Am I Underpowered?

[longshanks]

I am running a 50 HP 4-stoke outboard, pushing a 15' aluminum boat. The whole thing probably weighs a total of 1000-1200 lbs. Boat builder recommends 40HP 2-stroke motor for this hull.

My motor was just re-built, with a new power head, pistons, oil pump, etc. under warranty by a local mechanic. Technically, it should be brand new, but it does not seem to be operating to it's full potential, as far as I am concerned. Recommended RPMs are 5500-6000. Try as I might, I cannot get this motor to spin more than 5200RPMS, and I know my tach is accurate. To do this, I have to empty my boat of all passengers, gear, beer, and fuel, so I am running with a minimum load. I've tried 4 props ranging from 9-13 pitch, and my top RPMs come from a quiksilver stainless 3-blade, 11 5/8 by 11 pitch prop.

I have run the #'s here, and I come up with 12-13% slip, at 5200RPMS. This seems about right for a 6 degree V hull of this weight, I think. My top speed is 26mph, with an 11 pitch prop and 1.83 gear ratio.

The factory tests for this motor show the same brand prop in 11" by 12 pitch will produce 5% slip, on a 17' hull, approximately 400lbs lighter than mine. Their test boat goes 36mph at 6000 RPMs.

So. When I went back to the dealer to tell them that I am not getting performance from this motor, they suggested either decreasing prop pitch (which I've tried) or replacing with a more powerful motor (which I can'
t afford).

Does this difference in performance sound acceptable? Or do you think something is wrong with the motor re-build? I am thinking that something is not right with the motor, but I wanted to run it past some more experienced people to get an opinion.

thanks for your time

 

[QC]

Re: Am I Underpowered?

Well thinking about your other thread and this one . . . My first thought is that the test data is not from the same combo so . . . it really doesn't matter, lighter weight is always better, and the bigger hull could be even better by itself. Also, 5% slip is race boat stuff, and very light fast ones at that.

What's your altitude? How did it run before the rebuild? I usually don't supect rebuilds for power issues except break-in stuff and possible mistmatched parts. Other than that, performance is air, fuel and spark . . .

 

[pwiseman]

Re: Am I Underpowered?

I had a Lund Explorer 1650 with the merc 50 EFI. It was 16'8" and probably weighed about 800 lbs. Motor is around 260 if I recall that right. I ran a 13 pitch and got about 34 MPH.

Thinking if you are mouted well, you should get similar numbers perhaps a little less as you are a couple hundred more lbs. 50 HP is enough.

 

[longshanks]

Re: Am I Underpowered?

running at 2200' asl.

prior to the re-build, it seemed to be considerably faster out of the hole, and although I never did run it at WoT, it seemed to be faster to me. BUT, I did not have a tach on the motor, nor a GPS. I was only able to run it once, for a short time, before it overheated, which lead to the re-build. I was told by the mechanic that the sensor on the engine showed either an 'overspeed' or an 'overrev', as well as an overheat. At this point, I am trying to track down if it did actually over-rev. If it did get over 6150RPMs, using the same prop and mounting height, we know that we are around 1000 RPM's lower than that now, which probably indicates a problem with the re-build.

How much should I expect the RPMS to increase once the motor is fully broken in? So far I have about 6 hours on it, using different props, since re-build. I am hesitant to run it much more, unless I am reaching the proper rev window.

And, I'm not that eager to throw more $ at props, if there might be a problem with the motor.

 

[longshanks]

Re: Am I Underpowered?

here is a photo of the boat.

6 degree vee, probably around 1000 lbs empty, maybe less.

builder recommends a 40 2-stroke.

it has a tunnel about 3" deep, 10" wide, and 24" long. Prop does not cavitate, at all, and the AV plate is just above the top of the tunnel.

I can only dream about 34mph at this point, and I am thinking something must be wrong with this re-build?

 

[pwiseman]

Re: Am I Underpowered?

running at 2200' asl.

prior to the re-build, it seemed to be considerably faster out of the hole, and although I never did run it at WoT, it seemed to be faster to me. BUT, I did not have a tach on the motor, nor a GPS. I was only able to run it once, for a short time, before it overheated, which lead to the re-build. I was told by the mechanic that the sensor on the engine showed either an 'overspeed' or an 'overrev', as well as an overheat. At this point, I am trying to track down if it did actually over-rev. If it did get over 6150RPMs, using the same prop and mounting height, we know that we are around 1000 RPM's lower than that now, which probably indicates a problem with the re-build.

