOT! Please Help!

I misunderstood something from your first post that made me think you said you knew your drive ratio was not correct, sorry. But the tach reading cannot be correct in my opinion. The tach could be having an internal problem and could affect ignition also as it is more than likely hooked to the negative coil terminal.

If my engine was putting enough raw fuel in the exhaust to eventually ignite I would not describe it as running perfect. There is still something not right in the ignition or fuel delivery/metering systems I would think. What do your spark plugs look like?

 

[QC]

Re: Won't Reach WOT! Please Help!

DUDE!!!! YOUR TACH IS WRONG!!!!! Tournament boats do NOT go 50, even with Big Block MPIs!!!! YOU CAN NOT GO FASTER THAN THE SHAFT RPM X PITCH. IMPOSSIBLE!!!!! Something isn't right, either the RPM or the gear ratio (it's right) or the speed (I trust that) or the pitch, but for this to be right it would have to be close to a 17 inch pitch . . . How's your power out of the hole?

This is absolutely the most caps I have EVER used in a thread. I am not angry, but you NEED to listen . . .

They are not "gear limited", they are power limited by pitch AND gear ratio. ALL OF THEM if they are propped right. We promise we know of what we speak. Go here and read this prop test info. Prop Test Yes, it's a Mastercraft, but heck maybe, just maybe it's a LOT like your boat. Love you man, but again, we are trying to help. If nothing is wrong, then why not just run it . . . Personally I think it's close to right, maybe slightly down on power or the prop is a POS. If you buy a prop don't go below 12" or you will be sorry . . . Oh, oh, the needle of your tach may swing way up with a blip. So what? Tachs are off by a percentage. Very hard to tell at idle unless you can "hear" 50 RPM . . . But without a good tach reading we are spinning our propellers (wheels). You find a Small block Tournament boat (not a barefoot boat) that runs 50 and I'll eat my hat. BTW, it's a really cool iboats hat that I really like, so I am super confident I am not saying your prop is good. Sounds like a POS, but you have to have the tach checked. Use your Pops shop tach. I agree you need a spare. Get a 12" one!!!!

Oh, oh and get the wake plate UP for testing . . .

 

[whywhyzed]

Re: Won't Reach WOT! Please Help!

......

 

[1000dollabill]

Re: Won't Reach WOT! Please Help!

I am indeed listening and I will check the tach first chance I get, however I'm out of town most weeks. The reason I say the tach cannot be that far off is because I know what a small block V8 sounds like at different rpms. Maybe not to a T, but there is a significant difference between 3000 and 4000 rpms. Never used the tach in any of my cars, quads, or bikes. Also, my secondaries should be opening a noticeable amount around 3400-3600 rpms under load, and they're not. Vacuum is good, and the diaphram is still intact (brand new with a check ball).

Further, I'm not trying to make a race boat out of a ski boat. The goal is 44mph at 4400rpm's. I realize I wont get there until the boat is thoroughly waxed etc. The problem is that I can't get to WOT. Something is loading up the drivetrain and holding it back. I need to weigh the boat still. Hull is clean with a few nicks, and could use some wax. Could be over propped (see pics below forget the stamp.) Boat runs great like I said. Idles at 700 like a champ, revs up clean without breaking up. I justify the backfiring out the exhaust because I know marine carbs are tuned to run rich. Put that on top of the idea that the secondaries are nearly ready to kick in (add that extra air and a marginally greater amount of fuel), and yes, at ~3200 rpms I'm running fat. It takes a good 5 minutes of resonance before I get a barely noticeable pop in the exhaust. I've pulled the wires of the coil one at a time to make sure it caused a miss, as well as put a timing light to each wire to make sure all are kicking. Checked my timing, advance, and changed plugs god knows how many times.

I am certain that my fuel and ignition systems are 100%. Compression is good. Thus leaving me to believe it's somewhere in the driveline (or possibly weight related.)

