Won't Reach WOT! Please Help!

[1000dollabill]

89 Ski Centurion Falcon
Indmar 351W
Borg Warner 1:1 Trans
13X12 Nibral Prop

Engine Won't Reach Operating RPM. Check

* Fuel condition. Type and Octane possibly old fuel Many fresh tanks of 93 octane
* Propeller pitch or diameter, damaged blades Cavitation burns and pitting on blade surfaces
* Restricted fuel pickup tube or anti siphon valve Fuel System Test tested fine and visual inspection
* Crankcase oil volume, high oil level can cause aerated oil and lifter collapse On the mark on the dipstick
* Marine growth on hull and outdrive Boat lives in the garage, bottom clean
* Wrong gear ratio in outdrive noted above
* Restricted carburetor air intake (clogged flame arrestor) cleaned and inspected
* Restricted exhaust system (broken exhaust shutters/flappers) in engine transom shield or drive removed manifolds and risers, inspected entire exhaust system
* Poor cylinder compression Compression Test all cylinders tested at 125 psi
* Carburetor defective, or wrong type. Brand new holley 4160
* Fuel pump pressure and vacuum brand new fuel pump, lines, seperator, tested good
* Boat overloaded, improperly loaded, or improperly trimmed. no trim, no passengers
* Engine Overheating never runs hotter than 160
* Engine timing and ignition system operation new coil, resistor, cap, rotor, wires, plugs, distributor, timing correctly set
* Remote control cables and linkage for proper travel to open throttle plates fully. yes


I don't remember the results of the tests and timing because it was last season. However they were good per the spec sheet.

Boat runs 40mph at 3200RPMS. Will not exceed 3200. It's supposed to run 44mph at 4400rpms.

Could this be all attributed to the prop? I'm going to order a new prop this week. Any other ideas?

 

[a70eliminator]

Re: Won't Reach WOT! Please Help!

Try useing another tach, if the rpm's are equal then maybe another prop?

 

[MikDee]

Re: Won't Reach WOT! Please Help!

Prop seems like the right numbers, unless it's damaged? What is the ignition point gap? Dwell angle? By the way, everytime you set this, you must reset the ignition timing (that's a given). Also, do you have the correct spark plugs? and how do the old ones read? 125lbs compression is a bit low, but if tuned right that 351 should still crank more then 3200rpm.

 

[bruceb58]

Re: Won't Reach WOT! Please Help!

Check the timing again but look at the max advance at high RPMs...you will need an advance type timing light to do this. If your distributor is not giving full advance, it will limit your top end.

 

[1000dollabill]

Re: Won't Reach WOT! Please Help!

Sorry my numbers were off. My post from last season was 135psi per cylinder. As far as dwell and ignition settings I know the gap is 18, base timing if I recall is 10 degrees BTDC, it acted the same with electronic ignition installed. The distributor is brand spanking new. Have gone through 5 sets of the correct plugs. The prop edges look a little ate up, and also the cavitation burns and pitting. I would think the prop would be slipping, not bogging. Keep the ideas coming.

Thanks,
Bill

 

[bruceb58]

Re: Won't Reach WOT! Please Help!

What I was asking in my previous post was not what the base timing was but if it advances properly with RPM.

 

[MikDee]

Re: Won't Reach WOT! Please Help!

Good point Bruce, the distributor advance mechanism (weight's, & springs, usually under the breaker points plate) maybe rusted, & binding up, and not delivering full advance at WOT. (usually around 30degrees total at the crank)

By the way, I don't understand how you get cavitation, or ventilation burns on a prop that's never run out of the water?
Besides, I doubt the prop would be slipping, unless it was in seaweed, or you'd actually see more rpm on your tach, with your boat not going any faster.

 

[ziggy]

Re: Won't Reach WOT! Please Help!