How much should I expect the RPMS to increase once the motor is fully broken in? So far I have about 6 hours on it, using different props, since re-build. I am hesitant to run it much more, unless I am reaching the proper rev window.

And, I'm not that eager to throw more $ at props, if there might be a problem with the motor.

What year is that motor? Thinking 04 was first year they had EFI on the 50. Should have a beeper go off on over rev. and it is loud.

Also break in procedure for that motor should be something like this:
hour 1 - do not go over 1/2 throttle and vary speeds up and down

hour 2 - do not go over 3/4 throttle and vary speeds up and down

hour 3-10 - do not run WOT for more than a a few minutes at a time.

You should check your manual on that to double check.

 

[pwiseman]

Re: Am I Underpowered?

I would try one more thing. If the weight of the 4 stroke is a factor, and it sounds like it could be, try placing 150-200 lbs of sand bags (or whatever) in very front of your bow. That might make it sit more like a 40 2 stroke, but you would have 400 extra lbs.

 

[Chris1956]

Re: Am I Underpowered?

'shanks, I do not think your motor is performing properly. That 50HP should easily push that boat to 30MPH+.

You might examine the plugs for proper color and check compression. Compression should be 100+PSI and even on all cylinders.

 

[longshanks]

Re: Am I Underpowered?

thanks for the input guys.

Regarding weight of this motor, I really don't think that it is a significant factor. The 50 HP 4-stroke weighs 250lbs. I have also tried a 60HP 2-stroke motor on the same hull, with a jet pump. It weighs around 260lbs. The jet pump effectively reduces the 60HP to about 40HP, yet it has a good holeshot, and still goes up to about 30mph. I have run the 4-stroke motor with extra weight in the boat, and my rpms drop down to around 4800-5000WoT, and top speed and hole shot suffer significantly.

The mechanic who rebuilt the motor has gone over it completely, and found no problems. 180# compression on all four cylinders, and throttle plates opening 100%. I am wondering if there could be some sort of mysterious problem with the ECM on this motor? At any rate, once it was re-built, I was overall disappointed with the performance of it. I never had a real good opportunity to run it before it was re-built, but it sure doesn't seem like it is making 50HP.

Any ideas on how I deal with this are appreciated...

 

[pwiseman]

Re: Am I Underpowered?

Wondering if you have any potential for water weight to be hiding in foam or floatation. Good way to find out is to weigh the boat motor and trailer, then weight the trailer. If your weight seems to high, this could be the issue.

 

[longshanks]

Re: Am I Underpowered?

Hi again.

Motor is an '06, with around 32 hours on it now. It has been re-built twice, under warranty. First at 0 hours, second at 26 hours (just after I bought it). Since then, I followed break-in procedure.

I don't believe water soaked foam is an issue. I had it all apart last year, and it is stored indoors, on a trailer, with drain plugs removed. I have not weighed my boat, but when the motor was in for re-build, I ran this hull with my 40 jet, and the difference in performance is clear.

Before it was re-built, the motor was squawking away with continuous tones, that I took as 'overheat'. If it over-revved, I didn't notice any different tones. I am told it could have been 'over-speed', with is apparently different than 'over-rev'?

Anyway, warranty on this motor runs out June '08, and I want to get this resolved. Despite what my mechanic says, I don't think this motor is performing, and I need to figure out what I have to do, to get Mercury's attention.

 

[pwiseman]

Re: Am I Underpowered?

Hi again.

Motor is an '06, with around 32 hours on it now. It has been re-built twice, under warranty. First at 0 hours, second at 26 hours (just after I bought it). Since then, I followed break-in procedure.

I don't believe water soaked foam is an issue. I had it all apart last year, and it is stored indoors, on a trailer, with drain plugs removed. I have not weighed my boat, but when the motor was in for re-build, I ran this hull with my 40 jet, and the difference in performance is clear.

Before it was re-built, the motor was squawking away with continuous tones, that I took as 'overheat'. If it over-revved, I didn't notice any different tones. I am told it could have been 'over-speed', with is apparently different than 'over-rev'?

Anyway, warranty on this motor runs out June '08, and I want to get this resolved. Despite what my mechanic says, I don't think this motor is performing, and I need to figure out what I have to do, to get Mercury's attention.