I spoke with a marine mechanic (friend of a coworker,) and he said he'd be more than happy to take a spin and look at it (free of charge.) However he's two hours away. When we spoke he said it sounds like the engine is in order. He suggested that the resonance (howling) could be the prop, bent prop shaft, or even a tweaked skeg disturbing flow to the prop. Between the prop's condition, a tweaked skeg or shaft, any of these could cause a vibration and cavitation. I don't know if this boat has ever run aground, but I know the punk beached it a lot. I think I'd be best to meet him with a prop in hand, but he's trying to find one from one of his "Old School Inboard Guys."

I know the engine's not winding out, and she's definitely got more left in her. But, I will certify that the tach is correct (at least close,) ASAP. As far as the hole shot it keeps up with a 18.5' runabout with a 4.3L, seeing as this is my first tournament boat, I would think it would dust the play boat. Takes an hour to get to the lake so I try to be prepared to rule out as many possibilities as I can in one outing. I also only have a one day weekend, at least recently.

Thought since I just got home I would post some pics. First is the boat underway ~30MPH, rest are of my prop. I'm pretty sure this prop needs replacement, it's definitely seen better days. I'm stubborn, I know, but I sincerely appreciate ya'lls input. It's tough to fix a boat over the internet, and even tougher when you're three states away from the boat.

 

[QC]

Re: Won't Reach WOT! Please Help!

^^^ Pah, duh, duh, chish ^^^

Edit: That was for whywhyzed

 

[QC]

Re: Won't Reach WOT! Please Help!

I happened to be on when you were posting . . . I was thinking drive-line stuff too. But all I have been trying to say that it is not Possible, make that, Physically Impossible for a 12" pitch prop to go 40 MPH at 3200 RPM shaft speed . . . even if there was no boat attached to it . . . 40 MPH is faster than 12" rotating at 3200 can propel itself. This is a mathematical equation. If this was a hydroplane that weighed 200 lbs it couldn't do it. There is absolutely no other point to my posts. Good luck. Someone did mention that an ignition issue could also show up in the tach as they are coil driven . . .

That prop is looking pretty skanky . . . I guess the other thing is that talking performance and propellers without a good RPM number is useless, so if we know one of these numbers is wrong . . . well I'm just trying to get you to backup before you make yourself crazy and blow some $

 

[1000dollabill]

Re: Won't Reach WOT! Please Help!

yup, I used the calculators online when I was looking at props. I know the math doesn't add up but if you look closely at the outer edges you can see they are noticeably rolled toward the rear of the boat, about an eighth of an inch. Wondering if this is normal? Could it effect the pitch so drastically? I know it has to be out of balance. Hard to check the tach without being in the water. The old garden hose can't even attempt to keep up with anything but idle. Just refinished all my teak last weekend, so I still need to toss it back together.

Thanks.

 

[45Auto]

Re: Won't Reach WOT! Please Help!

The reason I say the tach cannot be that far off is because I know what a small block V8 sounds like at different rpms.

Either your ears/tach is wrong (RPM), the speedos/GPS/chase boat is wrong (MPH), or your prop pitch number is wrong. You'll never get to your goal unless you know where you're starting from!

Lots of props around here that look worse than yours and have very little effect on the boat. I'll be surprised if a prop change fixes it, but it never hurts to have a spare. My experience with cavitation and ventilation is that it UNLOADS the engine, allowing it to over-rev.

Also, my secondaries should be opening a noticeable amount around 3400-3600 rpms under load, and they're not. Vacuum is good, and the diaphram is still intact (brand new with a check ball).

If your set up was right and your engine was truly under a load serious enough to bog it down to 3200 RPM, those secondaries would be open. Sounds like something isn't set up right on the carb.

 

[SimpleM]

Re: Won't Reach WOT! Please Help!

I know I'm a newbie and an I/O guy, but the prop "looks" to me like it's on backwards. I thought leading edge had more length than trailing. Maybe just an optical illusion.

 

[QC]

Re: Won't Reach WOT! Please Help!

Inboard Ski props are weird. Look at the Prop test link I posted above ^^^^^

 

[Maclin]

Re: Won't Reach WOT! Please Help!

At this point I would try a lighter spring in the vacuum secondary housing, also make sure all of the passages are open into the housing and all is installed correctly. At first from your descriptions I thought the secondaries were opening too much too soon. But after a few more details I am with 45auto, they should be opening by then. The 2bbl portion will lean out as it is outpaced, not fatten up, this could explain the pop out the exhaust, lean mixes will not ignite well at rpm.