By the way, I don't understand how you get cavitation, or ventilation burns on a prop that's never run out of the water?

ventilation is just sucking air. which don't push yer boat fwd and allows yer engine to rev. wildly. it don't hurt yer prop.
cavitation occurs when the blade of a prop cuts thru the water. it creates a low pressure on one side of the prop blade. if the pressure becomes low enough, water atoms seperate and turn into steam (gas). as the steam bubbles reform into water at the outer edge of the prop. when they do, it's like hitting the prop with a hammer and the water drops hit so hard, they literally take chucks of metal off the prop blade.... that's the way i get it anyways. google cavitation if ya really want the low down on it.... i think after ya confirm yer advaceing proper. i'd be lookin at that little ate up prop as ya discribe it... which it sounds like yer doing....
so why the carb replacement? was it reachin wot with the old one? is that the direct replacement carb or oem one?

 

[1000dollabill]

Re: Won't Reach WOT! Please Help!

I checked the advance last season and it does fully advance ~30 degrees. The distributor and it's guts are brand new. Last season it was backfiring through the carb and the exhaust and wouldn't bust the 2800 mark . That turned out to be a weak fuel pump and the wrong carb (automotive.) Since I take the nephews out on the boat, I wanted everything to be "marine" USCG approved. Now she runs fantastic. However at 3200RPM's if I push the throttle to wide open, you can here a loud humming (don't think it's the secondaries), and nada (loading up.) Will eventually backfire out the exhaust from unburnt fuel. I do think the boat's dragging *** a little bit. The wake plate is cranked all the way down. I read that cavitation can create a "hole" that the rear of the boat falls in, but not sure how that might affect an inboard.

 

[a70eliminator]

Re: Won't Reach WOT! Please Help!

in your first post it appears you've got everything pretty well covered, there is one other scenerio I can think of and that would be your boat is carrying several hundred pounds of excess weight due to saturation of floatation foam under the deck and that windsor is pulling all she can.

 

[ziggy]

Re: Won't Reach WOT! Please Help!

The wake plate is cranked all the way down.

does that mean yer in the mode to create drag and make a bigger wake?

 

[Maclin]

Re: Won't Reach WOT! Please Help!

If the 40mph is correct and the 3,200rpm reading is correct......

40 at 3,200rpm versus 44 at 4,400rpm is one heck of a change in prop or gear ratio. Theoretically if you COULD get the engine to somehow pull past the 3,200 rpm mark and go to 4,400ropm you would be going 55mph plus or minus prop slippage. See what I mean? Your gear and prop combo is way off if the 44mph @ 4,400rpm is the goal. So with the extra drag from the wake gate that is all she has brother.

In my opinion you need to change one or the other or both (gear and prop).

 

[QC]

Re: Won't Reach WOT! Please Help!

Whoa!!! The tach is off . . . period!!!! a70 mentioned this in the first reply and then a train wreck developed. Maclin came close and then got into ratios etc.

If it is truly a 12" pitch with a 1:1 ratio 40 MPH @ 3200 RPM is negative 10% slip. No way, no how. That means it is going 10% faster than the 12" would go with 0% slip . . . Impossible with any prop, engine, boat, period. Inboards do well to get 15% slip. I think she is running closer to 4200 RPM as is . . . All of that other stuff could still be an issue, however, unless the tach is correct this is a stupid exercise. Do NOT change the prop yet. Need to get solid data before you make any changes.

P.S. to MikDee . . . You do NOT have to get a prop into the air to get Ventilation or Cavitation. Both can happen with a 10 ton inboard cruiser . . . Ziggy has this right.

 

[1000dollabill]

Re: Won't Reach WOT! Please Help!

I had thought about that (tach), however it will rev to the moon ~5000 rpms in neutral (I don't make a habit of free revving.) Not to mention it is not actually running WOT at 3200 rpms (more like 3/4 throttle). If I push it to WOT it will just cause a resonating sound (like blowing over a coke bottle). Loud enough I can't here myself think.