There are differernt beeps for different warnings. I believe these are in the manual. I very occasionally got air and thus cavitation, and it was a long single beep. Never caused any problems for me.

Did you every notice your telltale stream not comming out? Some people call it peehole or peestream.

These motors are pretty smart about shutting down when there is a problem.

Hard to understand what is causing overheat, but I am wondering about your how you are mounted. If you are not getting a clean stream of water to the prop, this might explain a lot of things.

 

[longshanks]

Re: Am I Underpowered?

well, the overheat problem was a motor problem, it had nothing to do with my setup. It was resolved, when the motor was re-built. There were problems with water pumping, but again, not since it was re-built. As far as I can tell, there never have been any problems with cavitation, or ventilation, ever. Since the re-build, the motor has run smoothly, with no faults or alarms, but only up to a speed of about 26mph, @5200 RPMS. From what I understand about 4 strokes, unless the motor is turning near the top of the RPM window, performance suffers. This is what I am experiencing. The motor works fine, but I am getting no performance out of it, and I can't figure out why. I've tried different props, but none of them have come within less than 800RPMs of the 6000 I'd like to get out of it. I've left the problem with Mercury, but I haven't heard anything definitive back from them as of yet.

 

[Chris1956]

Re: Am I Underpowered?

'Shanks, 4 cycle engines have good power at low and mid RPMs. It is the 2 cycle motors that you want to rev up to get the power.

Why was that motor rebuilt at zero hours? Why was it rebuilt at 23 hours? quite strange, I think.

With 180 PSI, that motor should make its full power, that is if all cylinders are working properly, the timing and fuel systems are good etc.

 

[longshanks]

Re: Am I Underpowered?

Chris, I've been told that this motor will perform poorly, unless it is operating at or near the top of its RPM range; 6000. Other four strokes I've operated that spin near the top of their range perform as well as I'd expect, and have a lot more 'zip' than mine, which is running below the RPM window.

I bought my motor with 24 hours on it. It overheated when I ran it. As I found out, it was seized at 0 hours, by the original owner, a fishing resort. Might have been run without oil? When they re-built it, they neglected to clean approximately one cup of piston chunks out of the motor. I agree with you that this is 'strange'! These chunks appear to have subsequently restricted oil flow to the pistons, and caused the motor to overheat a few times. Mercury came good on the warranty, and has replaced the powerhead for me, the second owner, at 25 hours. However, the motor doesn't have the same power that it did when I ran it before it was re-built.

I've owned the motor for 10 months now, and it hasn't worked properly yet. If I could sell it, I would, but I'm not going to sell a motor that doesn't work properly. If I can get it to perform at 50HP, I'll gladly keep it, as it's more or less a brand new motor.

 

[Chris1956]

Re: Am I Underpowered?

'Shanks, So it has a new powerhead. That narrows the lack or power down to fuel or ignition. It should run perfectly, unless the mechanic really messed it up.

Time for another mechanic?

 

[longshanks]

Re: Am I Underpowered?

Update on this -- I have an appointment to put the motor on a dyno, at a local shop. We're going to find out how many HP the motor is producing. I will provide another update in a few weeks, when we get some answers.

 

[pwiseman]

Re: Am I Underpowered?

Update on this -- I have an appointment to put the motor on a dyno, at a local shop. We're going to find out how many HP the motor is producing. I will provide another update in a few weeks, when we get some answers.

Sounds like a good direction. Sure seems all the info you posted would indicate you should get better perfomance

 

[v1_0]

Re: Am I Underpowered?

No expertise on this, but it sounds like you are being protected...

ENGINE GUARDIAN uses more than 40 sensors to monitor functions of your engine. If the proactive operator-warning system detects a potential problem - such as overreving, overheating or low oil pressure - Engine Guardian sends out an alert and automatically reduces engine power to prevent damage. [Mercury Web Site]

Maybe one of the 40 sensors is defective or 'pointed the wrong way' (figuratively speaking). Or the power reduction system is 'on' when it should be off...

On a related note: obviously this didn't work too well for the previous owner.

-V

 

[MikDee]

Re: Am I Underpowered?

If your throttles are opening completely, and you have that much compression, I would go over anything petaining to fuel delivery, from the antisiphon valve, & tank pickup, to the carbs, and see to it your timing is advancing fully.