 

[QC]

Re: Won't Reach WOT! Please Help!

Whew! Almost had to eat my hat . . . BTW, 20% slip @ WOT, 10% at most efficient cruise. Good data

 

[45Auto]

Re: Won't Reach WOT! Please Help!

Excellent data QC! I was looking for something similar but hadn't had a chance to find it yet.

Good to know that the laws of physics still apply to ski boats!

Be interesting to see what happens with the new prop .............

 

[QC]

Re: Won't Reach WOT! Please Help!

I use BoatTest.com a lot although I have found mistakes. If anyone has a question about economy etc. I often look there for something similar in size, shape, power etc. The one above is the most efficient Tournament hull I can recall, but it's VERY IMPORTANT to note that the power package is rated at 400 bhp . . .

 

[MikDee]

Re: Won't Reach WOT! Please Help!

If your engine is setup to run 44mph @4400 rpm max at WOT, then you are close to where you should be!

A formula I have memorized from a boating handbook many yrs ago for figuring top speed knowing the rpm, gear ratio, and prop pitch, has always worked almost dead on for me, for yrs: (Prop pitch, minus 1, times prop rpm (after figuring the gear ratio) = speed minus % of slip = approx final speed)

Example: 13" pitch, minus 1 = 12" pitch X 4400rpm (at 1x1 gear ratio) = 52.800 mph, minus 15% slip = 44.880 approx top speed (easy as pie to figure! )

Thus, a 13" pitch, -1 = 12" pitch X 4000rpm = 48.00 mph, minus 15% slip = 40.8mph approx top speed (very close to your GPS reading, I'd say your tach is off!) This is why it's physically impossible to be doing 40mph GPS with a 13" pitch prop while reading 3200rpm!

Just as a working example for back up, I previously mentioned to QC, I had an old 18' Higgins all plywood inboard speedboat yrs ago with a rebuilt 135hp 6 cylinder greymarine, with a direct drive trans. & a 12"x12" prop, that would top out at 4000rpm and approx. 38mph!

As such, a 12" pitch prop, -1 = 11" pitch X 4000rpm = 44.00mph, minus 15% slip = 37.40mph!

I'd say your prop looks a bit ratty to me, probably even worse in person, so this very well could be your main problem.

 

[buggiedad_67]

Re: Won't Reach WOT! Please Help!

you could check the butterflys and make sure they are not opening past center at wot, if they do it will cause a lack of rpm and a make it run rich.

 

[1000dollabill]

Re: Won't Reach WOT! Please Help!

I've got to head out of town for about four weeks. However, during that time I'm going to round up a prop, shop tach, and some sort of gps. I've only put gps in the boat twice (street gps), and used the mph reading off that (which was spot on in the truck) to check my speedos. The face of the speedos has two knobs, one for the target speed needle, and the other one I will assume is for adjusting the reading. However I've never touched it. Someone else may have though. Also, one of my pitots busted off on the trailer, so I'm only getting the one reading.

After doing the above, I should be able to determine whether it's the drive line or my motor. I really want to believe my tach is off. I've got plenty of hats, and I'll surely eat one of them, if that's the case.

If it comes back pointing at the motor, I'll probably take it to a marine mechanic. I'm at my wits end with this boat. It would be worth spending the money to avoid the aggravation this boat has caused me. With all the new parts, I would think they can't hit me with too many more. Anybody know of an honest, reputable marine mechanic in the Atlanta area? The guy I talked to left me high and dry today, so I guess I'll find someone that does want to make some money.

At least one of my numbers in the equation is off. Wouldn't surprise me if both the speedo, tach, and pitch were inaccurate. The prop does look worse in person, blades look wavy, pitted, and ground down. I banged the prop once, and who knows about the previous owner.

I do thank you for your replies and suggestions. Hopefully this season this boat will run right.

Thanks,
Bill

 

[45Auto]

Re: Won't Reach WOT! Please Help!

Good luck, Bill!

Wish I was closer to give you a hand.

Let us know how it turns out.