I bought the boat and it would only rev to 2800 backfiring, missing, and generally a POS. It would not surprise me in the least if the prop was at sometime repaired by a halfwit, hammer, and 2X4. I will check the tach but I'm fairly certain it's not that far off.

The wake plate is actually like a trim tab. So angled all the way down, I would think it would bring the bow down. However, angled all the way down it is nearly level with the bottom of the boat. I can't find much literature on a "wake plate," so if anybody knows that would help too.

Is it possible the prop's pitch was changed from hitting a sandbar or something, better yet, could it change that drastically?

 

[QC]

Re: Won't Reach WOT! Please Help!

Quick blip on the throttle is not indicative of anything as the needle could bounce up. The only way that boat goes 40 MPH @ 3200 RPM with a 1:1 gear is with a 16" pitch . . . possible, but 40 MPH is not that far off. Oh, I don't recall seeing this, is that speed GPS? Anything else we are also potentially chasing ghosts.

Yes, your pitch could change from whacking a sandbar, but again 40 MPH is not that far off, and I would be very surprised if a sandbar modified prop would be an efficient 16" pitch. Oh and if it is supposed to run 44 at 4400 that's 12% slip. I figure 15% is more average and that would say 42.5 MPH at 4200 . . . I can't comment on the increased noise with the last bit of throttle, but I have seen that before. My guess is the engine and hull have kinda hit their max and a little more throttle doesn't get you anything, but without good info, playing with the carb, timing etc. is ludicrous. Personally I think the tach is off by 1000 RPM at WOT

 

[45Auto]

Re: Won't Reach WOT! Please Help!

As QC says, your numbers don't make sense. Your prop is turning slower than the speed you say the boat is moving. Kind of like saying "the wheels on my car aren't turning but the car is moving at 40 MPH".

Either the RPM, MPH, prop pitch, or transmission ratio is wrong.

I figure your RPM came from the factory tach, hopefully it's fairly accurate.

Is the speed from a GPS? Factory speedos can be pretty far off.

Is the prop pitch stamped on the prop or did someone tell you those were the specs?

I'm not too familiar with direct drives, is the ratio stamped on the transmission or from a data plate maybe?

Hard to make a logical diagnosis of your problem when it isn't physically possible!!!

 

[QC]

Re: Won't Reach WOT! Please Help!

It's probably just the Cyl switch on the back of the tach. But perfectly set up 351s in a Tournament type hull rarely break 45 MPH, so this just isn't far enough off for 3200 RPM no matter what's underneath . . .

Funny, but I never trust tachs unless verified, however, on a Tournament boat the Speedos should be VERY close . . . I say Speedo(s) cause they usually have two for verification. On the tach thing, they are usually very accurate when they are setup right as they are simply reading blips from some source, if that source blips too often or not enough and the correct conversion is not in the tach head, then who knows what it will read . . .

 

[45Auto]

Re: Won't Reach WOT! Please Help!

My first thought also was a tach switch in the wrong position, but I think that would make it read too high instead of too low. Only one way to go wrong (on the too few cylinder side) since it's a V8. Tach could just be bad though. Good point on the speedos.

Something's wrong somewhere, more than a tach being off. No way it should be backfiring after running at WOT for a few minutes.

However at 3200RPM's if I push the throttle to wide open, you can here a loud humming (don't think it's the secondaries), and nada (loading up.) Will eventually backfire out the exhaust from unburnt fuel.

My bet is something is hosed up in all the new ignition parts and the new carb installation. Don't know your background 1000dolla, but the best thing to do would probably be to get with someone experienced and start at the beginning and work all the way through it. If your profile had your general location, somebody might be close enough to take a look at it with you.

 

[QC]

Re: Won't Reach WOT! Please Help!

Good point on the tach. Which way does it go if it is set for a two-stroke OB? Would read low I think? Maybe it's setup for an Indmar V10 . . .

 

[whywhyzed]

Re: Won't Reach WOT! Please Help!

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